Throughout most of the interwar years, the workhorse of the French army remained the Renault FT light tank. Developed under the direction of Louis Renault and with the support of General Estienne during the First World War, the small, manoeuvrable, and cheap to produce light tank proved very effective in comparison to the larger and sluggish Saint-Chamond and Schneider tanks. By the 1930s though, the FT’s heydays were gone, and innovations in tank design meant the vehicle was rapidly becoming massively obsolete. Though some efforts had been undertaken to update and produce heavier tanks derived from the FT during the 1920s and early 1930s, resulting in the Renault NC and then D1, those were not adopted in massive numbers, with just 160 D1s built for the French military.
The 1933 light tank specifications
Anticipating a replacement for the FT would soon be requested by the French military, Hotchkiss offered, in June of 1933, their preliminary design – by that point a turretless, machine-gun-armed project. Hotchkiss’s proposal ended up as somewhat of a self-fulfilling prophecy, pushing the French army to establish requirements for a new light infantry tank to replace the FT.
Those new requirements were finalized on the 2nd of August 1933. Though their formulation was a result of Hotchkiss’s proposal, they would be sent far and wide across French industrialists, with up to 14 different manufacturers working on a design; indeed, the role of replacement of the FT, the French Army’s workhorse, would logically lead to massive contracts, as this was no irrelevant vehicle to replace.
The specifications sent to the various manufacturers were quite detailed, with performance requirements in a number of different aspects. The tank was to weigh 6 tonnes, feature a crew of two, and be armed with either one or two 7.5 mm machine-guns, or a 37 mm gun. The maximum speed should be of 15 to 20 km/h, the armor 30 mm thick, and the vehicle should be able to run for 8 hours and at least 40 km. A large number of mobility requirements were also made, such as being able to climb a 65% slope, be stable laterally on a 60% side grade, and to cross a 1.70 m wide-trench or ford water 1.20 m deep, among others. Generally, the requirements called for a vehicle very similar to the FT in role and capacities – merely updated to take into account some more modern features.
The state workshop of APX
One of the five manufacturers which went as far as manufacturing a prototype was the Atelier de Construction de Puteaux (ENG: Puteaux Construction Workshop), abbreviated as APX and sometimes known simply as ‘Puteaux’, after the commune they were installed in within Paris’ suburbs. Founded all the way back in 1866, this state-owned workshop mostly worked with artillery and firearms, producing the designs of various engineers and sometimes designing their own. They were not one of the first French manufacturers to get into tank production, though the SA 18 37 mm gun found on the FT was a Puteaux design. During the 1930s, Puteaux would extend their operations into the field of armored vehicles quite considerably; the majority of turrets mounted on French 1930s armored vehicles, from the Panhard 178 to the B1 Bis’, were designed by Puteaux. That being said, their proposal for the 1933 light tank program appears to have been the first tank designed by APX from the ground up.
The APX proposal
APX presented the project for their light infantry tank in February of 1934, and the vehicle’s design is mostly known from the plans that were presented then.
The tank designed by APX was a vehicle quite diminutive in size, with a length of 4.40 m, a width of 1.58 m, and a height of 1.85 m, turret included. As for the ground clearance, it was quite low, at 0.35 m.
The vehicle used cast construction for both the hull and turret. Though the vehicle was small in size, the hull was, in comparison to the other light tanks submitted by other manufacturers, quite bulky. The driver’s compartment is easy to point out, sticking out from the front, and not being angled in the part featuring the vision port – something quite uncommon for cast French tanks. The angled part below featured a large two-piece hatch from which the driver would enter the driving position, which was noticeably low. The armor of the vehicle was 30 mm-thick all-around.
Powerplant and suspension
A somewhat notable feature of APX’s tank was the use of a diesel engine, a feature it shared with FCM’s proposal, which would become the FCM 36. In the case of the APX tank, the engine used was a two-stroke, 4-cylinder engine producing 65 hp at 2,500 rpm. With the weight of the vehicle being 6.85 tonnes, the horsepower-to-weight ratio was 9.5 hp/ton, a decent performance for an infantry support tank; the speed, with 19.8 km/h, was within the expected performances. The engine consumed 7 liters of fuel hourly on average, giving the vehicle a range of 150 km, or about 10 hours, thanks to its 70 liters fuel tanks.
The transmission was installed at the rear, as was the radiator, installed in the sloped, rear part of the engine compartment. The mounting of the transmission led to the drive sprocket being at the rear of the vehicle, and the idler wheel at the front. The suspension consisted of 5 bogies with two road wheels each, the front bogie facing the front and the four others the rear, as well as an independent wheel between the rearmost bogie and the drive sprocket. There were four return rollers at the top. The suspension would, in operation, be covered by a side skirt, which featured openable covers in order to oil and maintain the road wheels. The rear drive sprocket was not covered by this side skirt.
