This thread is about the French tanks designed or contemplated for the new tank program drawn up by the French Inspector of Tanks in December 1939-February 1940, Général Keller.
This wartime program was intended to organize development of tanks in control of the infantry branch (infantry support, battle, and fortress tanks) that could take part in the battles of 1941-1942, and emphasized the following points:
- general increase in the weight of infantry and battle tanks, which means a decrease in production either due to their complexity requiring new and rarer tooling or simply due to lack of steel (the impact of armor steel supplies from the British is to be considered)
- general increase in firepower, mobility and protection
- the need for rapid development requiring a move away from peacetime procedures. All tank-related private and state-owned design bureaus must be involved on the minimum amount of studies. In some cases, tanks with proven ideas and parts can be ordered straight from the mockup stage without a normal prototype. There is obviously an emphasis on using proven components and standardizing parts where possible.
The committee in charge of reviewing the program distinguished two categories:
- interim/transitional/stopgap tanks which can enter production in the Spring of 1941 at the latest
- future tanks which can enter production in Spring 1942 at the latest
Present knowledge indicates that the following designs were considered as part of this program:
Char d'accompagnement de l'infanterie/Infantry support tank:
- interim: AMX 38
- future: an offshoot of the Char de 16 tonnes Renault aka Renault DAC 1
Char de bataille/Battle tank:
- interim: B1 Ter, Renault G1R
- future: B40 (studied by the ARL), AMX Tracteur B
Char de forteresse/Fortress tank:
- interim: FCM F1
- future: none known
Posts/edits about the requirements of the program and the related tanks to follow.
The following is a translation of the required characteristics for the future infantry support tank.
Requirements for the future infantry support tank:
I - General characteristics
Crew: 2 men
Armament: 1 47mm SA 35 gun and 1 7.5mm machinegun in the turret. Aiming of the armament only through turret traverse is allowed as long as it is as fast and easy as with current turrets (referring to current turrets having independent horizontal traverse for the gun). This saves weight and space.
For the machinegun: independent horizontal traverse for firing on the move.
Powered and 2-speed manual traverse.
Ammunition capacity: 80 rounds of 47mm. 3000 rounds of 7.5mm (in 150-round mags).
Armor: Equivalent to 60mm on parts outside of:
- the front floor which will be 30mm thick
- the rear floor and the roof which will be at least 20mm thick
Engine: 10 metric hp (PS)/t
Maximum speed: 25 kph on road at the minimum. Minimum speed: 2 kph at maximum torque.
Offroad speed: 13 kph at least on flat dry plowed ground.
Range: 8 hours
Trench crossing capability: 2 m Wading height: 1m Ground clearance: 40cm Wall climbing capability: 0.80m Maximum slope: 100% Usual inclines: +-45° longitudinally and +-35° transversely.
Maximum weight: 20 tonnes fully loaded, not to be exceeded
Ground pressure: average 0.8 kg/cm2 on soft ground when ribs are dug in. Maximum pressure under the most loaded track link: 1.5 kg/cm2 on wet ground when ribs are dug in.
II - Particular characteristics
Means of access: This must include 2 doors (one in the turret) and an escape hatch that can be easily opened from the exterior of the tank. The hull, the assembly of miscellaneous elements, and the disposition of internal organs must allow accessibility to essential elements and easy removal of assemblies.
Engine: This must use diesel or gasoline. In the latter case the gasoline must be of the standard military type (65 octane).
Electrical equipment: This must be shielded against interference to improve radio operation. The capacity of the accumulator battery and the flow rate of the charging dynamo must allow normal use of the radio.
Suspension - Transmission - Steering - Braking
The suspension must be done with separate elements. The sprocket will be placed at the rear to maximize space inside the fighting compartment. The transmission, if equipped with a differential, must include a blocking system for it.
Maximum steering effort by the driver must not exceed 20 kg. If the number of speeds is limited, there must not be a large gap between speeds.
Starting of the engine must be ensured with a double electrical and mechanical starting system that can be used from inside the tank.
The braking system must allow immobilization of the vehicle on the maximum slope the tank can climb.
Tracks with sufficiently high pitch.
Roadwheels: many.
No protection for the upper run of the track.
Soft suspension.
Vision devices: PPL episcopes and Gundlach-type periscope
Ventilation and protection against gases: semi-collective protection system analogous to the system being studied for the B1 Bis. Separate ventilation systems for the fighting compartment and engine bay. Depression inside the fighting compartment.
Protection against fires: done with a fireproof bulkhead. The resistance of the bulkhead attachments and doors must be sufficient to withstand an average pressure of at least 3 kg/cm2.
Misc: gasoline fuel tanks must be equipped with filling limitators and must be self-sealing.
The piping must be rigid or flexible depending on whether the organs linked with this piping contribute or not to the same vibrating motion.
Light weight must be sought for the miscellaneous elements (accessory holders...) fixed to the walls of the hull.
It will be useful to include a fake floor on which the attachments and holders needed for the fixation of organs will be fixed to protect against anti-tank mines.
The entire spec must be met regarding protection and armament, while staying within the weight limit to not excessively reduce transport possibilities. It will be possible to accept a reduced range if we can improve refueling means (high flow rate pumps, specially designed fuel tanks). Lower speed can also be accepted.
Overall, the future infantry tank spec retained the same principle of restricting weight and cost through the use of a 2-man crew to assist the infantry.
It emphasized a reinforced armament and armor to deal with anticipated enemy tanks and antitank guns, as trials on the previous light tanks with a 40mm-basis showed they could be penetrated by French 25mm AT guns in certain conditions. The French also referred to British Matilda I and II infantry tanks to indicate the trend towards 60mm or more.
It is worth noting that the French definition of armor basis since 1937 is that the armor must be equivalent to the basis thickness EVEN if the tank is angled at +-30° for the frontal arc and +-20° for the sides, due to the natural movement of the tank on uneven ground. So they had to assume the worst case scenario, which means that for example armor sloped at 30° from the vertical must still be 60mm thick. This results in angled parts of the armor being significantly stronger than the basis thickness when on flat ground.
The spec also incorporated lessons from the limited Saar offensive of 1939 and general use of previous light tanks in peacetime and during that offensive. This is why the protection against Tellerminen antitank mines was reinforced, and the tank was prepared for good use of the radio (electrical shielding and battery capacity). Crossing capability is also improved, as the lighter previous tanks had difficulty crossing certain obstacles. Mobility is brought to the typical French minimum of the mid 30s, 10 hp/t and 8 hours of range, which could not be obtained on previous light tanks due to weight creep during development.
This also includes recent developments like protection against gases, powered traverse (IIRC the APX-R was manual), and deletion of the independent traverse arc for the gun. The machinegun is considered suitable for firing on the move.
More must be said on the suspension and protection of the upper run of the track. Experience with the Renault R35 light tank demonstrated severe mobility/ground pressure issues on wet ground. The French identified the short pitch of the track, the large spacing of the roadwheels and their heavy loading as the cause of the problem. Hence, they generally emphasized using the same principles as the Char B1: large pitch and many small roadwheels.
The protection of the upper run of the track was done on the FCM 36 and the B1 Ter. Though mud buildup was not always an issue with well-designed track tunnels, it was decided on this and the Char G1 program to not make this feature mandatory to save on weight. Skirts for the suspension elements themselves was still allowed.
Renault, Hotchkiss, FCM, Panhard and SOMUA had also been contacted. So for all we know, we may have seen projects from these companies if France hadn't fallen.
I - General characteristics
Armament: 1 47mm mle. 37 (MV 855 m/s) gun and 1 7.5mm MG in a turret.
A hull gun of 75, 105 or 135mm caliber firing a projectile with a large explosive charge and highest possible muzzle velocity to attack antitank obstacles.
--> later updated to a 75mm SA35 or if possible a 105mm gun with reduced muzzle velocity, automatic breech and cased ammunition.
Minimum range 50m, maximum 2000m. 1-2 7.5mm hull machineguns.
Horizontal traverse of the turret gun will be achieved solely with the turret itself.
Aiming of the coaxial MG will be independent from the gun thanks to a separate mask.
Rough aiming of the hull gun with the tracks, to be finished with manual traverse of 2-3° either side of the axis.
The turret will be crewed by 2 men.
-10/+18° vertical traverse
Spent cases recovered in waterproof bags. Crew: 1 commander/47mm gunner
1 47mm loader/7.5mm coax gunner
1 driver/hull gunner/hull MG gunner
1 radioman
1 hull gun loader
In the case where voice radio (ER 28) was possible for communication between tanks, the radioman could be the commander. The crew could then be reduced to 4 unless the hull gun requires an additional man (operation of the scavenging system).
Ammunition: 50 47mm rounds, 50/50 HE/AP mix.
60 rounds for the hull gun.
2000 7.5mm rounds per MG
Armor: Equivalent to 80mm for parts other than
- the forward part of the floor: 40mm
- the rear part of the floor and the roof: 30mm
No direct fixation on the forward floor.
Range: 8 hours, unless quick refueling can be possible every 4 hours. Power: 12-15 hp/t (initially 8-10) Maximum speed: 40 kph Speed on plowed dry ground: 15 kph Crossing capability: 3 m Ground clearance: 50 cm Weight: 40-45 t Ground pressure: 800 g/cm2 on average, not exceeding 2 kg/cm2 with ribs dug in.
Communication device: throat microphone Means of liaison between tanks:
- telegraphy: 5km range
- voice: 2km range
Vision devices: episcopes if possible, Gundlach periscopes and sight.
II - Particular characteristics
Engine:
- double starting system
- electrical shielding for gasoline engines
- use of the 65 octane army gasoline
- works in usual conditions for offroad vehicles on high slopes (up to 80° for short moments)
Fuel supply:
- filling limiters on the gasoline fuel tanks
- piping will be rigid inside the same assembly
Cooling:
- sufficient for an ambient temperature of 30° C
Transmission:
- blocking system for the differential
Brakes:
- able to stop the tank on the steepest ramp it can climb
Steering:
- maximum steering effort should not exceed 20 kg for the driver
Tracks:
- traction resistance of 150 t for each track
- rear sprocket
- set up so that a mine explosion at the front doesn't destroy the entire track
Suspension:
- not very vulnerable
Radio: the capacity of the battery and the flow rate of the dynamo must be designed with the radio system in mind.
Semi collective protection against gases.
Fire:
- remotely operated fire extinguishers
- Fireproof bulkhead able to withstand a pressure of 3 kg/cm2
Access means:
- 2 doors and 1 escape hatch that can be opened from the outside
The hull, the assembly of miscellaneous elements, and the disposition of internal organs must allow accessibility to essential elements and easy removal of assemblies.
Misc:
Fording 1.5m
Wall 1m
Ramp: 85% of the Vincennes track
Assembly of the hull: the elements of the carcass must be assembled with wedging recesses, welding or large bolts. Full use of welding is emphasized.
It will be useful to include a fake floor on which the attachments and holders needed for the fixation of organs will be fixed to protect against anti-tank mines.
Overall, the new spec called for a similar general concept to the B1 (Ter), but with even thicker armor, and more importantly with a heavy emphasis on greater mobility (speed, range, power/weight ratio) and antitank armament (2-man long 47mm turret). It was also desired to increase the caliber and thus payload of the hull gun to deal with antitank obstacles.
This spec posed particular problems, as the committee in charge of future tank development very much feared that the weight would actually baloon to 55-60 tonnes. Previous research had shown that the limit for road travel was 35 tonnes, which was later increased to 45 tonnes without reinforcing bridges.
The committee decided that any project exceeding 40 tonnes would be rejected, to allow a growth margin during development. Since there was a concern the tank would not meet all requirements at this weight, it was decided to accept the following concessions in that order:
1°) Power: at least 10 hp/t
2°) Armor: minimum 70mm
3°) Minimum 8-hour range
4°) Long 47mm gun in turret and 75 SA 35 in the hull
So the increased antitank power had the highest priority.
Engineer LAVIROTTE of the Rueil arsenal (ARL) had estimated that a B1 Ter modified to the spec (80mm of armor and 47mm gun and required upscaling) would reach 42 tonnes.
Keller emphasized the need for a powerful armament including an AP gun and a gun with large explosive payload to attack targets with high efficiency and allow the tank to make its way through the passive and active obstacles of the battlefield. It was also needed to give it a very high tactical and strategic mobility as it was designed to be the main element of the DCR divisions. As such, speed (high P/W ratio) and weight had to be carefully studied. A reduction in range could be envisionned.
