Saturday 10 August 2019

Rejected by Infantry, Adopted by Cavalry

France entered WWII armed with three different types of modern light tanks. Two of them were the numerous Renault R 35 and rarer FCM 36, used by only two tank battalions. The third tank, and a very numerous one, was the Hotchkiss H 35 (and its improved variant, the H 39). Overall, the H 39 turned out to be the best French light tank. It turned out to be very reliable and more mobile than its cousins.

Casting towards the future

The early 1930s were a time of experiments for tank builders worldwide. France was no exception. The French army couldn't settle on what they wanted in the 20s, and the tank industry proposed rather unusual vehicles. As a result, the French army received just one new tank by the start of the 30s: the Renault D1. The tank was an off one. At a mass of 14 tons it was still considered a light tan, even though some medium tanks at the time were lighter. The tank was not produced in large numbers. Its descendant was the Renault D2, not a light tank anymore, but a medium one. The French made their tank too large and expensive while chasing improved characteristics.

The first prototype of a Hotchkiss light tank, January 1935.

At the time, tanks were typically assembled using frames and rivets. Welding of armour was only starting to take off. The pioneers here were Germans, with their welded hulls for Grosstraktor and Leichttraktor tanks. Of course, nobody except German and Soviet specialists knew this, since the tanks were built illegally.

Another method of building tank hulls and turrets was casting. The Renault FT was the first tank were cast parts were used. Casting allowed production of large and complex components without extra joints. However, nothing larger than a turret or elements of the hull was cast until the early 30s. Tanks had bulletproof armour around 15 mm thick and there was no sense in making it cast.

The same vehicle on a truck bed.

In the 1920s Renault had no competitors in the field of tank building. Attempts by FAMH to produce 3 ton tankettes ended poorly. The situation changed in the 30s when the Hotchkiss company started to try its luck. Until then the arms giant had not tried to produce tanks, only armoured cars.

Hotchkiss got into tanks thanks to Henry Mann Ainsworth, the company's general director. Formerly a British officer and a fan of automobiles, Ainsworth kept a close eye on the global tank industry. He was keenly aware of issues faced by French tank building. That is when Ainsworth had an idea of building a 5-6 ton tank that could replace the ageing Renault FT. Ainsworth proposed that in order to save mass, these tanks should not have a turret and have a layout similar to the British Carden-Loyd tankette. The driver and commander, who doubled as the gunner, sat shoulder to shoulder. Unlike the Renault FT and its descendants, the transmission was moved to the front. This decision was copied from the British tankette and allowed the hull to be shorter.

The two experimental vehicles had a hump above the engine deck.

This is where the copying ended and original concepts began. The suspension with horizontal springs was rather interesting. There were six small road wheels per side, coupled into 3 bogeys. 

The biggest novelty was the method of building the hull. The major components were cast and bolted together. Only the floor plates weren't cast. This made assembly much easier.

The third prototype received a new upper hull and an early APX R turret.

Work on the prospective tank began in the spring of 1933. In June, the Conseil consultatif de l'armement (Armament Consultation Council) discussed the concept. Council members liked it. The tank was inexpensive and could therefore be built in large numbers. A contract for three experimental vehicles was signed on June 30th.

Hotchkiss' actions did not go unnoticed by its competitors, chiefly Renault. On August 2nd, 1933, the military composed new requirements for a light tank. The tank had to have 30 mm of armour and armament of either two machineguns or a 37 mm cannon. The requirements reflected Ainsworth's proposal, but included a turret. 14 companies, including Hotchkiss and Renault, participated in the resulting tender.

The Hotchkiss prototype turned out to be faster than the Renault ZM, but infantry command already made their choice.

Renault was one of the first to complete their task. Taking the small reconnaissance Renault VM tank as a foundation, they built a light tank called Renault ZM. By coincidence, this tank also had a cast hull. APX produced a similar design. The fast pace of Renault allowed it to break away from its competitors very quickly, despite a change in requirements made on May 22nd, 1934. The new requirements increased the thickness of the armour to 40 mm, enough to protect it from the 25 mm cannon. The top speed increased to 15-20 kph. The allowed mass also increased.

Hotchkiss presented their first prototype of a turretless tank only in January of 1935. A second prototype was produced a short while later. The tanks were rather unpolished, which showed at the trials held in January-May of 1935. Despite all their defects, the 8.5 ton prototypes ended up being 8-10 kph faster than the Renault ZM. This advantage was disregarded by the infantry command. On April 29th, 1935, the Renault ZM was accepted into service as the Char léger Modèle 1935 R.

Despite this, Hotchkiss produced a third prototype in August of 1935. It was similar to the first two, but had a new top. The driver was shifted to the right, and the commander, also the gunner and loader, was now placed in the APX R turret. This tank was tested in August-September of 1935. It also turned out to be faster than the Renault ZM.

