Renault FT 75 BS

39 made 1918

In 1918 the French Army staff was enthusiastic about the Renault FT and ordered perhaps 5000 vehicles in several variants for the great offensive planned in the spring 1919. It was declined alreadi into multiple variants like a communication vehicle, and it was felt a version with a beefier gun would be needed for the more serious fortinfication of the Hindendburg line. After a few prototypes, some 970 Schneider 75mm howitzers were ordered as 'Char FT 75BS' designed for having a more powerful weapon to demolish obstacles and carry a bridge to facilitate passage of remaining tanks, gap walls and large anti-tank trenches. A distant cousin of WW2 Chuchill AVRE Petard bridgelayer. With the German capitulation, only 39 were received before the order was cancelled. They were in part still in service by 1940.

Development

The Renault FT was a successful design, the most mass produced in the first world war and for many authors, a game changer in tank warfare. It introduced classic recipes with a driver forward, central fighting compartment with turret in the middle and engine compartment at the rear. It equipped the French Army, the US army (with the M1917) and spawned copies across the globe, Russia, Japan, Italy... Many still fought in WW2, in French, Belgian, Finnish, and Yugoslavian service among others, plus those used by the Werhmacht for training driver and anti-partisan warfare. In total, 2100 tanks were completed with machine guns, 1,246 with 37mm cannons for close support, 188 TSF (communication tanks), and 155 training vehicles, plus, for what we are concerned, 39 75BS.

The need for a bigger gun than the short barrel 37mm Puteaux M1917 cannon emerged from the encounter of more beefier German defenses, using notably concrete in their rear échelon trench networks. Allied aviation since a while observed preparations on the German border proper of a new set of fortifications included antitank trenches and obstacles against tanks for the first time, but also concrete blockhaus. Tests with the 37 mm showed these needed a lot of shells to be put out of action. The 37 mm originally was designed to deal only with open air MG nests. Some also expressed the need to cram a machine gun to complement the 37 mm gun, but it was impossible in the tiny turret.

So both to deal with heavier fortifications, vbefore the arrival of heavy artillery, having a mobile tank with a larger gun was needed, and iof possible with a coaxial machine gun to deal with infantry; which necessary imposed a larger turret. General Estienne, the "father of the French Tank Corps" specified such vehicle, initially havionf no mechanical chassis, to be developed on the nimble, cheap and proven chassis of the Renault FT. Being an artillery officer he also piked up the 75mm Blockhaus Schneider (BS) as the best fit due to its compact dimensions, but after modifications to make it even shorter.

The 75mm BS was originally a short range fortress gun which saw used already on the Schneider CA1 tank, plced inside a ball mount for maximal elevation and training. This was a short range ordnance but thanks to its small dimensions and light weight coupled wirth the same high rate of fire as the 37 mm (it was semi-automated for one man) it soon appeared ideal as support gun to be mounted on the FT tanks.

Under Estienne supervision, which passed the specifications to Louis Renault and Metzmaier, the conversion, once the basic design was approved, was quick. Two different prototypes were built and tested in 1918. The Renault design team made a self propelled gun essentially, with the same 75 mm gun in the same ball mount as for the Schneider CA1, but moved forward, whereas the driver was reloacted to an elevated position in the center, seeing through a small "conning tower". The gun was mounted low and its unclear how the gunner was to operate while seated in that such restricted space, especially to access rounds. The prototype was narrow but quite tall and thus, found to be overweight with poor agility and the blind spot for the driver of the road or any obstacle below. The work of the gunner and loaded was never made clear. Thus, the design was quickly rejected.

A new approach was needed. A second prototype was built, not in Renault but at Champlieu which was a technical organization with workshops with the armament commission. These military engineers simply choosed a large turret-shaped casemate design to accomodate both the new gun and a coaxial machine gun, and thus giving some space in the fighting compartment while preserving the driver's view. The only catch was that apparent turret was too large to fit inside the former ring mount, and thus was simply made fixed. Weight increase was 200kg and in the compartment enough space was found to cram 35 rounds. The commission headed by Estienne greenlighted the concept as Renault "FT 75 BS".

600 of the new support tank were ordered in mid-May 1918, so to provide each FT section already mixing "male and female" (gun/MG armed) FT tanks, a single FT 75 BS. To the French parliament, it was justified by the expected replacement of 50% worn out surviving Schneider CA1 tanks. The first production FT 75 BS only came out by late July 1918. By the time they were enough, the allies made their post-Kaiserschlacht counter-offensive (after the failed spring 1918 German offensive). However conversions were slow with many bottlenecks causing delays and only 11 had been delivered when the order was cancelled on 18 November 1918. None saw action, and another 29 well advanced on the factory floor were delivered as well in 1919. Thus, in the absence of combat use, their combat record stays unproven.