Outside of the state arsenals, the following design bureaus were to be contacted: Renault and FCM.
Last but not least, the future fortress tank, before going to the actual designs:
Requirements for the future fortress tank:
Armor:
120mm at the front
100mm at the sides
Armament:
90mm mle. 39 Schneider gun in a turret (or high velocity 75mm as suggested by Keller initially)
135 or 155mm howitzer in the hull
Multiple machineguns (3-4 to cover all sectors)
Vision devices: stroboscope
Command post: independent from the service of all weapons (eg the commander only commands)
The history for that one is simple: the characteristics were close to the existing FCM F1 tank and the 135/155mm gun didn't exist yet, so no new study for that class was contemplated at the moment.
The only difference was the replacement of the 47mm turret on the FCM with a short 155mm gun which can not be used against tanks and has insufficient HE payload (10.2kg max) against concrete. It was deemed desirable, to truly reach the goal sought for a fortress tank, to arm it with a device able to throw a 100-150kg HE charge to destroy fortifications with blast and not penetration effect. But it did not exist yet, studies just started.
"The fortress tank had to be very tough against field guns and the most powerful antitank weapons used in heavily fortified regions (the 120mm spec had been designed with the 47mm SA 37 and the 75mm mle.1897 at 640 m/s in mind). It must not simply be able to attack the openings of the bunkers like the previous spec. Our knowledge of defensive german organisations requires that the tank be equipped with a gun with a large HE payload to destroy or flatten certain obstacles. These considerations led us to envision as primary armament, on one hand a high velocity gun, the 90mm, in a turret, and on the other side, a 135-155mm high caliber gun. The armor thickness will likely prevent the use of PPL episcopes, so we may have to return to the FCM 2C-style stroboscope."
The Keller plan was for the infantry branch's tanks only, so a new cavalry tank would have had to be part of a program of the cavalry branch. So far no one knows if there was any prior to the battle of France.
The wartime orders for Somua S35 and S40 AMCs (combat armored cars) were such that production would at least continue until spring/summer 1941.
However, the Cavalry had been working since 1938 on the program for a "Powerful armored car" to replace both the AMD and AMR classes, initially with a 40mm basis spec but in the end a 60mm spec. Meanwhile the infantry had progressed to 60mm minimum on any class of tank, and AMX was working on the 60-mm-armored AMX-40 which could be seen either as an out-of-spec tracked entry for the powerful armored car program, or an unsollicited proposal for a Somua S35/40 replacement.
So it is likely that the Somua and its 40mm basis would be seen as problematic in the future, at least on the grounds of insufficient armor (if not armament). However implementing 60mm on a Somua while retaining the mobility would require such major automotive changes at the bare minimum that it would count as a new tank altogether. If Somua looked into the future infantry support tank spec which was sent to it, it could probably even serve as the basis for follow-on-S40 work.
So it is likely that a new program would have had to be made at some point. Maybe there was one but just so late we haven't found a doc on it yet, or the archives were lost, or it would have been done at a later date in 1940 and it just didn't have time to happen.
The Keller plan was for the infantry branch's tanks only, so a new cavalry tank would have had to be part of a program of the cavalry branch. So far no one knows if there was any prior to the battle of France.
The wartime orders for Somua S35 and S40 AMCs (combat armored cars) were such that production would at least continue until spring/summer 1941.
However, the Cavalry had been working since 1938 on the program for a "Powerful armored car" to replace both the AMD and AMR classes, initially with a 40mm basis spec but in the end a 60mm spec. Meanwhile the infantry had progressed to 60mm minimum on any class of tank, and AMX was working on the 60-mm-armored AMX-40 which could be seen either as an out-of-spec tracked entry for the powerful armored car program, or an unsolicited proposal for a Somua S35/40 replacement.
supposedly had 60mm hull frontal armor, and the Cavalry placed an order for 600 units on May 1, 1940. Presumably it was a key element of the Cavalry's 1938 program...?
Subsequent to WWII, of course, Panhard based the EBR design on that of the 201, suitably scaled up to mount a much larger gun.
Is there any historical information that the EBR concept, i.e. a more heavily armed 201 variant, was conceived during WWII?
supposedly had 60mm hull frontal armor, and the Cavalry placed an order for 600 units on May 1, 1940. Presumably it was a key element of the Cavalry's 1938 program...?
Subsequent to WWII, of course, Panhard based the EBR design on that of the 201, suitably scaled up to mount a much larger gun.
Is there any historical information that the EBR concept, i.e. a more heavily armed 201 variant, was conceived during WWII?
I think I recall that the May 1940 order for 600 units was to be per the prototype 201, i.e. armed with a turret mount version of the 25mm AT gun...but with an autoloader.
So I would assume that the 47mm armed version would have been the next generation, and (presumably) the next order.
I don't know of an historical autoloader for any of the French 47mm guns. Was an autoloader to be developed, or was the crew count and turret size to be expanded sufficiently to provide a human loader?
Time to finally adress the first actual tank in the program, the interim infantry support tank AMX 38/39.
History:
As with many other AMX products and interim entries into the Keller program, the AMX 1938 actually long predates the program itself. Russian historian Yuri Pasholok dated the start of development to July 1937, but at least we know it was a thing in 1938.
AMX, which was a nationalized branch of Renault created in the second half of 1936, had been involved in the production and improvement of the Renault R35 light tank since then. Improving the R35 followed two (kinda three) separate paths:
- improving existing tanks (which would be hard to structurally modify)
- improving new production R35s, which led to the R40 (see Annex 1)
- studying a radically new tank to correct all core flaws of the design.
It wasn't long before AMX focused heavily on this 3rd path. Rather than retaining the fundamental features of the R35, AMX instead drew heavy inspiration from the then most successful entry in the 1933-35 infantry support tank program: the FCM 36. The 1st Direction (that of the Infantry Branch) praised the FCM for great mobility on rough ground, the use of a rear transmission which reduced clutter inside the fighting compartment and maximized comfort/space, a diesel engine which massively increased range (among other benefits, see annex 2) and welded rolled steel which proved somewhat more resistant than the castings of the Renault R35 and Hotchkiss H35. However, in spite of their best efforts, the FCM was never ordered in large quantities beyond the initial batch of 100 due to its very high cost (which could have been improved on but the Army simply had no time and ressources to focus on this).
Up to and including the first prototype, which was trialled in 1939/40, the AMX 1938 presented itself as a convergent evolution towards the FCM 36, albeit more representative of the improved form of the latter which had been studied in the years leading to WW2.
The engine, transmission and drive sprocket had all been moved to the rear. The engine was initially a LC 4 4-cylinder inline opposed-piston engine offered by the CLM (Engine Company of Lille - Compagnie Lilloise de Moteurs), delivering 100hp much like the FCM 36's Berliet Ricardo could (in a prototype which used the improved series production cooling system which could handle the extra heat. However the actual tanks remained at 90hp for some reason).
The running gear was heavily inspired from the B1, the D1 and the D2 to spread the weight of the tank as widely as possible and improve mobility on wet ground: it used high pitch tracks, and a large amount of small wheels set up in 4-wheel bogies divided in two 2-wheel bogies, linked up by a balancing arm. This was not as conducive to high speed as short pitch tracks with larger wheels, however, due to small wheels wearing faster and having a harder time going over rocks, and rolling resistance being higher. The tank was even longer than the FCM 36, which had the benefit of giving it great trench crossing capability by French light infantry tank standards. The suspension elemnts were protected by a thin skirt, but much like the revized FCM 36 proposals, the upper run of the track was not housed in a tunnel, which reduced risk of mud accumulating in that area and clogging the suspension.
The design then used a Cleveland (Cletrac) controlled differential steering system, which was considered rather conservative by the French. The radiators and cooling fan were on the right side of the engine.
The hull and turret platform were, if anything, simpler than the FCM, with fewer plates and fewer welds needed. The front was particularly efficiently designed, with the entire front plate (from the driver to the forward floor) being made out of a single bent rolled plate, minimizing the number of welds and maximizing structural integrity. A side-effect of this feature was that the very heavily sloped part of the plate (60° from the vertical) was still the same thickness as the rest, which resulted in it being ridiculously stronger than the rest of the front.
The crew was still 2, with a driver and a commander inside the turret. Prior to the construction of the prototype, the APX-R of the R35 and H35 as well as the FCM 36's turret had been contemplated (per the plans), however, it seems that the problems of the FCM 36's turret regarding weld cracks when using the more powerful 37mm SA 38 gun led the AMX to design their own turret. This was used on the 1st prototype, and was a very simple prismatic design using welded rolled plates, an internal mantlet, and unlike the FCM, only a Gundlach-type periscope for panoramic observation instead of of a turret extension with episcopes (but there was one episcopes/vision slit on either side). The access door was at the rear, as usual for French turrets.
The expected weight of the vehicle of 13.5 tonnes, as well as the desire of the Infantry to have about 10 PS/t on infantry support tanks, led AMX to study a replacement engine for the CLM. They partnered with the Aster company, which had namely built generators for the Maginot Line. They designed a 4-cylinder 2-stroke engine of such power that I could only consider it as a convergent evolution to the Detroit Diesel 4-71 engine. This was of comparable volume to the R35's 85 PS 4 cyl 4 stroke gasoline engine.
The 1st prototype was presented at Satory on the 30th of October 1939, with trials set to occur at Bourges in 1940.
The tank faced typical defects that could be expected of a prototype at the time, that is problems with the engine, brakes, transmission and cooling system (the most explicit mentions are about the fan blades and tightness of the cylinder liners. In any case, the fate of this first configuration was already decided by the Keller program, which required heavier armor and a 47mm gun. AMX went back to the drawing board to develop the "series" variant, also called AMX 39. This simply increased the thickness of the front armor to 60mm and of the side skirts to 8mm instead of 5, lengthened the tank some more (adding an extra wheel in the process), and used a new turret. The latter was more reminiscent of the FCM 36 but still quite different, as it used a kiosk/turret extension with PPL episcopes for observation instead of a Gundlach periscope, and the 47mm and coaxial 7.5mm armament was protected with an external mantlet. The ARL 5 turret was also contemplated, with a weight of 2200kg, a 60mm-thick front and 50mm-thick sloped sides. The turret ring could still be fitted in the 1120mm-wide hole which was standard of all light tanks (yes, you could potentially fit it on a Hotchkiss H39 or R40).
Keller and the committee concluded that this tank did not meet the full specification due to the floor and side armor being below spec, and the power/weight ratio being a little under spec at 9.2 PS/t. The military engineer attached to AMX, Joseph Molinié, did however note that:
- weight will be inferior to the limit of 20 tonnes: 16.5 all things included
- The number of 47mm rounds is also above spec, 120 instead of 80
- Crossing capability is in excess of the program
- Tests of the tank loaded to 16.5 tonnes showed that it had the same performance as the R35 on road, and better offroad. That it runs on muddy ground at Satory in 4th gear, that trench crossings can be done in 3rd and sometimes even 4th gear, and that it extracted a H39 floor-deep in the mud in 1st gear.
Moreover, the engine obtained 85 PS at 1000 rpm on the bench, max torque of 70 mkg at 1200 rpm, and reached 2200rpm on the tank. The engine had been deliberately derated to 130 PS at 1800 rpm to reduce development delay. However, the 2nd prototype engine would achieve 155 PS at 1800 rpm and 160 hp at 2000 rpm.
Molinié rejected the creation of a new prototype to spec, on the grounds that it would take a full development phase of 1 year. At least for now, the AMX 39 would have to be accepted as is. The full spec variant, which could have competed for the "future" role for introduction in 1942, was to feature the required 60mm-thick side armor and thicker floor. A 6-cylinder derivative of the Aster 2-stroke would be made, delivering 230 PS. The extra armor would increase weight by 2 tonnes, and the longer hull and other mods would keep it within 20 tonnes. As one can see, the power/weight ratio would actually be improved to 11.5 PS/t.
However, it was a vast improvement over all previous light tanks and suitable in the interim, such that a small batch of 100-150 was being considered for starters. The decision for mass production would have to be made in April 1940 to allow the delivery of the first tanks in the Spring of 1941. We still do not know if that decision had been taken before the Fall of France, or if the AMX 39 would ever have been made (and in that configuration).
Overall, to put it in context, the AMX-39 would be most comparable to the British Valentine II/IV infantry tank. The latter enjoyed a 2nd crew member in the turret, a larger turret ring and greater upgunning potential (though the AMX didn't try to exploit the maximum size of the hull). It also already had the 60mm-thick sides, was lower in terms of turret and hull only, but wider and longer.