Turret and armament
The APX light tank’s turret is a quite notable one in the history of French turret developments. By December 1933, APX had launched itself into the design of cast turrets, first for the B1 heavy tank, but soon for its own light tank.
The result was a mostly cylindrical turret design, featuring a rounded observation cupola on top, a door at the rear, and a mantlet sticking out at the front. Two vision ports were present, one on each side. The turret was notable for mounting both a 37 mm SA 18 main gun and a 7.5 mm machine-gun – while the program originally requested a vehicle that would have either, but not both. It should be noted the exact model of the 7.5 mm machine-gun which was to be used is not known. While the 7.5 mm MAC31E, which would become the standard French tank machine-gun of the 1930s, appears as the most likely answer, the FM 24/29 light machine-gun has occasionally been mentioned as the vehicle’s secondary armament. It should also be noted that another version of the APX tank, featuring two 7.5 mm machine-guns instead, may have been considered.
The turret was crewed by the commander, who also assumed the roles of gunner and loader. He sat on a retractable seat that rotated along with the turret, though reaching down quite far in the hull’s fighting compartment below. Ammunition for the 37 mm gun was stored on the sides of this combat compartment; the quantity of shells carried is not known.
An elusive prototype, suffering from anti-state bias
It appears that a prototype of the APX light tank was manufactured, being completed in October of 1935. Very little is known about it, and no photographs have survived to this day; it is known the prototype was still in existence by 1938, with a mention of a new oil pump being in construction for the design in a document dated from the 15th of December 1938.
Despite a prototype being manufactured, the APX light tank does not appear to really have been taken into consideration for adoption. APX was the only state-owned manufacturer to go as far as manufacturing a prototype, and this state-owned status appears to have warranted the prototype an ‘out of competition’ status.
It should be noted that the requirements for light infantry tanks were edited in May of 1934, now requesting a 40 mm-thick armor while raising the maximum required weight from 6 to 8 tonnes. It is not known if this change in requirements was considered when manufacturing the prototype.
The influential APX-R turret
While APX’s light tank design as a whole is obscure, its turret is not. It was, in 1935, adopted on both Renault and Hotchkiss’s light tanks, under a version that appears to have undertaken some minor evolutions, but remained vastly similar. This turret would be known under the designation of APX-R; featured on both the Hotchkiss and the Renault light tanks, which would become the two most produced French tanks of the 1930s, it would by far be the most common turret design in the whole of the French military by 1940, and even be refitted with a longer 37 mm SA 38 gun from 1939 onward. This massive borrowing from the APX light tank remains its main legacy, though one could hardly argue for it to be a particularly great one; the APX-R’s one-man design resulted in the commander being utterly overtasked, and even for a one-man turret, it was quite horrendous and inefficient ergonomically.
Conclusion – An APX venture of questionable success
The APX light tank is, in itself, a quite obscure vehicle. An unlucky competitor to the R35, H35 and FCM36, despite seemingly reaching the prototype stage, no photos have been known to survive up to this day. The light tank does not appear to have been seriously considered for the role of standard light infantry tank for the French army either.
Nonetheless, the influence of the design via the APX-R turret ought not to be underestimated – thousands of French tank commanders would, in the later interwar and during the campaign of France, serve in a turret design originally designed for the APX 6-tonnes. As for the prototype itself, its eventual fate is unknown. As often with French pre-1940 French prototypes, the most probable fate of the vehicle was scrapping, though the question remains, by whom; The French prior to 1940, the Germans during the occupations of France, or even the French during the post-war reconstruction era? It appears unlikely an answer to this question will arise anytime soon.
APX Light infantry tank specifications
|Dimensions (L-W-H)||4.40 x 1.58 x 1.85 m|
|Engine||2-strokes 4-cylinders diesel engine producing 65 hp at 2,500 rpm|
|Maximum Speed||19.8 km/h|
|Power-to-weight ratio (in hp/ton)||9.5|
|Fuel tanks capacity||70 lites|
|Average hourly fuel consumption||7 litres|
|Range||150 km/ 10 hours|
|Crew||2 (Commander/gunner/loader, Driver)|
|Armament||1 37 mm SA 18 main gun, 1 7.5 mm machine-gun (either MAC31E or FM 24/29)|
Tous les blindés de l’Armée Française 1914-1940, François Vauvillier, Histoire & Collection editions, p48
Trackstory N°4: R35/R40, Editions du Barbotin