However, the infantry already made their choice, favouring the Renault tank. In addition, they had the FCM Tracteur RN3, later accepted into service as the FCM 36. The Hotchkiss was the odd man out. This would have been the end of its story, if not for the cavalry.

A budget tank for cavalry

The French cavalry initially had no desire to purchase light tanks. Different vehicles were needed to equip cuirassier regiments: the AMC or Automitrailleuse de combat (armoured car). This type of vehicle, essentially a medium tank, was developed by SOMUA. With some alterations, the AC 3 was accepted into service as the Automitrailleuse de Combat modèle 1935 S on March 25th, 1936.

According to plans made on November 21st, 1935, 600 of these tanks would be purchased. However, the French cavalry was faced with two problems: production and finance. SOMUA was physically incapable of building enough tanks, and the cost of 982,000 francs apiece was astronomical. Several light tanks could be purchased for this much money. In late 1935 cavalry command turned its eye towards Hotchkiss tanks.

A pre-production tank, somewhat different from the mass production H 35.

It is hard to say that the light tank's characteristics were outstanding. It was half as fast as the AMR 35ZT, and its SA 18 37 mm gun could not compare with the 47 mm gun of the SOMUA S 35. Nevertheless, the tank had 1.5 times the performance of the Renault R 35, given the same protection and armament. The driver in the Hotchkiss tank also had better vision, and the tank was half a ton lighter than its competitor. The production capacity of Hotchkiss factories would allow for large scale inexpensive production to be set up quickly. Their cost would be a little higher than the Renault R 35.

Production Hotchkiss H 35.

The tank was accepted into service with the French cavalry in November of 1935 as the Char léger Modèle 1935 H, DIT. An order for 200 tanks was made, which were sent to the 1st and 2nd tank divisions. As a result of trials, a large amount of changes were made to the design. They were first tried out on the experimental tank, which received the registration number 8533-W1. The running gear (bogeys and drive sprockets) was radically altered. The number of return rollers was reduced to two. The hull was reworked with the aim of making production easier. The engine deck was redesigned to make access to the engine easier. The design of the turret changed slightly.

Diagram of the tank hull, showing what parts the tank consists of and how they are joined.

Production began after a few additional changes. Cavalry command was satisfied with the trials of the improved prototype and made an order for 100 additional tanks. Production vehicles received serial numbers starting from 400001. The first tanks were delivered in June of 1936. By French standards, they were produced at a decent rate. The plan for 300 tanks was completed in November of 1937. Later production tanks received vision devices that were less susceptible to enemy fire.

Production H 35. Camouflage was applied at the factory.

Infantry command ordered 100 tanks for themselves. They were produced in 1938. These tanks were used to equip the 13th and 38th tank battalions. Thanks to this, the infantry managed to save some money. Seeing competition, Renault was ready to make a deal. The cost of an R 35 tank dropped by 60,000 francs. 

As of September 1st, 1939, Hotchkiss tanks were included in 11 squadrons. The 12th squadron was rearmed with these tanks instead of the AMC 35.

The same tank from the left.

The SA 38 gun was developed towards the end of the 1930s. It allowed to defeat tanks with up to 38 mm of armour and could be installed in light tanks. However, it was only put into production in February of 1940. New tanks had the highest priority in receiving this weapon, but older tanks received it whenever possible, including R 35 and H 35 tanks.

This column of tanks is led by a commander's Hotchkiss tank, which is armed with the SA 38 gun and equipped with a radio. The H 35 tanks that follow still have the short gun.

Only a portion of the tanks received upgraded armament by the start of the war. Priority was given to platoon commander vehicles. A portion of these vehicles also had ER 29 radios. Another element that was added to a portion of the tanks was a tail for crossing trenches. More on that below.

An extra fifty horses

The Hotchkiss H 35 was noticeably more mobile than the Renault R 35, but it still lacked engine power. 75 hp was enough to follow motorized columns, but the tank could not catch up to the SOMUA S 35. Work on getting rid of this drawback began in 1937.

The altered hull of the H 35. The biggest change was the engine deck, which became noticeably larger due to a bigger engine.

Cars built by Hotchkiss won the famous rally at Monte Carlo four times in the 1930s. Special race cars were built for this purpose with 117 hp engines. One of these engines was also installed in a tank. The results were mixed. On one hand, the top speed increased to 45 kph, even faster than the SOMUA S 35. On the other hand, issues with the gearbox cropped up, as it was not prepared to deal with this power. The tank could drive fast, but not for long. The second issue was wear on the road wheel rims. The Hotchkiss designers solved the issue of mobility, but faced a whole new set of problems.

Overall layout of the Hotchkiss H 39.