On the other hand, the AMX could carry a considerably greater amount of ammunition, some of which already was HE (unlike 2pdr for most of the war). The armor was better distributed (better floor and roof protection, fewer vulnerabilities at the rear and front), and welded from day one. The front is also thicker than indicated at first glance due to the plate being 60mm thick all the way, while the steeply sloped plate on the Valentine was 30mm thick (the driver's visor plate was also at least 65mm equivalent in the case of the AMX due to a 22° angle). The AMX suspension would probably also have performed better than the Valentine's on particularly problematic ground due to the better weight distribution compared to the 3-wheel bogies. The power to weight ratio would also be better for most of the war.
Characteristics:
Program
AMX 38
AMX 39
Valentine IV
Crew
2
2
2
3
Armament
1 47mm SA 35 gun, 1 coaxial 7.5mm MAC
1 37mm SA 38 gun, 1 coaxial 7.5mm MAC
1 47mm SA 35 gun (-14/+18° elevation), 1 coaxial 7.5mm MAC
1 2 pdr gun (-5/+20°), coaxial 7.92 BESA
Ammo capacity
80 47mm rounds, 3000 7.5mm rounds
Unknown
120 47mm rounds, 4500 7.5mm rounds
59 2 pdr rounds, 3150 7.92mm rounds
Armor
60mm basis - 30mm front floor, 20mm rear floor and roof
40mm plate thickness (except highly sloped rear plate at 30mm), +5 or 8mm side skirts, 17mm floor, 17mm hull roof, 20mm turret roof
60mm front, 40+8mm sides (50-60mm turret sides), 40mm rear (25mm for highly sloped rear plate), 25mm front floor, 15mm rear floor and hull roof
60mm front, 60mm sides, 10-20mm roof, 15-20mm front floor, 7 mm rear floor
5-speed gearbox with Cleveland steering (early project), prototype unknown
2 5-speed Wilson gearboxes, steering obtained by combining speeds of left and right track or by clutch/brake (4th speed must be moved closer to 5th)
5-speed Meadows, epicyclic, clutch brake steering
Width
1200mm internal hull, 1751.8mm hull with sponsons, 2110mm total
1260mm internal hull, 2170mm total?
1475mm hull (external), 2629mm total
Height
952 mm internal hull above fake floor, 1750 mm fighting compartment height (turret), 800 mm turret height, 2210mm total
897 mm internal hull above fake floor, 1667 mm fighting compartment height?, 1840 hull and turret height, 2227mm total height
1650 hull and turret, 2273mm total
Length
4280m hull only, 5034mm total
4515.1mm hull only, 5279 mm total
5200mm hull only, 5410mm total
Turret ring diameter
1120mm (fitting hole), 912mm at narrowest point
1120mm (fitting hole), 912mm at narrowest point
approx 50 inches
This question was discussed by military engineer Molinié of the AMX during the meetings of the tank design study committee throughout 1938. To sum up:
- The running gear on the R35 was problematic due to the front wheel being overloaded with no return roller to assist it, leading to frequent damage of the front suspension arm and the front of the tank digging in wet ground. This was combined to a low pitch track, low number of roadwheels, poor design of the track and underestimation of its required surface which, coupled to weight growth during development, caused the tank to have unusually poor mobility on wet ground.
The AMX running gear, with its high number of wheels could better spread the weight and resulted in a great improvement in offroad mobility, being able to use the 4th gear and climbing a 85% slope, and starting better during the winter. It also enabled an increase in weight of the tank, especially at the front, and as such it was essential for the later modifications.
- The engine could be uprated from 80 to 100-105hp without increasing its size through the use of improved cylinder heads. But the differential could not take the extra power and needed to be either increased in size, which would require a new differential/final drive housing; or better steels and manufacturing techniques had to be used, which couldn't be done by every factory.
- Beyond adapting the diff/FD housing to an enlarged differential, it needed to be improved so that the differential cover/maintenance hatch could be better set up to not be sheared off by projectiles, and to improve effective thickness which was 34mm on average and 32mm at the lowest when the tank was going down a 20° slope, thus not meeting the 40mm basis requirement. This is analogous to the WW2 Sherman getting a radically improved final drive housing in 1943.
- The floor of the tank had to be thickened to 20mm at least to resist potential AT projectiles hitting at 26° (tank going uphill) or simply against AT mines.
Molinié remarked that the R35 prototype ironically had a better differential housing with full protection of the cover, a better suspension, and a turret platform that was more conducive to good casting and good observation.
The suspension was eventually upgraded on the Renault R40, albeit much later than originally envisionned. The other upgrades never happened to my knowledge.
Use of high speed diesel engines - by 1st class Chief Military Engineer DUREAULT, director of the AMX on the 12th of January 1939:
The use of the diesel engine on fighting tanks has been recommended by the military technical services until November 1936. Currently the same services appear to have the opposite opnion and estimate, notably, that the diesel engine is more dangerous than the gasoline engine regarding fire risks.
Such a change in opinion appears unjustified to me regarding this particular point and doesn't account for the important advantages that the diesel engine also features. The following report intends to inform you of the information the AMX has on this question and to submit you the conclusions we can take from it.
It seems useful to consider separately and comparatively to gasoline engine, the characteristics of diesel engines pertaining to the equipment's conditions of use and those that pertain to strictly technical problems of design and manufacture.
I - Characteristics of the diesel engine pertaining to the conditions of use of armored vehicles.
These essential characteristics are those regarding fire risks and refueling.
A - Fire risk
Fires occuring inside tanks with gasoline engines usually take place in the following manner:
The initial cause is a backfire inside the carburettor, a short circuit, the introduction of flammable liquid on the louvres, projectile effect.
The start of the fire results from the inflammation of the gasoline vapors which form beyond 15°C.
The fire is then sustained and spread by unprotected combustible materials inside the tank like electrical wires and oil depots on the floor.
Fires occuring on railcars and trucks equipped with diesel engines are of 2 types:
a) by the fuel: a leak of diesel spread to electrical insulation. A short circuit occured, heated up the fuel, and then ignited it.
b) by soot: the exhaust is installed under the vehicle, so soot deposits on the walls of the muffler's piping; some also adheres to the hull. Soot that hasn't been removed early enough (every 500 service hours according to specialists) forms a crust that can heat up and burn due to exhaust gases and excess air evacuated by the exhaust. The incident usually remains restricted to a "chimney fire", but flammable material below the tank (wood, canvas) can be ignited.
The following conclusions can be made:
Diesel fuel removes the accident caused by backfire.
Short circuits caused by diesel fuel appear to be less serious than those caused by mechanical accidents or deterioration by greasing oil, and the same remedies to the latter problems will apply to diesel.
Regarding soot depots, maintenance every 500 hours doesn't appear to be an obstacle for tanks. Moreover, poorly tuned gasoline engines often cause the same problems, and these incidents are less dangerous for tanks which usually do not carry flammable material near the exhaust pipe.
But the main property of diesel is that it does not create vapours below 80°C (15°C for gasoline). This property is of the highest importance as it is an obstacle to the spread of fires. It is strange that this property appears to be the reason for the current critics "diesel stays, gasoline boils off".
Without arguing about whether vapours are more dangerous than the fuel staying on the floor, it seems easy to answer this objection: greasing oil depots are themselves as dangerous and more important. Maintenance done regarding this will be just as valid for diesel.
The current protection for fuel tanks might need to be changed but it is worth saying that it is far from perfect on current gasoline fuel tanks and that, here too, a study is necessary.
B - Refueling
Two facts have to be noted:
1) The economy of fuel in the case of the diesel engine for a given range is ca. 30%.
2) 100 kg of cracked diesel give 60 kg of gasoline
To refuel 10 45-light-tank battalions for a range of 100km, 38 tonnes (minimum, on road) of gasoline and 27 tonnes of diesel will be required.
Given the current conditions, the quantity of diesel produced by distillation of petrol will be likely too great in case of war. We would thus have to convert it into gasoline through cracking: 100 tonnes of diesel would give 60 tonnes of gasoline sufficient to refuel 700 light tanks over 100km; the same 100 tonnes could refuel 1600 diesel light tanks for the same range.
The AMX doesn't have all the elements of the problems, but these 2 facts appear sufficient to show that diesel engines would certainly be welcome in wartime.
II - Technical characteristics regarding the design and construction of tanks
1) Power
One has to obtain the greatest power output in a given volume. It is mainly the height and width of the engine which condition the size of the hull and running gear. The weight of the latter organs has been of ever greater importance, especially the hull. The diesel has the advantage of being viable as a 2-stroke engine; in such cases it is possible to obtain 130 hp in the same volume as a 100hp gasoline engine at the same rpm.
It seems even possible to obtain the necessary power excess which always is lacking, either for performance or for durability.
Wear of tank engines is a well-known fact, and the air filters are not the sole cause. Too often the engine runs all the time at almost maximum load at max rpm with prolonged spikes at full load at maximum torque. No common automobile engine is designed to work in such conditions.
2) Average speed
The torque curve of the diesel engine is flatter than that of the gasoline engine. Maximum torque is close to torque at max rpm. Thus, average speed is increased (by 20% on a Char D2 tried at Satory with a diesel).
3) Fuel tanks, range
For a given fuel tank size, the range is increased by 40-50% with a diesel engine. We can thus obtain the required range far more easily than with a gasoline engine, reduce the always excessive size of the engine bay, give more room for certain assemblies...
III Conclusion
1) The diesel engine deletes fire risk caused by gasoline vapours
2) The new risk that we associate to it is of little importance compared to similar risks that exist in a poorly maintained or designed tank.
3) It has major advantages regarding refueling.
4) When done as a 2-stroke, it can provide greater power density
5) In 2 or 4-stroke form it can increase average speed by 20% and extend range by 40-50%.
The main objection is that diesels (especially the 2-stroke) are rare. We can only regret this situation, but while it is mandatory to continue studies of gasoline engines to not delay the deployment of new tanks, it seems fair to question the current critics and to encourage the too rare high speed diesel engine manufacturers.
On to the 2nd entry into the infantry support tank program, the Char de 16 tonnes Renault DAC 1:
History:
This tank has been extremely obscure, at least until I dug up the review of the project by the tank study committee in the archives recently. More is to come at a later date...
The project started in late 1939. Renault also decided to move away entirely from the R35/40, but nonetheless capitalized on proven and known components, which the committee liked as it would be easier to put into production.
The DAC 1 used a simple hull with welded rolled steel plates, much like the AMX 38. Renault used a longer derivative of a running gear which it had designed concurrently from the AMX for the R35. It was similar and offered much the same benefits, but deemed apparently a little worse (heavier). It was also under consideration for retrofit on existing R35s, as unlike the AMX running gear, this could be easily installed in workshops.
The powertrain was the highlight of the project. It used an inline gasoline engine of 180-200hp which could use normal army petrol. However, it was mounted transversely rather than longitudinally with the gearbox sitting in the side of the hull, much like the Soviet T-44/54. This feature which was present on a few French projects at the time allowed the engine compartment to be shorter.
Additionally, the DAC 1's hull, contrary to previous French designs of this weight class like the D2 and S35, was advantageously lowered to an overall height of 1100mm rather (usually over 20cm lower than the previous two tanks), closer to the "normal" size for efficiently designed WW2/postwar tank hulls. This effort in minimizing the size of the hull is the reason the tank could carry the full 60mm basis of armour without exceeding 20 tonnes, while a Somua or D2 would have reached 25 tonnes this way.
Unlike the AMX 38, the DAC 1 carried the APX-4 turret of the B1 Bis, and thus could use a somewhat wider standard of turret ring. As such it had the potential to have a somewhat more serviceable turret than even the improved 47mm light infantry tank turrets.
The crew was also of 3 men, a radioman sitting beside the driver, with doubled up controls to replace him when fatigued. The radio was also installed between these 2 crew members and accessible to both, allowing useful redundancy. However the committee preferred that the crew return to 2, freeing space (notably for extra fuel). Overall, the project was not suitable as a stopgap due to it being too early, but it was perfectly suitable for the future infantry support tank program, as long as the thickness of the floor is increased and its method of assembly made more resistant against mines.
More will be known in 2025 after further research. But overall, this tank was a very remarkable design by the standards of Renault which had been previously known for being overly conservative. One can only imagine how it affected work on the G1R battle tank, the design of which we do not know about after 1938. Though the "to-spec" AMX future infantry support tank could have competed very well against it with its powerful diesel engine, the DAC 1 had some notable advantages such as speed and a bigger turret ring. This also held against the Valentine.
