ARL V 39 French self-propelled gun

[Elan Vital]

Hi everyone,

New topic based largely on my research in the French archives, this time on one of the more elusive prototypes of late 30's France: the ARL self-propelled gun, also sometimes called the ARL V 39.

Preliminary history:

The story of French self-propelled 75mm guns date back at least all the way to the early 1930s. Such a concept is envisionned during a meeting of the Consultative Council on Armaments in July 1932, to cover French tank attacks against other enemy tanks, following experiments of combined arms exercises. The need to complete this study is reiterated in January 1933, and once again in March 1934.

"In early 1935, a first testbed built by the APX arsenal under the auspices of General GARNIER is presented to the Council.

This materiel was built on the basis of the D3 colonial tank (a lightened derivative of the Char D2 prototype), specially modified to mount a 75mm mle.1929 casemate gun (used on the Maginot Line), modified with a semi-automatic breech. It was trialled at MAILLY in May 1935. The experiment is unsatisfactory.
Aiming using the tracks is difficult and delays the opening of fire; aiming and maneuver incidents are common, owing to the high overhang of the gun in front of the vehicle. Crossing capabilities are insufficient.
Overall, this prototype is deemed insufficiently maneuverable, protected and safe to fire. As a result, the study of new vehicles benefitting from the lessons of this experiment are started:
- one by Renault with assistance from General GARNIER
- the other, by the APX.

The two projects are as follows:

	GARNIER-Renault project	APX project
Weight	20 tonnes	21 tonnes
Armor	35 to 45mm	30 to 50mm
Engine	Gasoline 180 PS	Diesel 260 PS
Crew	4 men	5 men
Armament	1 75mm gun	1 75mm gun, 1 turreted 7.5mm machinegun
Vertical traverse arc	-10 to +30°	-10 to +30°
Horizontal traverse arc	12° (6 either side)	12° (6 either side)
Capacity	160 rounds	200 rounds, 1500 machinegun cartridges
Maximum instantaneous speed on roads	25 kph	36 kph
Range	150 km	400 km on roads (14 hours autonomy)
Crossing capability	No data (the 1st prototype was insufficient in this regard)	Over 1.8m
Protection against gases	Seems doable.	Seems doable.
Radio	None	One radio
Observation	Rangefinder	Rangefinder, one binocular periscope, one rangefinding monocular periscope

Consulted on the opportunity of starting work on the prototypes, the 3rd Direction, the 12th Direction and the General Inspector of the Artillery agree to start work on the PUTEAUX prototype with a few detail changes, due to the particularly interesting features it includes (diesel engine, radio, close defence machinegun, etc...) and due to its design itself which accounts for the last progresses made in tank design.

The opinions have been less affirmative regarding the GARNIER-Renault project, which mostly benefits from the trials of the first protype, the defects of which it aims to fix. Perhaps could it then be more quickly done.
Moreover, it is worth noting that the cost of a 75mm SPG is 2-3 million francs. It is currently impossible to envision the simultaneous order of both prototypes, and it is likely to be the same in 1936 as well, due to the importance of other undergoing or planned studies for artillery equipment and many new ammunition."

Source: Note on 75mm SPGs in GR 7 N 4209

ARL V 39 is next.

 

[Archibald]

Canon de 75 modèle 1897 - Wikipedia

en.wikipedia.org

Wikipedia says 21 000 "canons de 75" were manufactured. No surprise it lasted so long, the stock was of Soviet artillery depot size...

 

[Elan Vital]

Canon de 75 modèle 1897 - Wikipedia

en.wikipedia.org

Wikipedia says 21 000 "canons de 75" were manufactured. No surprise it lasted so long, the stock was of Soviet artillery depot size...

Around 5320 as of May 10 1940, a very respectable number backed up by a production capacity of at least 175/month to grow to 300/month by August (these were production figures dating from June 1940 assuming a defense on the Loire river, so possibly conservative!).

For the gun used on the ARL V 39 (and planned 75mm tank turrets), existing stocks of guns couldn't be used but ammo could.

 

[Archibald]

Wait, there were still producing these guns ? I thought production had been discontinued sometime during the Interbellum.

 

[Elan Vital]

Wait, there were still producing these guns ? I thought production had been discontinued sometime during the Interbellum.

It's not clear if we were producing them before May, only parts it seems. However they are referenced in a study made on the 15th of June in case the French held on the Loire river:




Might have been some emergency production to replace the exceptionnal losses.

The rest for what it matters:

 

[Scott Kenny]

Even if they were just producing "parts", you do end up needing lots of gun barrels if there's a lot of training, because barrels are a wear item. And in that training, I'm sure some carriages will get broken.