Design

The idea of cramming even the short barrel 75 mm into the Renault FT only led to design a self-propelled gun solution, in which the gun only traverse and elevation would be procured by the existing ball mount. Due to the small turret ring which cannot be modified, there was no way to fit the new gun inside a regular, working turret. Instead a fixed casemate was designed, which rested on the hull itself. The ring was still there to allow the crew to operate, two men, the commander/gunner and a loader. For the first time, the FT was a three-men crew tank, albeit in very cramped conditions.

The casemate was to be large enough to accomodate the main gun and provide sufficient room for the commander and loader, there was a two-hatch door on its left side for direct access and exit, and another roof hatch hinged at the back. The vasemate hd an extension aft, and inside were placed a few ready rounds, the rest being crammed inside the hull, passed on by the crouched loader below. The commander stood and operate the gun alone. The ball mount authorized some traverse and elevation, and the driver could be ordered to shift the vehicle left and right for more leeway. It should be noted that ball mpunts are common for machine guns but excessively rare for guns, especially of that caliber (3-inches) due to the weight and friction. The bearings needed to be generously spread with greese.

The howitzer was below L/10 caliber, with a Barrel Length equivalent to L/9.5. The ball bearing authorized up to -10° to +30° in elevation and 60° in traverse. It fired a 5.55 kg shell at 200 m/sec to a best range at 2,100 m, 600m effective. It had a particular breech system that authorize rapid loading, and ended with a metal extention behind to be easier to manipulate by the gunner. The massive smoke was naturally aspited by openings in the roof, but it could have been useful to open the hatch above and semi-opening those on the sides.

The other point was it was supposed to carry a bridge to facilitate passage of remaining tanks across any gap and trenches. Indeed it was supposed to be a support vehicle with studies on how to tow sleds, trailers and bridged. Indeed the FT had a trench crossing tail, but it was so small as not being able to cross the late-war German antitan trenches of the Hindenburg line. Estienne thus thought about providing each section with a bridge carrier that would allow the rest to follow. It was different from the fascine solution of the British tanks, and probably more advanced.

However the FT being still small, the bridge carried as also limited in size. The concept was thus that the FT would not carry but tow the bridge behind, specifically a FT 75 BS. It would be then dragged bt a chain copnnected to a winch driven by the engine, brought above and then in front, then dropped off, attached to the front by linkages outboard of the idlers, suspended by wire ropes and placed across the trench. The front was dropped by releasing the wire ropes and reversing the tank to disengage the bridge from linkages. Nobdy know how it was to fare in battle, as this system was never deloyed in operations. Early production 75 BS had hitch points to allow the bridge to be linked behind the idlers with chained guided by channel frames built over the superstructure to guide the wire rope holding the bridge before deployment. Although abandoned, the bridgelayer concept was not, and trials were made in the interwar already.

The other BS 75mm: Char Peugeot

The Char Peugeot 1917, also known as the Peugeot Tank, was an early French tank developed during World War I, lesser-known compared to the more famous Renault FT and Schneider CA1. It was developed by the French automobile manufacturer Peugeot as a private venture and counterweight to arch-rival Renault in a prospect of future mass orders. The design was part of France's effort to produce effective armored vehicles for trench warfare during World War I. Only a single prototype was built in 1917, intended to be an alternative to other French tank designs of the time. Its estimated weight of around 12 tons for 5.8 meters in length, 2.31 meters in width, and 2.24 meters in height. It was beefier than the FT but shorter.

Its primary armament was not a 37mm Puteaux SA 18 gun in a rotating turret, but the BS 75mm gun, and a coaxial 6.5 mm Hotchkiss. Front armour thickness was superior at 16mm, providing protection against small arms fire and shrapnel. It was powered by a 4-cylinder Peugeot engine rated for 100 horsepower, for a top speed of 12 km/h. It had a suspension system with vertical coil springs to improve cross-country mobility. When exaimined by the Versailles purchasing commission it was however rejected as not bringing a significant advantage over the Renault FT, which was solidified as the standard French light tank. The prototype underwent trials and evaluations and was deemed less practical.

The BS 75 in action

Captured Renault TSF and 75 BS examined by German troops side by side in June 1940.

Not in 1918, as they arrived late for training and were thus never deployed. But they were kept in the interwar in reserve, and did saw action, like the Renault TSF (Communication tank) organic as part of tank platoons in may 1940.

Specs Renault FT 75
Dimensions	Like FT but taller
Total weight, battle ready	200 kgs more than FT
Crew	3: Commander/Gunner, loader, driver.
Propulsion	Like FT
Speed	Like FT
Range on/off road
Armament	Schneider 75 mm BS Howitzer
Armor	Like FT
Total production	39 (970 ordered)