Characteristics:
Program
DAC 1
Valentine IV
Crew
2
3
3
Armament
1 47mm SA 35 gun, 1 coaxial 7.5mm MAC
1 47mm SA 35 gun, 1 coaxial 7.5mm MAC
1 2 pdr gun (-5/+20°), coaxial 7.92 BESA
Ammo capacity
80 47mm rounds, 3000 7.5mm rounds
91 47mm rounds, 3900 7.5mm rounds
59 2 pdr rounds, 3150 7.92mm rounds
Armor
60mm basis - 30mm front floor, 20mm rear floor and roof
60mm basis, 24mm floor and roof
60mm front, 60mm sides, 10-20mm roof, 15-20mm front floor, 7 mm rear floor
Engine
10 PS/t
180-200hp placed transversely (possibly I6)
138-165 hp GMC 6004
Top speed
25 kph
30-35kph
approx 25 kph
Minimum speed
2 kph at max torque
2,5 kph
Offroad speed on dry plowed ground
13 kph
Range
8 hours
6-8 hours (400L), fuel consumption 65L/hr
Trench crossing capability
2 m
2,2-2,25m
2,36m
Wading/fording height
1 m
1,05m
0,91m
Ground clearance
40 cm
40 cm
41 cm?
Climbing capability
0,8 m
0,8m
0,91m
Steepest slope
100%
45 degrees
Max weight
20 t
18-19 tonnes
16,5 t?
Ground pressure
0,8 kg/cm² not to exceed 1.5 kg/cm² anywhere
0,75-0,8 kg/cm² not to exceed 1.05-1.5 kg/cm² anywhere
>0,72 kg/cm²
Observation devices
PPL episcopes and Gundlach periscope
PPL episcopes and Gundlach periscope
Sprocket
Rear
Rear
Access
2 doors (driver and turret), 1 escape hatch
2 doors (driver and turret), 1 escape hatch
Starting
Mechanical and electrical
Suspension
Renault small wheel type with 10 wheels+2 elastic wheels at the front and 1 elastic wheel at the rear
Triple wheel bogies, 356mm track width
Transmission
6-speed preselector gearbox, differential with Lockheed hydraulic control, speeds per gear: 2.5, 4, 7, 12, 19 and 30kph
I am putting a translation of a report on French testing of anti-tank mines here before I move on to the big chunk that is the B1 Ter. This gives context on the rationale behind the required floor armor values:
Report of the meeting on the 28th of February 1940 of the tank floor study committee:
The discussion has been mostly technical. Its objective was to determine the measures to put in place for tanks yet to be built and existing tanks in order to reinforce the protection provided by tank floors against Tellerminen explosions, mostly to protect the crew.
Experiments done at BOURGES led us to the following conclusions:
- It is impossible to save the tracks and running gear of a tank from a Tellermine explosion.
- It is possible to protect the crew. A 20mm-thick plate is required. However this thickness offers only a small margin of security.
If the mine charge is greater than that of a Tellermine, or if the explosion distance between the mine and the floor is less than the 26 cm measured in the experimental conditions, then the security of the crew may not be guaranteed with certainty.
In the current state of our knowledge, it is advantageous to use monobloc plates rather than overlapping (spaced or stacked) floors.
Electrical welding, as long as the floor is braced against the tank hull in the direction of the explosion, seems preferable to fixation with small diameter bolts (10-15mm). It is not known how 40mm bolts would perform.
Finally, in the case where the main organs of the running gear are not independent from each other, the running gear beam must not be added on the hull, but must be instead consolidated with it.
Général DESMAZIERES remarks how limited our experimentation means are. It is how the experiments have been performed on real tanks (R35, H35, SOMUA) to their detriment and therefore, the experiments have been necessarily limited (author's note: to avoid the loss of the tanks), and their conclusions do not provide all the information it would have been desirable to obtain. He deems the creation of an experimentation workshop necessary (such a remark has already been made following trials of anti-mine equipment).
All the members of the commitee agree, but no organisation or service represented deems itself qualified to handle such a workshop. This question is usually in the domain of the Armament Ministry, which seems currently overwhelmed. But it interests the War Ministry. An intervention of high command with both ministries could be welcome.
Considering the results obtained at BOURGES, and the fact we cannot indefinitely upweigh the adopted tank models, the committee has the following recommendations:
A/ Measures to put in place for tanks to build (infantry support tanks and tanks of superior models):
- AMX: set floor thickness to 25mm.
- R35, H35, H39: study the realisation of a floor of 25mm maximum and 20mm minimum thicknesses (only required for the forward part of the floor) starting from the N th production tank (N to be determined). This thickness is currently 13mm, so the increase is great.
- FCM: no change as the floor is already 20mm thick.
B/ Measures to put in place for tanks currently in service:
- Hocthkiss: the floor of these tanks being fixed by bolts, unbolt the plates and replace them with 20-25mm plates, with the fixation method to be determined (welding, 10-15mm bolts, 40mm bolts). This operation will likely require the set up of a factory.
- Renault: The floor of these tanks is welded. The reinforcement will be difficult to achieve and moreover this model of tank has no weight growth reserve (mostly the R35). Study the application of a second 20mm thick plate or partial plate under the forward part of the existing floor.
The story of the B1 Ter far precedes the Keller program and, in fact, some of it starts as early as September 1934. At this point in time, France had extensively tested basic B1 prototypes and were about to order one full battalion of it. The development of new tanks of the Char B family, the B2, B3 and BB, had also been started in 1931-32.
A question arose to increase the armor of the B1 to 60 mm to guarantee full immunity to the 25mm AT gun which had been tested and adopted and generally improve the tank's protection against proper antitank guns. 2 options were initially studied:
- simply adding additional armor plates where needed to increase the armor to the specified level while uprating the engine from 180 to 250hp (in reality more will be achieved) with otherwise no changes.
- create a new tank with 60mm-thick plates and with other improvements.
The B1 Bis which was finally adopted corresponded to an hybrid of the two solutions as it used 60mm-thick plates and was a new-build, while being otherwise merely a maturation of the B1 with no major changes.
The modified B1 project with deeper changes was studied on the following basis:
A/ Assemblies coming from the B1
Engine: Current maximum output, 280 PS at 1900 rpm, used on the B1 at 270 PS at 1800 rpm. Can be pushed to 290 PS by increasing the compression ratio and slightly increasing fuel consumption.
B/ Assemblies coming from finished studies
Motion reverser
APX/ARL Gearbox with two secondary shafts
Controls and brakes
C/ Assemblies to study
Cooling system
Suspension springs
Interior layout
+-3° horizontal traverse for the 75mm gun
100 kg was saved on the suspension, 250 kg on the gearbox and brakes, 150 kg on misc parts, saving up to 500 kg.
The armor of the vertical parts was increased to 60mm except for those protecting the running gear (25mm) and 25mm-thick horizontal parts (floor, with 20mm below the engine bay/roof), increasing weight by 3.5 tonnes (2.6 tonnes due to the uparmoring project + protection of the tracks and modification of the rear of the tank). Total weight growth was thus 3 tonnes (due to weight savings.
A new gear ratio for 1st gear would allow the tank to retain its current slope capability. Speed would not be changed, so rigidity would be designed as required and the running gear would handle the extra weight.
Even before I obtained these letters, a project with the codename Char BL and its plans were found, dating from January 1935 and featuring a hull with revised, increased ammo stowage, horizontal hull gun traverse, thicker armor and armored tunnels for the upper run of the track. Now, I can confirm that this Sept 1934 project is the start of the BL, and that BL and B1 Ter are the same thing (see part 2 of my Vincennes archives photo albums in the relevant section on B1 Ter/BL).
More is said on the Char BL (B1 Ter) in a letter from February 1935:
"In parallel to the drawing of the plans for an uparmored B1, I started examining the possibility of bringing the armor thickness to 60mm as a single plate. This led to a project which would retain certain elements of the B1:
- Engine uprated to 300 PS (trials done with a special carburettor on the current engine)
- Clutch designed for 300 PS
- Naeder hydraulic steering system or motion reverser
- running gear, save for parts which would have excessive wear
- Driver's cabin, turret and 75mm semi-automatic gun from the Bourges establishment. It allows better layout of the tank.
- Ammunition stored in accessible lockers rather than spread all around in the tank
- Sharp increase in 75mm ammunition capacity (131 with rubber springs, or 93 with Weydert washers).
- Cooling with horizontal radiators which move the louvres to the top of the hull, remove a weakpoint and resolve the problem of waterproofness below 1.5m.
-+-5° horizontal traverse for the gun instead of 0°
The project intends to use the APX gearbox with two secondary shafts which increases the length of the fighting compartment by 222mm, and will be tested in March and April 1935 in the n°101 B1 prototype.
This project could be done in late 1935 by modifying the current 101 prototype, if I can get the special credit for:
- the manufacture of the armor plates for the hull
- the purchase of radiators and a special command for the fans
- the manufacture of a certain amount of running gear parts and replacement of the track pads
- manufacture of a mount for horizontal traverse
A new batch of B1 tanks ordered in 1936 could be built without issue following this project which could be finished easily and would allow us to wait for the end of the B2's development. The studies done by the state services (APX) would allow us to get out of the ESTIENNE consortium agreements and call on the competition of other manufacturers than the signatories of the 1921 and 1930 agreements.
The resulting weight would be 30.3 tonnes (given the weight saved on the gearbox). If the width was increased to 2.75m, the exterior side armor plates could be partially inclined and thickened to 75mm which would increase weight from 1 to 1.5 tonnes.
Speed and autonomy would be unchanged at 27 kph and 12 hours.
Transforming the current 101 prototype would cost 400 000 francs.
Development of the B1 Ter was done under the auspices of Military Engineer LAVIROTTE (from the ARL Rueil arsenal, an annex of the APX) and Lieutnant BRUNO of the 51° heavy tank battalion who regularly visited Rueil and was part of all B1 testing detachments, and perfectly knows the tank. I suspect Lavirotte is behind the "Char BL" designation, which would mean: Char B-Lavirotte.
To sum up: As of early 1935, one can conclude from these documents that the B1 Ter was originally intended as an alternative to simply adding armor plates to the B1 and as a more advanced follow-on to the B1 or B1 Bis while waiting for the Char B2, incorporating improvements based on studies from the APX/ARL design bureaus and offshoots from the B2/B3/BB development programs (the horizontal traverse from the main gun). At this point in time, the armor might still possibly have been 60mm instead of the 75mm characteristic of the B1 Ter we know. Weight was closer to 30 tonnes (32 with thickened side armor), compared to 27 for the B1 and a bit under 30 for the B1 Bis.
In reality, things would change quite a bit in 1935, with a letter from the 2nd of August 1935:
"By note n°938 10/MMA from the 16th of April 1935 the Army Headquarters made it know that, in agreement with the advice expressed by the Consultative Council for Armaments, the study program regarding the battle tank would now involve:
- the abandonment of the studies for the B2, B3 and BB tanks
- study of a tank armored at 75mm derived from the B1,
- the search for a new more modern battle tank, specially designed to obtain the maximum protection compatible with a weight of around 35 tonnes.
The study of the tank derived from the B1 will be given to the APX. The prototype will be presented in December 1935.
Regarding the study of the 2nd tank, Army Headquarters deems that, for this more long-term solution, it would be interesting to move away from the characteristics of existing vehicles.
This modern 35 tonne tank was essentially a more modern take on the B2 with focus on thicker armor, to be obtained with efficient shapes.
The B1 Ter thus moved on from a simple stopgap until B2, now becoming the short term replacement for the B1 Bis. The core objectives were to:
- improve the design
- move away from the ESTIENNE consortium agreements
The ESTIENNE agreements are agreements dating from 1921 which said that production of the Char B would be entrusted to only 5 manufacturers, with production of the tanks spread between them and with each manufacturer producing specific parts to distribute to all the others:
- FCM
- FAMH (Saint-Chamond)
- Renault
- Schneider
- Delaunay-Belleville
These agreements had been intended to create a large industrial complex for battle tank production much like had been done in WW1 for the Char FT and to have a design using the best features from all the competitors. Unfortunately, by 1934 it was clear that gatekeeping production at a few select manufacturers prevented competition and thus kept prices excessively high. Moreover, production of parts was uneven between the different manufacturers and caused severe delays and low production rate.