So I'm sure that you could count a small production of "guns" among all the parts, just because you did make all the different parts. You just didn't necessarily assemble them into complete guns.

 

[dan_inbox]

the ARL self-propelled gun, also sometimes called the ARL V 39.

Here is a photo of the Canon automoteur ARL V39, aka ARL 1940 V939:

 

[Elan Vital]

History of the ARL V 39/ ARL 40:

Not much is known still, little more than Wikipedia had to say from the existing sources. What is known is that the APX project from 1935 eventually got taken over by the ARL when this branch of the APX got renamed. In June 1938, a mild-steel prototype was finally completed and was tested in March 1939, passing tests. Part of the delay was caused by the long development time of the 75mm gun.
It ended up competing against the Somua SAu40, as the Cavalry had also arrived at the concept of 75mm SPG to assist armored units. The more convenient fighting compartment of the ARL won out.

The ARL V 39 was meant to equip the 4 planned DCR armored divisions of the Infantry, with 12 SPGs per division spread out over two battalions of 6 made up of two batteries of 3, so 48 armed SPGs. An additional 24 unarmed command variants were ordered, for a total of 72 ARL V 39s.
In April-May 1940, it was decided that the 36 Somua SAu40 ordered for the cavalry would be rearmed with the 47mm mle.1937 after it had been realized that the 47's antitank projectile had excellent concrete dislocation effects. As a result, the ARL V 39 was expanded to 108, 36 thus being presumably intended for the Cavalry's DLM armored divisions. 5 were to be delivered in August or October 1940, followed by 10/month thereafter.
It can be assumed that if a successful France had got to the stage of building additional DCR and DLM divisions ( 5 DCR including one Polish, 3.5/4.5 DLMs including 0.5 Polish), the ARL V 39 order would have been expanded by 12 (+6 command) vehicles per additional division.

This never occured, with apparently 2 prototypes being completed by May-June 1940 and the rest of the serial production program being 20% complete before France fell. The prototypes would be lost during the war after having been evacuated to North Africa.

What can be noted from this small order is the niche role of the ARL V 39. Unlike other casemated SPGs like the StuG III or the SU-85, the ARL was not meant to be a cheap tank destroyer or supplement to normal tank production. This is reflected in its actual design, which was surprisingly sophisticated for a vehicle of this type. Nonetheless, it is possible that its role would have been considerably expanded as its true value gets recognized. In particular, its powerful 75mm gun backed up by an impressive fire control equipment represented a uniquely powerful mobile antitank capability for the French tank formations of 1940-1941, especially as no firepower improvement beyond the 47mm SA35 was expected for French turreted tanks until 1942 or maybe late 1941 (per pre-May plans of course).

Onto the design later on.

 

[Archibald]

Impressive machine.

 

[Elan Vital]

Design of ARL V 39:

The design corresponds from the description of the provisionnal manual from January 1939 (seen at the top of Part 2 of my archive photo albums). In spite of its somewhat conservative if not archaic appearance and the assumed simplicity of WW2 casemated SPGs, the ARL V 39 was actually one of the more sophisticated French AFVs meant to enter production in 1940.

Crew organisation:

The crew was composed of:
- a crew commander/observer
- a driver/gunner
- a radio/2nd gunner
- a loader
- an "artificier"

The commander had his own cupola, reminiscent of the APX-R light tank turret. This observation turret was equipped with a PPL vision block, a binocular periscopic x8 sight, and a stereoscopic rangefinder. A 7.5mm machinegun was fitted for close self-defence, but the ARL was meant to operate somewhat behind the main attacking force.

On top of his normal command and observation duties, the commander thus could range enemy targets and automatically transmit the gunnery data in azimuth and elevation directly to the gunners. France was apparently the very first country to seriously aim to implement optical rangefinders in AFVs, which could allow more accurate long-range fire at the cost of a longer aiming procedure and new crew selection requirements.

The driver had his own sight and could orient the gun in elevation (-10/+30°) and traverse (6° either side, then move the entire vehicle). This was an unusual setup, but arguably makes sense considering the tank has to stop to fire and needs to turn when the target is beyond the small 12° horizontal traverse arc. Only he could fire as he was the sole person in control of the azimuth.

The radio had an ER26 Ter/ R61 emitter-transmitter, and had his own sight and controls for orienting the gun in elevation only, to assist the driver.

The ARL could use indirect, semi-direct (cupola out only) and direct firing modes.

To use the full fire rate of the gun, the work was spread between a loader and artificier. The latter extracted ammunition from the side ammo racks to replenish two 8-round bins and set up the fuzes. The bins could be set up so that the loader could load the gun very quickly without changing positions.