The issue with peeling rims was solved easily. New road wheels were fully metallic. A new engine was designed based on the race car engine. It was also a 6 cylinder engine, but the volume increased to 5.96 L, giving it 120 hp of power. Since the new engine was very large, a new engine deck had to be designed to accommodate it. The mass of the tank increased from 11.7 to 13.2 tons, but increasing the engine power by 1.5 times improved the mobility noticeably. The top speed was 36.7 kph, about the same as tank's foreign equivalents. The increase in power had an effect on fuel economy. The tank's range decreased to 120 km from 150.

More than half of H 39 tanks received short SA 18 guns. These tanks are often called H 38, which is incorrect.

The altered vehicle was named Char léger modèle 1938 série D by the factory, however the index H 38 was never used. The tank was accepted into service as the Char léger modèle 1935 H modifié 1939 on February 18th, 1939. The first tank with serial number 40401 was delivered in March of 1939.

After the engine was upgraded, the infantry became the biggest customer of the tank they initially rejected. The cavalry received only 16 of H 39s by September 1st, 1939, while the infantry had 180 of them in 4 battalions (14 in reserve and 4 in repairs). 3 tanks were also sent to Poland in July of 1939.

Delivery of a batch of H 39 tanks with SA 38 guns, spring of 1940. These tanks already have tails which also housed a spare road wheel and toolbox.

Order for tanks increased with the start of WWII. The military wanted 300 tanks monthly, which was an impossible feat for the small Hotchkiss factory. In addition, Hotchkiss also had to build Laffly artillery tractors. Production of the H 39 ramped up very slowly. 20 tanks were built in September of 1939, by February monthly production grew to 69 units. Production of the 37 mm SA 38 began by then. In total, the French had time to produce about 800 of these guns. The H 39 had the highest priority for them. Out of 557 of these tanks built by May 1st, 1940, about a third had long barreled weapons.

By May 10th, the cavalry had 252 H 39s (50 in repairs or training units). The infantry had 271 (of those 48 in repairs or training units). Another two tanks were sold to Turkey in February of 1940.

Unused H 39 hulls and turrets, captured by the Germans. June 1940.

The peak of production was reached in May of 1940. 122 tanks were delivered. 33 more were built in June. In total, 710 Hotchkiss H 39 tanks were built. Together, there were 1110 H 35 and H 39 tanks built. Not bad for a tank that was initially rejected!

Best of the worst

The Hotchkiss and Renault tanks had the same armament and comparable protection. However, the H 35 and H 39 had the advantage of a more sloped front of the turret platform. However, this did not radically change the situation. The 3.7 cm Pak could confidently penetrate this armour at a range of up to 300 meters.

H 39 with an AMX suspension.

The greatest advantage of the H 35 and even more so for the H 39 was speed. It also quickly became clear that the R 35 behaved poorly off-road. Hotchkiss tanks performed much better. This fact did not stop the AMX from proposing a new suspension for the tank, the same as the one used on the AMX 40. After trials, this proposal was rejected. It was much more suitable for a slow tank.

Another improvement to mobility stuck. This was the tail that allowed the tank to cross trenches and ditches. Two types of tails designed by Hotchkiss and AMX were trialled in 1939. The first one was put into mass production. In addition to new tanks, older ones received this tail as an upgrade. The spare road wheel was moved on top of it. Some tanks also had their toolbox mounted there.

H 35 tanks driving to the front line, Ardennes, May of 1940.

H 39 cavalry tanks were used by tank squadrons, which were made up of 47 tanks. Infantry used these tanks in battalions of 45 tanks. During the war the tanks were used by units with a different number of tanks, usually less. The cavalrymen used them in armoured car regiments (Régiment d'automitrailleuses, or RAM), which had 16 tanks. 5 of these regiments were formed by May of 1940. Infantry had independent tank regiments 15-16 tanks apiece).

The cast armour offered reliable protection against 20 mm autocannons. 37 mm guns, however, could defeat the armour at 300 meters or less.

The Hotchkiss H 39 was one of the first French tanks to take part in full scale war against the Germans. This happened in early May of 1940 in Norway. The 342nd Independent Tank Regiment was sent north to possibly help Finland, but instead had to fight against their future allies. Out of 15 tanks only 5 took part in the fighting. 3 were lost. The surviving 12 tanks were evacuated to Britain, where they were used by the 1st Free French Tank Regiment.

Even though the H 39 was the best French tank, it had little effect on the course of the war.

The H 35 and H 39 were used actively during the fighting in France. Many H 39 tanks received long barrelled guns. These tanks were much more dangerous than the R 35 or FCM 36. The mobility of these tanks was just a bit less than that of the German light tanks. The weaknesses of these tanks included a lack of radios (only commanders had them), and the visibility was far from ideal. The concept of a small two man tank was already obsolete.

German light tanks were not that much better than the H 39. Unfortunately, the main strike force consisted of PzIII and PzIV medium tanks, as well as Czechoslovakian Pz 38(t) tanks. French light tanks compared poorly to these vehicles, and there were not so many French medium tanks. The French tankers fought fiercely, especially in the Ardennes, but the army lasted only for a month and a half.

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