FCM said it could assemble 10 B1s per month by March 1936, but due to insufficient production of parts by other manufacturers (Renault could only build up to 5 engines per month), only 3-5 per month was achieved for much of the prewar period and 10 was only reached in 1939 shortly before the declaration of war (albeit with changes in the makeup of the consortium). These issues are why the Army sought very early on to abandon the agreements, which it could do if the tank now incorporated parts from a state arsenal like APX/ARL.
From prototype to serial production:
The short development timeline the Army desired was never achieved. Here are snippets from a postwar article by Engineer LAVIROTTE himself:
"Without sufficient funding, it was not possible to build a special prototype to try the new gearbox. As a result it was decided to use the hull of B1 tank n°101, loaded up to 33 tonnes and uparmored to 60mm. It received the gearbox with two secondary shafts and an improved running gear. After satisfactory trials of the gearbox, a prototype was constructed at the ARL . It was delayed due to strikes at the components' suppliers : SOMUA for the machined armor plates and FCM for the running gear and floor (with trouble due to the flattening difficulties for the 40mm-thick running gear side armor plates at the IMPHY steel works).
The experimentation of the prototype B1 Ter getting increasingly longer following incidents concerning the gearbox due to failure of the needle bearings, no decision could be made regarding a future batch. But the prototype was made of disparate items, either new or from the n°101 tank (sprockets, linkages) ; its construction had been affected by the period of strikes and of less controlled work. On the other hand, trials based on only one prototype, were it satisfying, didn’t mean much. As, moreover, the trials committee of the Infantry restarted trials after every incident, without taking account of previous trials, they could be done with a running gear which had accumulated 1500km, and 3500km for parts of the gearbox. Therefore, it was decided to build 3 tanks to prepare the batch to replace the B1 Bis. At the same time, the design bureau of the ARL was preparing a program for tank engines with carefully defined characteristics, for outputs of 180, 350 and 500hp (same components, different number of cylinders).
A tank was made at the ARL to update the plans of later manufacture, to verify assembly and eventually fine tune before construction of the two other tanks. The assembly of the 2nd one was given to FIVES-LILLE at Lille, and the 3rd to FCM at Marseille.
The three sets of running gears and floors were ordered from the FCM save for all mobile assemblies, given to DEVAUVILLE.
The sloped armor plates were delivered by the MARREL steel works and were machined by CHAVANNE-BEUN, the cast armor was provided by the FIRMINY steel works and the gearboxes were ordered from BAUDET-DONON-ROUSSEL. The serial production blueprints finished in June 1940 were evacuated to Saint-Nazaire.
The tank built at RUEIL was trialed on a testing ground. It was fitted with a gear drive for the NAEDER ; fine tuning could not be done at RUEIL as German advance required retreat to Saint-Nazaire. The 3 gearboxes were bench tested at RUEIL, equipped with their NAEDER steering system. MESSIER hydraulic commands, articulated CORSET commands and blade/leaf spring BROUILHET commands were bench tested. Only the MESSIER type was retained. A commercial navy type insulation of the exhaust pipe with magnesia paste gave excellent results.
Saint-Nazaire trials : The 1st prototype, the tank built at ARL and the unfinished FIVES-LILLE one (to be finished by FL personnel) were sent to Saint-Nazaire at the PENHOET works late in May 1940.
The trials of the ARL vehicle were initially stopped due to incorrect alignment for gear changes and defects of the NAEDER device ; after addition of an extra return level to the main shaft for command of the NAEDER, of the rear cover of the tangential screw of the steering differential, and the replacement of the NAEDER, satisfactory trials were done on the Loire works grounds (ACL) : good run.
The 3 tanks, when finally completed would have been gathered at the COETQUIDAM base and would have constituted a group which would have been given to the Command with military personnel from ARL.
They were loaded on the 17th of June at the ACL on the Médecin Principal « CARVIN » ship of the WORMS company with 2 380mm guns and 2 propellers from the Jean Bart battleship.
The ship was torpedoed next to the opening of the Gironde river and, just like the amphibious tank sunk in the Erdre at NANTES, the 3 B1 Ter ended their career in the Atlantic, the only remaining specimen being the tank in construction at FCM at Marseille."
The prototype 101 loaded up to 30 or 33 tonnes and only equipped with the new APX gearbox did trials at the MOURMELON proving grounds in 1935-36. The extra weight actually corresponded to the B1 Bis program. Funding had been insufficient to test both 60mm of armor and the gearbox separately. Luckily it had no consequences and showed the B1 Bis was viable, while indicating the first gear for the new gearbox would have to be modified to maintain good slope climbing capability at a heavier weight. Owing to the disruptions of 1936, it was not until 1937 that the B1 Ter prototype was ready, and not until December that it went to the BOURGES proving grounds. The n°101-based B1 Ter was thus tested from 1938 to October 1939 at the various proving grounds of MOURMELON, BOURGES, RUEIL-FONTAINEBLEAU, and SATORY.
For much of its life, this B1 Ter caught little attention from the Army which focused on the then-promising G1 battle tank program (a program I will talk about elsewhere and later), and limited funding meant they had to make do with a single prototype with parts from one of the oldest B1 prototypes, which were not necessarily suitable for the weight. Having only one prototype which was itself not necessarily as reliable as a completely new-built prototype resulted in a long development period, which prevented the B1 Ter from ever replacing the B1 Bis in peacetime.
When the future of the 1 program became more uncertain and tensions rose, 3 modern prototypes were finally allowed in 1939, to be delivered in May, June and July 1940. It was decided that if the B1 Ter was to be built, it would have to be after the 2nd mobilization order for the B1 Bis, meaning after the 1178th Char B, in March 1941, to minimize disruption of production. The decision to put it in production or not would thus have had to come in July 1940, based on May-June testing of the Rueil prototype.
As we know, this never happened. We will never really know if the B1 Ter would have been produced at all (though judging by the improvements both in performance, reliability and quality of life, this was very likely to be accepted for mass production), nor if it would have been made at the time and in the form that we know.
The next posts will delve in greater detail into the design of the B1 Ter and the trials of the 101-based protototype.
B1 Ter technical overview:
Most of the overview is from the same postwar article by LAVIROTTE and some of it may be less reliable due to the time gap. Moreover it is hard to know what was part of the original B1 Ter prototype and what is part of the modern pre-production prototypes.
The tank then possessed the following characteristics :
Engine:
Type B1 Bis, 4-stroke 6-cylinder inline Renault reinforced aircraft engine with 140 mm bore and 180 mm stroke, 16.5 L displacement,
307 PS at 1900 rpm, maximum torque 199 m.kg
Cooling system:
New type Grouvelle-Arquembourg radiator, monobloc, placed horizontally and elastically fixed to the chassis with REPUSSEAU shock absorbers ; a steam separator (with marbles/ball bearings) allowed the circuit to function no matter the tank’s orientation.
Helical RATEAU fans, fixed on the radiator and driven by TEXTROPE fan belts.
Relocating the cooling system to the top removed a potential weakpoint in the side armor, but also allowed the tank to ford a 1.8 m deep river instead of 1.05 m like on the B1 Bis. Additionally, another report indicates that the single Bombyx fan drive belt would have been replaced with a more durable setup with three trapezoidal belts, which may have been planned to be introduced on B1 Bis as well.
Accessories :
- Recovery tank, can be emptied in case it freezes, can be vented to outside air.
- Circulation and recovery pumps,
- Engine oil heat exchanger of the LAMBLIN type
Fuel supply:
Three tanks with the form conforming to the hull, the main tank taking the place of the original B1 radiator. 500 L capacity instead of 400 L on the B1 Bis to make up for the increased consumption driven by the increased weight.
Unrelated to the B1 Ter project, it was recognized in 1939/40 that the actual autonomy of a B1 Bis was of just 5 hours or 5 hours 30 minutes, instead of the required 8 hours. Towards May, it was decided to adopt 2 solutions to this problem:
- accept reduced free space and restow the ammunition from the engine bay to under the floor of the fighting compartment (much like other WW2 tanks), to install a new 200 L fuel tank.
- modify the hull rear to install a 200-250 L fuel tank. A tank with this modified hull exists, it is the n°505 turretless tank sent to combat in June 1940, with a characteristic triangular rear hull.
Both modifications when applied to a B1 Bis would increase range to almost 11 hours in theory. It is likely that something similar would have been done for the real serial production B1 Ters, though the already present extra 100 L would probably result in a reduced gain from the modified hull rear. Range would still be well in excess of 8 hours and closer to 10.
Clutch: B1 Bis type.
Gearbox:
- Gearbox studied by the ARL and built by the BAUDET-DONON-ROUSSEL company. This gearbox was designed for the torque of the 300 PS engine and was 222mm shorter than the B1 Bis gearbox, allowing a longer crew compartment.
This gain was obtained by :
- Using two secondary shafts
- Mounting some shafts on needle bearings
- Replacing some bevel gears with globular screws/globoid worm gears
While the engine was driving the primary shaft still in gear, the first secondary shaft ended by a globular screw was used for the first, second and third forward speeds and the reverse gear (with an intermediary shaft), the second secondary shaft was used for the third and fifth forward speeds and drove the main differential via a bevel gear. The planetaries and satellites were of the spur gear type as it was easier to build than conical/helical/bevel gears. The auxiliary differential driving the steering mechanism was driven by a globular screw. The different gear ratios compared to the B1 Bis gave slightly greater speeds in 1st gear and reverse, a drawback which was fixed later for the 3 pre-production tanks.
Maximum speed at 1800 rpm (kph)
B1 Bis
B1 Ter prototype
B1 Ter preproduction
Gear
3.02
3.64
2.8
Forward 1
6.65
6.49
6.49
Forward 2
11.19
10.86
10.86
Forward 3
19.3
17.23
17.23
Forward 4
27
26.51
26.51
Forward 5
3.02
4.48
4.48
Reverse
Apparently the higher reverse speed of 4.5 kph was not changed again, so the B1 Ter would have been a little faster here but slower in all other gears when using the 300 PS B1 Bis engine.
The main objectives of the APX gearbox were to reduce length (by 222mm), weight (by 250kg), and cost. The needle bearings always had issues and eventually only roller bearings were used.
- Braking through band brakes (B1 Bis used shoe brakes)
Running gear :
- B1 Bis type track
- Reinforced B1 Bis type running gear, deletion of the box (housing), each skid being welded to a steel plate welded on the armor or the internal flanges ; the removeable armor plates fixed on the B1 Bis running gear box were replaced by a single plate.
- Reinforced B1 Bis type suspension.
- Centralized lubrication system driven by the engine, providing constant lubrication of the running gear’s skids and return rollers ; the device studied by the RELLUMIT company contained a tank, a pulsation pump for the grease tables with calibrated adjustments, and a piping network. It was trialed for 2 years and considerably reduced skid wear. The oil overpressure automatically unclogged pipes clogged by mud or dirt.
Other than a simpler and stronger structure, the main improvement to the running gear was simplified maintenance and reduced wear due to the centralized lubrication system.
Protection:
On request of Général VELPRY, tank inspector, the side armor plates were sloped at 25°, which only brought increased protection for specific positions on the ground.
Studies performed by the General Engineer DESMAZIERES at the central laboratory determined equivalency curves for thicknesses between 60 and 100mm, taking account of the orientation of the tanks on the ground (author’s note : protected arcs) and armor plate slope. Armor sloping gave the tank a more aesthetic and compact shape, but particularly complicated the layout. The HQ accepted the equivalency to 75mm of 70mm sloped at 25°. The number of plates was reduced to the minimum.
- Belly : The belly was 20mm thick (author’s note : 30mm per most other sources) and formed a welded assembly, bolted to the two running gear assemblies. The latter were armored externally by a 40mm-thick plate (author’s note : other sources say this was increased from the 25mm of the B1 Bis), and internally by 3 plates welded together and a 45° spacing/bracing plate supported by the belly and the internal side plate. This spacer and the external armor plate were pierced with holes covered by hatches to allow the removal of roadwheel bogies ; the belly was fitted with maintenance hatches for the engine and the gearbox. The rigidity and protection against mines and shells (deletion of many armored hatches and most of the bolts) were greatly superior to the B1 Bis, in particular thanks to a 15mm stiffening plate angled at 45°.
- Roof: Apparently 30mm instead of 20mm to improve protection against air attacks.
- Front : The layout of the gun mantlet/mask allowed the deletion of the B1 Bis’ front spacers, which offered a notable advantage for obstacle crossing. The frontal plate was sloped at 45° and 60-70mm thick (author’s note : exact value is unreadable but French equivalency curves were particularly overkill for a tank on flat ground so actual protection would be in excess of 70mm). Rear armor was 60mm vertical.