Protection:

The ARL V 39 didn't follow the armoring rules of normal French tanks. The frontal and rear plates were cast and bolted to the side sponsons (which sat between the upper and lower runs of the envelopping tracks, just like B1 and Churchill tanks), while the rest was rolled and welded.
The front plate thickness went from 50mm at 0° to 40mm at 60° from the vertical, with the gun mask being 50mm thick at 35°.
The sides plates were 30mm and vertical, the rear was 40mm thick and vertical.
The roof was 15mm thick and the floor 10mm thick, and was thus not safe against AT mines.
The turret itself was armored at 40mm all-around with the walls angled at 30°.

Overall, the ARL V 39 was quite well-protected for its time, but the armor distribution wasn't as favorable as that of normal French tanks.

Engine:

The ARL V 39 was fitted with the Hispano-Suiza V12 engine used on the J12 luxury car and originally intended for railcars. This engine had already been selected for another vehicle, the SEAM G1P battle tank, the development effort of which had been headed by Prince Poniatowski, a major investor in Hispano-Suiza.

This engine had been designed according to aircraft engine practice, and as a result was remarkably power-dense for a French AFV engine of the time.
With a compression ratio of 6 (truck fuel) and a displacement of 11.31 L (100mm bore and 120mm stroke), it provided 250 PS at 2800 rpm and 240 PS at 2400 rpm. For the 25 tonnes of the vehicle, the power to weight ratio was the minimum 10 PS/t required by the Army. Nonetheless, this was apparently still too low as a further optimized tank variant of the Hispano engine was intended for serial ARL V 39s, delivering 300 PS (340 PS was also mentionned as a target for the SPG).

The engine was mounted transverly in the ARL, which reduced the length of the engine compartment and saved room for the fighting compartment. This was an extremely rare layout in WW2.

There was 450 L of fuel in two 225 L tanks, which should have been sufficient for at least 8 hours of autonomy.

Transmission:

The ARL used a fairly advanced transmission, built around the Cotal preselector system, analogous to the Wilson system but using electromagnetic clutches.

With a total of 8 forward speeds and one reverse speeds, it could reach a maximum instantaneous speed of 42.3 kph at 2800 rpm (36.3kph at 2400 rpm), and a reverse speed of 5 kph. In reality, the actual speed would be somewhat lower, but this was respectable considering the power to weight ratio.

The tank had two steering radii per gear, for a whopping 16. There was an additional auxiliary steering method for a very small radius. Finally, a reverser was there to outright reverse a track when the other was moving forward, allowing the ARL to turn in place.
Overall, the ARL was likely to be one of the easier WW2 tanks to drive owing to the sheer flexibility of the system and the assistance devices.

Suspension:

As usual, the ARL used a running gear composed of small but numerous wheels to improve load distribution. The pitch was rather short however at 90mm.
Each side had 8 double wheels distributed in 4 bogies with 2-wheels per bogie, with two return rollers (one front, one rear). The spring element was made out of rubber blocks.

Main armament:
The main armament was the 75mm APX gun for self-propelled vehicles, designed not only for this vehicle, but also the ARL 3 tank turret and the unbuilt 45t fortification assault tanks from 1937. This gun had been built based on the 30-caliber mle.1929 casemate gun from the Maginot line, which had a very thick and thus somewhat heavier barrel than usual for tank gun. But it provided protection for the barrel itself.
The gun had quite rare features for WW2, with an automatic breech (it closes and opens automatically), and what was called an "automatic loader", which was in reality a spring-based rammer. The spring was retensioned by the return to battery of the gun. This reduced the task of the human loader to simply putting the round on the loading tray and pulling a lever to release the spring, which would ram the round inside.

Otherwise, the gun was just as powerful as the mle.1897, firing an AP projectile at 570 m/s (here the naval mle.1910 M APHE round, pending its replacement with modern capped APHE and maybe HEAT and APDS), and a HE round at 400 m/s. Maximum recoil was normally 375mm. The mle.1910 M round could penetrate 50mm of RHA at 0° at 1000m, 65mm at 500m.

The gun had a overhang of 400mm in front of the hull. It was possible to retract the gun 400mm inside the hull to prevent it from sticking into something during off-road movement.

Nearly 200 rounds could be stowed, with the two 8-round ready bins and two 94-round racks, one per side sponson.​

Dimensions:

Length: 5.8m in total
Width: 2.57 in total, 2.37m at the tracks
Ground clearance: 0.4m
Height: 2.45m
Track width: 400mm.

Conclusion:

The ARL V 39 promised a vehicle largely built around its primary armament. The compact engine bay and side sponsons allowed a very roomy fighting compartment with a lavish supply of ammunition. The stereoscopic rangefinder increased the practical firing range of the gun, while the rammer, automatic breech and shared workload between two humans for ammunition handling allowed a high rate of fire.
The gun itself, though quickly surpassed in WW2, was a very potent asset in 1940-41, comparable to the American 75mm M2.

