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
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