- Louvres/intakes
The louvres were made of welded blades, the number and shape of which had been determined by trials on a B1 Bis (ballistic and cooling trials). The exhaust was laid on the 25mm-thick hull roof and the air intakes were on the sloped rear area, balanced by a spring. Two other louvres allowed the cooling of the engine exhaust pipe/collector ; a protector was placed on the opening over the CHOBERT radiator.
- Track tunnels
The track tunnels (40mm thick vertically, 20mm horizontally) were fitted with maintenance hatches. Evacuation ports with armored covers (1 right, 2 left) were intended for mud evacuation. They were designed to reduce risk of tank stoppage due to damage to the upper run of the tracks from enemy fire, and reduce detection from aircrafts. They could be removed in case of clogging by mud.
- Side door
The side door was 70mm thick and followed the profile of the transversal section of the tank (the diamond side armor plates) ; it was articulated on the lower part around an horizontal axis, and possessed two eyes to mount chains linked to two spring equilibrators via return pulleys, the articulation points being chosen so that the movement curves of the door and equilibrators were almost superposed. Closing was achieved by 3 locks driven simultaneously and eccentric with cranks and break-even points, the length of which were adjustable to obtain desired pressure of the locks on the sloped planes. Opening of the door was normally done from the inside, or from the outside after having removed an obturator.
The B1 Ter and B1 Bis were also meant to receive a semi-collective protection system against combat gases.
Arrangements:
1) Upper lateral beams/girders
The reduction in the number of the sheets on the upper side of the belts and sheets linked to the roof done on the last B1 Bis was continued and the entire assembly was replaced by a single steel 18/8 beam ; a greater rigidity of the hull and some weight reduction was obtained. Armor plates were fixed to the upper lateral beams at the front and rear of the left beam and at the rear of the right beam.
2) Main frames
The hull was rigidified by the central bulkhead and by two frames, one in front of the front springs and one behind the rear springs.
The double wire installation (unlike the B1) was powered by two SAFT cadmium-nickel batteries of 24 Volts and 320 Amps.h, which could be used in parallel for starting thanks to a relay, or made independent with one charging and one idle and powering the radio receptor to facilitate reception. The metallic shrouds were deleted except for the starting circuit ; the LABINAL voltage regulator possessed a self and capacity group to act as filter on the generator ; the charging circuit no longer emitted noise. The electric pannel comprised a box containing the usual equipment (exept the cut-outs/breaker switchesand their filters), easy to install.
The new electrical equipment largely solved two problems with the B1 Bis:
- the need to use the engine most of the time to charge the battery. The new system could operate longer without the engine.
- interference. This would have notably improved signal quality and range.
Armament:
The prototype had:
- A 75mm SA 35 gun with +-5° horizontal traverse and a fixed 7.5mm machinegun in the hull
- A 47mm SA 35 gun and a MG in the APX 4 turret. The APX 4 was to be replaced by an ARL turret.
75mm SA 35 gun mount:
The 75mm gun was held on its mount by two horizontal trunions ; it held a sector gear moving with it, driven by a worm screw fixed on the mount, itself driven by a bevel gear transfering the movement of the horizontal traverse control wheel placed under the driver’s wheel. The aiming sight was fixed on the mount to allow the driver to follow the target, the lateral aiming angle being small enough that the sight’s ocular didn’t move much. For vertical aiming, to follow the target in the sight, light was sent back to a prism which moved around an horizontal axis parallel to the gun trunions. When the prism rotated by X degrees, the light was deviated by 2X degrees. The angle the prism turns must be half of that the gun turns.
The improved mount with horizontal traverse not only featured a better sighting system, but was generally much more convenient for the driver who aimed the gun. Previously the driver had to turn the entire hull precisely to aim the gun which was fixed horizontally. Now, the demand on the Naeder steering system for finer aiming was reduced, reducing wear, fuel consumption and possibly increasing actual hit probability.
Ammunition capacity:
75mm : 90 (or 100 according to another source) instead of 74 in the B1 Bis
47mm : 30 HE, 30 AP + 7 in the turret (72 in the latest B1 Bis).
All stowed in alpax racks and spread around the fighting compartement and engine bay.
30 machinegun drums (4500 projectiles).
Turret:
The APX 4 was replaced by the ARL 2 turret, studied under the direction of military engineer DEVENNE by the FIVES-LILLE company.
It was comprised of :
- A body, shaped like a truncated hexagonal pyramid, formed of 70mm-thick rolled plates welded together, a slightly sloped 40mm-thick roof, an equilibrated door with mechanical command and a vision slit. This body was mounted on high efficiency ball bearings with no stapling of the turret to the hull roof
- Forged or rolled steel pieces fixed in the body for the openings of the weapons protected by external mantlets, covering them from all angles, and for the internal masks to stop bullet spall
- A monobloc, stamped hexagonal observation cupola containing 3 PPL episcopes and on the upper part a GUNDLACH periscope
- A 47mm gun and a machinegun aimed manually, the machinegun being independent from the gun and traversable horizontally to facilitate MG fire on the move.
- Aiming mechanisms
- Observation devices : a sight of the same type for each weapon, 5 PPL episcopes (2 in the body, 3 in the cupola) and a rear vision slit. The lines of sight overlap each over 50cm away from the turret walls at the front, and 1m at the rear.
- Ammo which is added to that spread in the rest of the tank (7-round ready rack, 2 drums of 150 cartridges, including 1 on the MG)
Turret traverse was ensured by a SAINT-CHAMOND-GRAMAT electric system with continuous speed, operated without effort by a hand lever, with the addition of two wheels, one to obtain slower speeds, the other in case of system failure. A limiter brought the turret back to its original position after gun recoil, which facilitated rapid fire and reduced recoil effort.
The rolling system was composed of
- A central crown with two races on which rested the turret ring
- Two external crowns with ball bearings in a single race each, the lower one on which rolling was done and the upper one in the roof which prevented the lifting of the turret. The gun was manually traversed vertically by a handle which also had the trigger (-4°/+18°)
The door rested 8° forwards when opened. Its opening and closing were particularly well done by special devices.
The late 1930s saw the French switching development efforts from fully cast turrets to welded assemblies of rolled plates and smaller cast elements, which increased plate resistance (higher hardness), though actual protection may not have changed that much due to the reduction in curved surfaces. This also simplified production, cast turrets having faced multiple delays in deliveries before. Additionally, these new turrets like the ARL 2 and FCM turret moved over to fixed cupolas rather than small rotating cupolas, which further improved simplicity, increased room and possibly reduced the risk of the entire cupola being sheared off when hit.
The ARL 2 appears to have been generally better furnished in observation devices, with possibly better and more overlapping fields of view (the APX 4 cast turret had fewer PPLs), albeit at the cost of the binocular sight in the APX 4 cupola. That said such a type of cupola was allegedly still referenced for the ARL 2. It seems that the electrical traverse system was also somewhat improved. Finally, the ARL 2 was apparently roomier and could store a 7-round emergency ready rack which facilitated the first few dozen seconds during engagements. The ARL 2 armored at 70mm would have weighed 3 tonnes instead of the 2500-ish kg of the APX 4 with 56mm.
Though notably improved over the APX series turrets, the ARL 2 (and competing FCM turret) did not change the interior turret ring diameter and remained 1-man turrets.
Modifications done after testing of the prototype Armor :
- Armor beak on the plates of the return rollers to protect their skids.
- New gun mask allowing better vision to the right side for the driver.
- Louvres : intake over the CHOBERT radiator, addition of louvres on the exhaust collector, exhaust
louvres done in 3 removeable parts on the same chassis.
- Driver’s cabin of the ARL type, derived from the mockup showcased in July 1938 before a special committee (Colonel PILLOT, Capitaine BESCOND, Capitaine LEBOEUF, Lieutenant BRUNO). Cast steel was replaced by 3 70mm-thick rolled plates, assembled with welding and lugs.
It was comprised of:
- A front face with a shutter with an upper horizontal axis, of double the size of the B1 Bis’ shutter.
The shutter was equipped with a slit holding a PPL periscope with a vertical field of view of 37° (+5, -22) and a horizontal field of view of +-34°.
- An emergency slit on the shutter which is covered by a plate as long as the PPL is used.
- A left side face with a PPL with the field of view limited by the gun mask (+5/-10° vertically, +-22,5° horizontally)
- A roof laid out as an access hatch and fitted with a panoramic periscope.
It is worth noting that the PPL was made of two parts, one light and easy to replace, the other removeable but heavier, invulnerable to small projectiles. Vision was possibly 3.75m in front of the tracks, 5.5m away from the left side of the tank, 10m away from the right side.
Engine :
The three tanks were equipped with 300 PS B1 Bis type engines. One was supposed to get Fleury type pistons (5.7 compression ratio), increasing power to 310hp and reducing specific fuel consumption.
These engines were meant to be replaced by 400 PS 12 cylinder square 130x130mm Renault engines (350 PS per another source, but likely 400) of 20 L, of which 3 prototypes were in construction and one on the bench as of the 10th of June 1940 ; or by 350 PS 6 cylinder 155 mm bore x165 mm stroke Renault engines of 17.6 L, of which 2 prototypes were built and on the bench, and one in construction.
The Vee engine was the only one planned but its study had been launched during a propaganda trip abroad by M. Renault. As he preferred inline engines, he stopped its construction when he returned and launched the study of the 6 cylinder engine. However, his orders were not followed and the main parts of the other Vee engines were machined in his factories, the rest being machined by the subcontractors of the ARL. Similarly, an engine was completely built and put to the bench. Limited to 2000rpm to use the gearbox of the 3 pre-production B1 Ter, they were to run at 2800rpm for serial production vehicles or the B40.
These engines were based on a program drawn by the ARL to obtain engines suitable for tanks with the following definition for nominal power :
- Maximum power in continuous operation at nominal regime : 9/10 of the maximum power at the nominal regime
- Maximum power : can be maintained for 1 hr at nominal regime,
- Power at maximum regime : 30 min on the bench at 115% of the nominal regime,
- Road power : Continuous service at 15% (115%) of nominal regime : 7/10 of maximum power.
- The regulator allowed to obtain full charge at nominal regime and reduce it automatically and progressively at maximum regime, to bring it to road power. Moreover, the engine was to do an overspeed test at 110% of maximum regime.
Though rather obscure, these engines at least indicate a move towards reduced stroke and a stroke/bore ratio closer to square engines, which means reduced load and the potential for higher rpm. It is also extremely likely, considering these engines were related to the ARL tank engine program, that they worked with Army 65 octane fuel rather than the aviation fuel used in the B1 Bis. This would have notably simplified logistics for the B1 Ter. This would also explain why the improvement in power per litre was rather modest compared to the much older B1 Bis engine. It is likely that durability, possibly ease and construction and maintenance were improved on these modern clean-sheet engines.
Fuel supply
Addition of :
- A starting pump
- Evacuation piping with an obturator
- Vents on the right-side fuel tank, and on the piping linking the two left side tanks on the upper part.
- 2 automatic RELLUMIT fillers on flexible upper piping linking the left side tanks and the piping of the right side tank
- 4-way tap/valve, carburetor, left and right AM pumps, pressure gauge
Modification of the collector with :
- 1 piping per tank
- Starting pump pipes leading to each side of the collector
The 3 spirobloc indicators were fixed on the protection plate of the right tank, the supports for the
tank being in fire-protected wood.
Gearbox :
Acceptance of all of the modifications done to the prototype, in particular the deletion of the needle bearings and trial on one of the gearboxes of the gear drive of the NAEDER system.
Clutch:
Redesigned to handle 400 PS.
NAEDER system :
- Pump drive with TEXTROPE belt, chain tensioner
- Interchangeability of detail parts of the entire mobile generator assembly (instead of the complete assembly) by acceptance of eccentrics and identical inclined front and rear cams
- simplication of the splined shaft, the gearbox player
- new drawer bearings
Running gear :
- Addition of 2 REPUSSEAU shock absorbers between the 2 trays of the forward and rear coil springs to reduce pitching
- Fixation of the skids by pins in holes of 2% of conicity and screws ; the mild steel wedges/chocks were retained to facilitate the machining made necessary to maintain the constant spacing of the 2 flanges ; the skids were no longer welded.
Return rollers :
Addition of a 3rd shock absorbing rubber stop after the helical spring and the 3 Belleville washers.
Arrangements :
The speed commands of one of the tanks were to be done by a MESSIER hydraulic system which had been bench tested ; the linkages were also deleted ; the ducts were fixed on the sides of the tank instead of the floor to improve protection against mines.