In terms of mobility and protection, the ARL held somewhat of a middle ground between the infantry and cavalry tanks, but with no AT mine protection, which was acceptable given its role. If the more powerful engines were employed as intended, it would however have been one of the most mobile French AFVs of the period.

In many ways however, it was not really comparable to other tank destroyers and assault guns of WW2, being intended as a less common but relatively advanced asset.

By 1940 however, the long term future of the casemated SPGs was being questionned. The growth of the G1 battle tank program into turreted 75mm tanks led to some ideas in the military to possibly supersede the casemated SPGs with more flexible turreted models. The result of the G1 program, the Renault design, was not contemplated as the future battle tank due to it not meeting the specifications, but the 75mm turret it mounted attracted significant interest. The ARL V 39 may well have been superseded in late 1941 with a new vehicle.​

 

[Archibald]

That kind of project is proof that, as far as strategy, design and prototypes were concerned, 1940 France was moving in the right direction. What didn't moved the right way AT ALL was a) the Army HQ b) politics and c) the industrial base, by large. There were deadly bottlenecks there.

 

[Elan Vital]

That kind of project is proof that, as far as strategy, design and prototypes were concerned, 1940 France was moving in the right direction. What didn't moved the right way AT ALL was a) the Army HQ b) politics and c) the industrial base, by large. There were deadly bottlenecks there.

Speaking of the industrial base, I forgot to mention that the task of building the V 39 was given to the Baudet-Donon-Roussel company (the same BDR as the G1B), contributing further to the expansion of the French wartime industrial base.

I'd say that the turning point for French tank technological development was 1937, even if it didn't lead to production vehicles yet by mid 1940. There was a major effort towards optical rangefinder and loading assistance methods, plus progressive engines and suspensions, to a degree that was rather exceptionnal in the West. A very similar spirit to the postwar USSR.

 

[Elan Vital]

New interesting update following the findings of document GR 9 NN 12 64 at the Châtellerault archives regarding French tank engine studies: on March 23rd 1939, the Defense and War Ministry had asked the ARL design bureau to study the replacement of the Hispano engine in the ARL V 39. Following exchanges with the AMX, the ARL drew up a specification for a 340 PS engine to fill this task, as well as a more general specification for suitable armored vehicle engines. These specifications aimed to obtain greater power in the same or a smaller volume, while keeping range the same by reducing specific fuel consumption.

The ARL consulted many manufacturers. The one most related to this plan is the Edgar Brandt Establishments, which had been making the Hispano Type 68 Bis engine powering the ARL V 39. Brandt had tested a direct fuel injection system in one of their truck engines, and following promising trials, ARL tasked them with drawing up a project for a 340 PS class engine in early 1940.

The result was a V12 fuel-injected gasoline engine with a bore of 110mm and a stroke of 125mm, so a displacement of 14.3 liters (as opposed to 100, 125 and 11.3 respectively for the Hispano Type 68 Bis). Max continuous output was 300 PS at 2400 rpm (instead of 240) and peak output for 30-minute-running was 340 PS at 2800 rpm (instead of 250). Output for road marches was 240 PS at 2800 rpm.

Thanks to the fuel injection, specific fuel consumption was reduced to 220 g/PS/hr instead of the minimum 248 g/PS/hr of the Type 68 Bis, and the fuel consumption curve was flatter. Moreover, the engine was to be compatible with 60-65 octane Army gasoline rather than the slightly higher octane heavy truck gasoline with 15% alcohol additive used in peacetime.

The dimensions (L * W * H) were 1160 mm, 700 mm and 850 mm respectively, to match the volume of the Hispano Type 81 Ter that this engine was contemplated to replace (unknown engine, this might have been Hispano-Suiza's name for a 300 PS engine to replace the 68 Bis).​

Delivery intended in early 1941 for the prototypes. The development of the Brandt fuel-injected engine continued in secret after the Armistice, but its fate remains unknown.

Another engine developped for the 340 PS class, but possibly not for the ARL V 39 was the Talbot V400, a carburetted V12 with a bore of 120mm and stroke of 130mm (displacement 17.65 liters) and a CR of 6. This would have provided the same performance as the Brandt engine but with a specific fuel consumption of 240 g/hp/hr at 2800 rpm.

However, it could be retuned to provide 325 hp at 2400 rpm continuously and 380 hp at 2800 rpm for 30 minutes, with a specific fuel consumption under 270 g/hp/hr, thus trading fuel consumption for the possibility to provide increased power for possibly heavier vehicles. Delivery of 3 prototypes intended between July and September 1940.