- Bulkhead in 15/10mm MARCHAL type sheet with a 2mm thick asbestos canvas, a 10mm-thick mattress of glass silk, 3mm of asbestos board coated in aluminium silicate powder, 8mm-thick cooling air blade, 2mm of asbestos canvas
Compressed air system
The brake command air supply with a tap driven by pedals of the gyroscope and different manholes was ensured by :
- 1 OERLIKON type compressor (1.3hp at 1000rpm) driven by two TEXTROPE fan belts mounted on the forward pulley of the engine
- 1 stainless steel tank of 40L with a purge tap and filter
- 1 cooler
- 1 de-oiler with its purge tap
- 1 regulator with safety vent and an expander
- 1 board with 2 pressure gauges (left and right brakes) and a double pressure gauge towards the gyroscope and the tank and its cylinder
- 1 dirt-catcher
Turrets :
2 ARL 2 turrets, one in armor steel and one in mild steel were ordered from FIVES-LILLE ; the FCM tank was to use a 37 FCM turret designed by this company, but 2 other armor steel ARL turrets were ordered as delays were expected.
Summary:
The B1 Ter eventually reached a weight 36.6 metric tonnes, which is why the original engine was no longer considered suitable.
It was no longer a simply uparmored B1 Bis with some other improvements, but a major redesign more akin to what the KV-1S was to the KV-1, for exemple. The armor had been significantly enhanced to a basis of 70-75mm but with many parts actually exceeding that protection level, making the tank near immune to the German 5 cm L42 tank gun and the 47mm PaK 36(t) which would have been in use or proliferated by Spring 1941, and notably more resistant than the B1 Bis to the 5cm L60 gun and potential use of captured French 47mm and 75mm guns or German medium velocity 75mm guns like the Krupp and Rheinmetall designs in development since 1936 (weaker than the PaK/KwK 40). On top of that, the crew would have been even safer in case of AT mine explosions, which would have been a major boon in any 1941 offensives combined with mine-clearing equipment.
The tank had also seen many quality-of-life upgrades and Reliability/Maintainability/Durability improvements, with improved observation capabilities for the driver and commander, easier use of the main weapons, more convenient use of the radio, and generally more durable and maintainable automotive parts. Some simplifications and greater use of welding could possibly also increase the mass production potential compared to the B1 Bis, helping satisfy the ever growing French appetite for the battle tank.
The new engines also possibly promised much simpler fuel logistics, and could restore the original mobility of the B1 Bis or possibly even improve on it. While the 350 PS 6-cylinder increased the power to weight ratio from 8.4 to 9.6 PS/t compared to the B1 Ter prototype (10.2 PS/t in the most favourable case for B1 Bis, 9.6 least favourable), the 400 PS V12 could possibly push that to 10.9 PS/t, possibly allowing greater top speed than the B1 Bis, closer to 30kph than 25.
Unfortunately, the protracted development of the B1 Ter meant that the fundamentals of the B1 (one-man turret with 47mm SA35, short 75mm hull gun, tall hull, relatively low speed and somewhat archaic suspension with multiple wheels and envelopping tracks) were unchanged. The B40, which we will discuss later, was to do something about that.
Prototype 101-based B1 Ter vs hull of the Rueil B1 Ter preproduction vehicle. The 75mm hull mount no longer blocked driver vision to the right, the front hull on the B1 Ter is more streamlined compared to the B1 Bis with its cylindrical spacer under the hull gun, the hole for the turret is now centrally mounted instead of being slightly smaller and offset to the left.
The story of the Char B40 as explained by military engineer LAVIROTTE:
Program
In 1940, the Committee to review battle tank projects decided :
- To replace the B1 Bis by the B1 Ter in future orders,
- To develop a vehicle derived from the B1 Ter with the following characteristics :
- Weight below 42 tonnes
- 80mm-thick front and side armor, 40mm-thick belly and roof
- Armament : 75mm SA 35 gun with horizontal traverse of the B1 Ter type, turret
This Committee, presided by Général Dufrenois, included :
- The tank inspector : Général Keller
- Representatives of the HQ (ARMET) : Colonel Armengaud, Lt-Colonel Marchand
Of the Infantry Direction : Commandant de Lescoet, Capitaine Le Gouest of the Engineers ;
Of the 12th Direction (Armament production) : General engineer Desmazieres, chief engineer Schneider, main engineer Lavirotte (ARL), military engineers Devenne, Molinié (AMX).
Realization of studies
Two projects were being prepared, launched by the design bureau of the 12th Direction, convinced that the G1 tank projects (Renault-FCM-BDR-SEAM) would not be accepted. One came from the ARL, the other from the AMX, the latter with a diesel engine and Alsthom electric transmission.
The ARL project intended to use the following components :
- Engine : Supercharged/Overcompressed Talbot V12 with a displacement of 19.9L– start of construction in May 1940 (author's note: evidence indicates that the engine was likely naturally aspirated). This engine could provide 500 PS at its maximum rating of 2500 rpm, and 450 PS at the normal rating of 2250 rpm. Cooling fans could take 50 PS. This engine was envisionned postwar to power the ARL 44 and various SPH.
- Cooling : B1 Ter type
- Fuel supply : B1 Ter type – fuel capacity : 1500L
- Transmission : gearbox studied by chief engineer Martin-Prével, mounted transversely, containing 6 forward speeds and 6 reverse speeds thanks to a reverser, a main differential, an auxiliary differential, both using spur gears driven by worm screws.
The brakes had been particularly well studied and derived from those equipping heavy trucks ; Bendix stop brake blocking the main differential and commanded by Bowden cable, two Bendix breaks with interior jaws mounted on the shafts of the auxiliary differential and commanded by Lockheed hydraulic system. Additionally these brakes could be used for steering.
- Steering : aside from the simplified and improved Naeder, two other devices of identical volume existed as prototypes
- the BN, electrical system studied by the SEAM led by Mr. Poniatowski
- the TAHV hydraulic system which was easier to produce than the Naeder ; it contained a generating pump with variable flow rate, a receptor pump, a distributor and accessories.
The TAHV was only bench tested at the supplier ; however the BN was mounted on a B1 Bis to test its principles ; it did not have the same advantages as the Naeder, in particular due to a certain delay in command and the fact the speed radios could vary from 90 to 70% depending on terrain. However, steering efforts were reduced, the Chobert radiator was deleted, maintenance requirements were nil.
The BN contained :
- A hexapolar generator
- An octopolar motor
- An excitator providing current to the generator and engine ; it could be excited by the battery if necessary,
- A regulator adapting the engine torque to resistive torque.
While the Naeder allowed immediate steering, the BN was delayed and it was impossible to anticipate the steering radius based on the steering wheel’s orientation ; the driver first had to bring the wheel to its maximum position to obtain engine speed, then bring the wheel back to the position desired for the radius.
Apparently, the simplified Naeder was selected over the alternatives.
Clutch :
Two models were intended :
- A Fieux clutch scaled for 450 PS coupled to a Ferodo cluth, via a Paulstra device.
- A Comète centrifugal clutch specially studied by the Ferodo company.
Running gear :
- Tracks : B1 Bis type widened from 500 to 600mm.
- Suspension : hydropneumatic type – each of the 3 groups of 3 stages of the B system (7200kg coil springs stroke 90.5 to 125mm, 20000 kg leaf springs stroke 125 to 155mm, rubber bump stops 27000kg stroke 155 to 160mm) was replaced by a hydropneumatic group studied by the DOP company. Each group contained :
- A cylinder with a filling tap,
- A piston moved by the roadwheel arm and supporting a second piston pierced with a hole, the
gap between them filled by oil
- A fixed diaphragm between the two pistons, also pierced with a hole.
An air mattress was compressed between the bottom of the cylinder and the 2nd piston ; this mattress, by changing volume, acted with smoothness on the roadwheel arm via the liquid which absorbed energy when going through the holes. Thus 600kg were saved compared to the B system. One of the 3 B1 Ter tanks tested it ; results were satisfying, but since it ran only 10 hours, it was not possible to make a clear assessment. The tank had to be withdrawn before the completion of the trials. It is unknown if the suspension would be suitable for the new weight of the tank.
A variant was proposed by removing the long roadwheel arms and replacing them with a hydraulic arm ; each small arm would have a piston compressing oil in a cylinder. The two cylinders were linked by a pipe which was itself linked in the middle to a hydropneumatic pump containing a cylinder, a fixed holed diaphragm, a mobile separator piston and a compartment to store compressed air. Even more weight would have been saved.
Return rollers :
3 forward and 1 rear return roller.
The axis of each leaf spring group was held by a piston cope/screed ( ?) compressing a rubber block in the cavity of the connecting rod.
Each group received two twinned semi-cantilever springs like the B1 Bis.
Arrangement of assemblies-independent boxes :
Each running gear bogie was housed in a box, the forward and rear boxes also containing the return rollers. These boxes were bolted to the hull and were easily removeable in case of bogie failure. Replacement of the bogies was easier than in B1 Bis or Ter. The boxes were stiffened by spacer plates.
Idler :
Hydropneumatic system : resistance of an air mass contained with sufficient pressure in a piston linked to a fork to which stresses were transmitted ; movement of the fork to regulate pressure was obtained by applying variable pressure on a differential piston with a filling pump.
The device contained :
- An oil tank
- A pump with a hand lever and venting command
- 2 cylinders (1 per idler) in which a differential piston linked to the small base of the fork was moving, and received oil pressure or compressed the oil on the large base.
A cavity in the piston was divided in two compartments by a diaphragm. The forward one stored compressed air and was filled by a pump, the rear one stored oil and communicated with the bottom of the cylinder through a hole, and with the lower part of the cylinder or the narrowest part of the piston through another hole,
- Piping to link the pumps to the cylinders,
- a leather gusset
The pump sucked up and drove back oil between the two cylinders, the loosest track being tensioned first until tension was equalized for the two tracks. Then the tracks were tensioned simultaneously until satisfactory tension indicated on the pressure gauge was obtained.
To loosen the tracks, one acted on the tap of the pump.
A device was mounted on one of the 3 B1 Ter tanks and proved satisfactory. Only a few pump shots were needed to tension the tracks.
Upper run of the tracks :
B1 Ter type – skids mounted on silentblocks
Lubrication :
B1 Ter type with centralized lubrication system.
Armor :
The sloped side armor plates of the B1 Ter were not retained considering the limited benefit provided by 25° regarding ballistic protection and complexity of arrangements.
80mm-thick front and sides, 40mm-thick belly, 30mm-thick roof, 40mm-thick running gear and sprocket protection, 60mm-thick rear.
The belly was organized to improve protection against mines and formed an assembly including the external side plates protecting the running gear, the belly itself, the 45° spacer plates between the belly and the interior running gear plates, and the two inverted Ls of the bogies (vertical 20mm, horizontal 20mm). The track covers contained a hinged part for cleaning and rail transport, the track cover extending slightly beyond maximum width. The intakes and exhaust were of the B1 Ter type with the same position. However the intake louvres at the rear were fitted with a spring equilibrator, the doors being unlocked from inside the vehicle.
Driver’s cabin :
Of the B1 Ter type with 70mm-thick plates, without changes.
Turret : ARL 2 with the turret ring diameter increased from 1218 to 1680mm (author’s note : 2 man crew with 47mm SA37/AC 34 with sliding breech. In reality ARL had turrets with other names with a similar configuration, so it is unlikely to be just an upscaled ARL 2).
According to historian Stéphane Ferrard, May 1940 fighting led to the project being revamped with a single 75mm gun with a muzzle velocity of 570 m/s (analogous to the 75mm M2 in the M3 Lee and Sherman prototypes/preseries) in a 3-man ARL turret with the hull gun being deleted. Allegedly a derivative of the ARL 4 which was studied for a fortification assault tank.
Layout :
The engine bay, thanks to the new layout of the gearbox, was now only 2.71m long instead of 3m on the
B1 Ter and 2.93m on B1 Bis (author’s note : Ter’s gearbox was 22cm shorter than Bis’, it is not certain what the actual engine bay length is on B1 Bis).
- Bulkhead
- B1 Ter type insulation on the exhaust piping,
- Exhaust pipes of the B1 Ter type
- B1 Ter type compressed air setup
Electrical installation : B1 Ter type
Rail transport : on a special 45 tonnes Sywf SNCF wagon. This implies that the B40 would likely have weighed no more than the 45 tonnes specified by the Keller program.
NOTA – Studies of the B40 continued during the Occupation in parallel to studies for a 30t tank for which the following components were considered :
- Continuation of trials of the supercharged 500hp Talbot with fine-tuning for ethanol use considering the situation
- Construction of a 500hp gearbox to mount and test it on a diesel BDR locomotive,
- Construction of a public works tractor to test the hydropneumatic suspension
- Development of a petrol-injected Brandt engine (Fabian system)
- Development of an Aster two-stroke diesel
- Development of a 500hp Cotal transmission
Moreover, stamped turrets and driver’s cabins were studied with small elements being clandestinely built by FAMH and Schneider.
A snow-plower and a trolley-bus with an electric transmission built in Nantes and transmission parts were also studied.
Overall, the B40 was a straightforward extrapolation of the B1 Ter to meet the Keller program's requirements. I have found no details on it so far in archives, so we are solely dependent on Lavirotte's postwar report. It would probably have ressembled the B1 Ter, but with a wider hull and tracks (likely 2.94m wide at the end of the tracks as this was the railway transport limit) and thus a squatter appearance. With the shorter engine bay and enlarged turret ring, the turret probably looked more centerline than on previous Char Bs. The turret would ressemble the ARL 2 and all other known ARL turret drawings (ARL 4 and 1 below).
The B40 also brought further improvements to mobility and quality of life, with the gross power to weight ratio at maximum engine rating reaching 11 PS/t, autonomy being definitely around 8-10 hours, and the transmission possessing an extra forward speed and now high speed reverse capability, a very rare feature in WW2/1940's tanks. Running gear replacement/maintenance was now easier, track tensioning as well. It is unlikely however that the hydropneumatic suspension, which was IRL tested on the ARL-44, would have been practical owing to sealing difficulties at the time (Tetrarch's airdraulic suspension had similar issues, as did hydropneumatic suspensions even in the 50s and 60s). Welding was generalized everywhere it is possible, which meant the tank's structure would have been even more mass-producible than the B1 Ter's.
The B40, which could have entered production in the Spring of 1942 at the latest, would have been a competitive heavy battle tank owing to its heavy antitank and antipersonnel capabilities, good armor, and actually very respectable mobility for a tank of its class, while at the same time not going too far in terms of weight, which could avoid the issues that plagued vehicles like the Tigers and KV-1.
Compared to the A22 Churchill which could have been its British counterpart in the Western front, the B40 was heavier and not necessarily more heavily armored (the front can be a little thinner in places), but enjoyed much greater mobility, would have had a somewhat larger turret ring, and possibly greater reliability and ease of maintenance as it could have capitalized on previous work on the B1 series, though it is certain that the A22's story would have differed quite a bit had France held.
However, the B40 would have retained some last drawbacks from its family: a likely tall hull, an inefficient running gear for high speed movement, and envelopping tracks which meant that the turret ring could not be as easily enlarged as a more conventional tank. In these regards, the B40 faced the exact same practical limitations as the Churchill tank, on top of having a taller and thus less weight-efficient hull (although this is offset by the lack of the frame the A22's plates were bolted on, and possibly a slightly shorter hull as the B40 did not need to achieve the trench crossing requirements from A22's spec).
The AMX Tracteur B was the other entry in the future battle tank program. The idea was pursued towards November 1939, as the automotive components of an AMX chassis developped for a 370mm SPH since 1937 were suitable for use on a tank.
The proposed characteristics were as such (in a letter from March 1940):
A) General characteristics
General dimensions: those of the B1 Ter (around 3.03m wide (including 500mm wide tracks), 7.098 m long in total (6.185m for the hull itself outside of the tracks), 0.925 m tall turret, 0.5m ground clearance, 1.415m tall hull without ground clearance, 2.84m tall)
Weight: 40 tonnes empty
Armament: a) 47mm APX casemate gun in a turret with no independent horizontal traverse relative to the turret (same performance or slightly higher velocity than 47mm SA37)
b) 105mm mle.1928 howitzer or 75mm gun from the B1 or 75mm APX L30 gun in the hull (the latter solution is the least interesting due to the weight and length of the weapon)
Possible horizontal traverse of a few degrees relative to the hull
c) machineguns (4 in principle: 1 coaxial, 1 in the hull front, 1 on either side of the hull (much like WW1 tanks to sweep trenches)
Crew: 4 men
1 commander who operates the 47mm gun and machinegun in the turret
1 driver - gunner for the casemate gun
1 loader of the casemate gun who also operates all the hull machineguns
1 radioman
Armor (all angles from vertical):
Front: 70mm at 32° upper, 80mm at the junction of upper and lower, thinning down at 60mm at 43° lower
Not sure if the plans show 2 different variants or just front/rear sides but if the latter:
Fronts sides: 70mm straight upper sides, 40mm at 60° above the suspension units (or 30mm at 79°), 70-60mm at upper straight parts of the suspension box, 70mm at main straight part of the box, 35mm box floor, 30mm thinning down to 20mm protecting the roadwheels
Rear sides: 60mm straight upper sides, 30mm at 60° above the suspension units (or 30mm at 79°), 60-50mm at upper straight parts of the suspension box, 60mm at main straight part of the box, 20mm box floor, 20mm thinning down to 15mm protecting the roadwheels
Rear: 55mm at 15° upper, 65mm at the junction, 40mm at high angles at the lowest point
Turret: 80mm for all three plates visible from the front at small angle, 70mm for all other plates at greater angles, 30mm roof, 70mm cupola
Roof and floor: 30mm (35mm for floor just under the driver, possibly 20 under the engine compartment)
Speed: 35-40 kph in a straight line
B) Particular technical characteristics
Running gear and suspension:
Solution derived from the AMX study for a 45t tank and the AMX study for the R35 and light tank.
B1-style track - metallic roadwheels mounted on silentblocs (already studied and tried successfully on the R35 at Satory) - twin teeth sprocket - elastically-mounted idler wheel
The suspension organs are protected by the hull.
Engine: Aster V12, 2-stroke diesel, 2200 rpm, 400 PS minimum (450 or even 500 expected in practice, especially based on the performance of the 4-cylinder engine). 1300 kg weight, 1200mm length and 900mm height specified. This engine drives an extra flat generator which allows the placement of the engine and electric transmission transverly to reduce the length of the tank.
Solution derived from the study already done by Aster for the 45t AMX project and the engine in development for the light tank. It would share the same cylinder, the same piston and liners...
The engine would be set transversely.
II Special organs
Carcass: in principle it would use a construction with cast and rolled elements. Bending the rolled plates in a single plate would be used to the maximum extent. All shaped pieces (louvres, mantlets, etc) would be cast. The carcass forms the chassis.
Turret: hydraulic traverse (like HELE SHAW SAT) allowing aiming of the 47mm gun using the turret (coaxial MG on the right of the gun). Octagonal cast turret reminiscent of the APX-R of the R35 and Hotchkiss light tanks, rotating cupola like the APX-1/4 of the B1. Sits on a 1285mm roof opening (1130mm for light tanks, less than 1285 for APX 4), 1170mm turret ring width at the ball bearings (1022/1070 for APX 4), 1035mm free internal turret ring diameter. 4 tonnes fully loaded without ammunition.
+15°/-10° elevation angles.
Equipped with 1 episcope on either side of the turret, 1 on the front left side plate, 1 vision slit on the rear door.
c) Weight distribution:
Carcass: 16.500 kg
Empty turret: 3.500 kg
Suspension: 10.500 kg
Engine: 1.300 kg
Transmission: 4.000 kg
Radiators and fans: 700 kg
Fuel tanks: 200 kg
Hull gun: 1.000 kg (maximum)
47mm gun: 800 kg
Gun masks: 300 kg
Misc: 1.200 kg
Empty weight: 40 tonnes
Ammunition: 1.500 kg
Diesel fuel: 500 kg (around 600L)
Water: 200 kg
Crew: 400 kg Total: 2600 kg
The weight distribution has been largely calculated to not exceed 40 tonnes empty. As such, a margin has been allowed for unknowns.
Regarding the hull gun, we have used the weight of the heaviest gun (the 75mm APX). It seems acceptable to anticipate rail transport of the tank without ammunition and with a very reduced quantity of ingredients (fuel/water).
E) Required credit
The studies of the engine, transmission and running gear being already done for the ATS 370mm SPH, the study costs of the prototype would be severely reduced. Normally a prototype of this importance with mild steel carcass and turret would cost 6 million francs. At the minimum a 3-million-franc credit (2 in 1940, 1 in 1941) should suffice.
Timeline: The maximum time to gather all the organs is estimated at approximately 14 months from the agreement on the project. 3 months would be needed for assembly. The tank could roll out in July 1941.
In the case the proposed study was deemed interesting, it would be relevant to:
a) specify the gun to use for the hull mount (I prefer the 105mm howitzer).
b) obtain support from an artillery design bureau for the installation of the specified gun (if possible APX or the Havre construction workshop, who already know armored vehicles).
c) obtain support from the APX for the installation of the 47mm gun in the turret.
d) Provide the dimensional plans of the weapons to the AMX
Signed: Molinié (lead engineer at the AMX)
The AMX project featured a very big hull, even moreso than the B1 Ter itself, so it shared the same issues of weight inefficiency. Much like the AMX 38, AMX didn't try to meet the full requirements of the Keller program in terms of armor protection (although still very respectable) and turret layout (only 1-man instead of 2-man at least). In fact it would have been a huge achievement if the long 47mm ammunition could be loaded well enough in that turret which was bigger than the APX-4, but only by around 100mm. That and the fact it didn't capitalize on the B1 manufacturing complex like the B40 meant that it would probably been at a severe disadvantage, unless it was massively reworked to install a proper 2-man turret.
The most interesting part of the tank was the powerplant. The transverse layout of the engine AND generator was quite an efficient move. The engine itself was in many regards a direct French analogue to the postwar Detroit Diesel 12V-71, considerably more compact than the twin 6-71 engine setup of WW2 (and saves 700kg), with the potential for more power than the twin-71. This was probably the all-around most promising French tank engine in 1940, unless the small size of the Aster company makes it unable to compete with Talbot and its gasoline V12 (the second most promising). The diesel engine also meant the Tracteur B needed far less fuel than the B40 to meet range requirements (though the B40 probably has greater autonomy here, because it carries 2.5 times the fuel quantity).
The title "Ultimate Off-Roader" shouldn't be awarded without consideration of this 1939-40 prototype French recovery vehicle, the Latil M4TX3:
This little baby had enough drawbar force to tow a B tank with locked treads on soft or hard ground, or pull a 155mm gun out of mud to the tire tops. It also had a very powerful winch and anchor spade, for even heavier jobs. Regrettably, the French ran out of time to get it into production.
No, the program didn't deal with support vehicles. The Latil was apparently developped for a 1938-39 program calling for a recovery vehicle for Char B and Somua units, with the M4TX being the preferred vehicle rather than the Laffly S45T which was deemed insufficient and the Somua MCL 6. Down the line the M4TX would have equipped all Char B battalions and would still apply for B1 Ter and B40.
I just found in a report why the program didn't include replacements for the Somua and Hotchkiss H39 (for fast tank roles). The reason was that it was decided that production of these types would continue until needs were met.
Keller himself reviewed his 1939-40 program in a document from February 1941 following lessons from the battle of France and while this was written partially in the context of France having less ressources than before the Armistice, he did include some ideas regarding the tanks of the program (though the bulk of his writings are really about doctrine and organization)
- for the future fortification assault tank, focus on studying the automotive parts as they will be the determining factor for the rest of the design.
- for the battle tank, no particular changes other than recommending diesel engines to reduce fuel volume and weight and generally even greater emphasis on improving the power to weight ratio of the vehicle, as the components of the B1 Bis could be massively improved on.
- for the infantry support tank, recommend using basically half of the engine of the battle tank for commonality and setting up the gear ratios so that a maximum speed of 40 kph can be achieved to replace the Hotchkiss H39 down the line and generally be more versatile.
- Plus more general statements on the design of turrets (even greater emphasis on 2- and 3-man types, redesign of the gun mounts for reduced height and more space) and need for ease of maintenance and durability.
I've seen it said on Tank Encyclopedia that it was proposed to modify the Char B40 by installing the 75mm gun-armed turret from the ARL Char de Fortresse in response to combat experience during the German invasion. Did you find anything mentioning that?
I've seen it said on Tank Encyclopedia that it was proposed to modify the Char B40 by installing the 75mm gun-armed turret from the ARL Char de Fortresse in response to combat experience during the German invasion. Did you find anything mentioning that?
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