The problem of moving artillery in support of any advance across the trenches on the Western Front was identified by the French Army as a central issue in 1915. The inability of horse drawn or wheeled vehicles to traverse the terrain of no-man's land and shell cratered trench systems was obvious which left only tracked vehicles as a viable alternative. French industry prompted by the Ministry of Munitions and Army High Command explored just about all possible options for moving artillery with tracked vehicles. Some of these studies resulted in vehicles which were placed in production such as the Renault FB artillery portee vehicle and the Schneider CD heavy towing vehicle. Although these vehicles mostly solved the problem of transporting artillery over bad ground it was clear there was still a delay once artillery pieces had been delivered before the artillery could go into action due to the set up time. The St Chamond SPGs offered a solution for bringing heavy guns into action quickly, although to modern eyes a speed of 2.5 km/hr requires a redefinition of "quickly". There remained a similar problem for light field guns and howitzers.
The start of production of the light Renault FT tank in 1917 offered a possible solution to the deployment of light field guns on tracked vehicles based on the FT chassis. By May 1918 studies were underway to use turretless FT tanks with light guns such as the 75mm Mle 1897 field gun and 105mm Mle 1913 howitzer fitted. At the end of August 1918 the French Army GHQ received and approved these studies. On 3 Sept 1918 a specification was issued for a vehicle based on the Renault FT with the 75mm Mle 1897 field gun with a crew of 4 (driver plus gun crew), carrying 100 rounds of ammunition and a total weight of 5 - 6 tonnes. In response to the specification three prototypes were built. The intent was to construct an SPG which could be used for counter-battery fire and in an anti-tank role.
The first SPG produced was designed by Renault and tested by them in August 1918 and handed over for official testing at Bourges, the French Army proving ground, on 18 Sept 1918. The vehicle was extremely minimal. The gun was limited to fire over the rear of the SPG and could only be moved in the vertical plane (-4° to +24°) which limited the max. range of the 75mm gun, there was a control which allowed the whole vehicle to be turned for gun traverse, the details of how this worked are unknown. The driver had to exit the vehicle before firing and the accommodation for the two man gun crew was an unprotected pair of seats on top of the SPG. 40 rounds of ammunition were stored in boxes on top of the engine compartment. Although the Renault SPG was found to be quite stable and met the criteria established for mobility over bad ground the poor ergonomics and smaller than specification ammunition capacity meant it was rejected by the French Army.
A video of the Renault SPG has recently (Dec 2013) been released by CNRS (French Army Archive) which shows the Renault SPGs being demonstrated. (Please note the video may be slow to load).
Renault also experimentally fitted a 105mm howitzer to an FT tank chassis. Very little is known about this version but the upper part of the hull seems to have been extensively modified to fit the howitzer.
With the rejection of the Renault SPG, Army Headquarters requested that the "section technique automobile de Vincennes" (STAV) study an SPG with capacity to carry 150 rounds of ammunition (half a day's firing) and using the Gramme naval mounting for the 75mm gun. The front of an FT chassis was cut down and the gun mount installed on the reinforced floor of the chassis. The driver was relocated to the centre of the vehicle, similar to the unsuccessful Renault prototype for Renault FT 75 BS. The gun crew had a unprotected bench across the rear of the chassis. The prototype was built by Renault and had a 360° traverse and elevation -8° to +40° although at elevations above +10° the gun had to be fired over the rear of the vehicle. The ammunition capacity was 120 rounds. The first, and only, prototype was finalised on 9 Oct 1918.
The last FT SPG design was that of the "section technique de l'artillerie" (STA) which had been studying SPG design since May 1918. This was a much more elaborate design with the engine moved to the centre of the chassis and the driver also in a central location. The rear of the FT chassis was opened out to create a platform for the gun crew and the gun was mounted to fire over the front of the vehicle. The gun could be elevated from -5° to +41° with 11° of traverse. The SPG could carry 90 rounds of ammunition. The SPG appears to have been built by Renault and was sent to Bourges in late October 1918. Later modifications to the STA SPG included extending the rear platform, adding a folding spade to prevent movement of the vehicle during firing and the addition of a Hotchkiss MG presumably for local defence.
One of the problems with operating SPGs with quick firing guns was that of ammunition supply. Renault produced a prototype of a tracked munitions vehicle with a central drivers position and an open compartment with a hinged gate at the front. The volume of the compartment was 1.5m x 1.05m x 0.9m. The track spacing was slightly increased compared to the FT tank. Only one prototype was produced but it's hard to see a role for such a vehicle when the existing Renault FB and Schneider CD could carry much more ammunition.
The STA/STAV SPGs fell foul of politics. General Herr, Inspector General of Artillery, opposed the SPGs since he believed that towing guns with tracked tractors was a better solution. He managed to convince Gen Pétain, the commander in chief who opposed the production of a trial batch of 4 SPGs proposed by the Ministry of Munitions on 6 Nov 1918. However, the SPGs had supporters. General Sainte-Claire Deville, Inspector General of Ordnance, strongly supported tracked artillery in Dec 1918. Pétain avoided a confrontation by calling for more studies of the competing views. By the time these were completed the war was long over and the FT tank was considered to be close to obsolete so proposals to build enough STA and STAV SPGs to properly evaluate them were never taken up.
The primary information for this article came from:
François Vauvillier "1916-18 des Chenilles pour le 75" in "Histoire de Guerre Blindés & Materiel" No. 89, Oct-Dec 2009, pp.70-74.
There are very few images of the Renault SPGs available especially of the STAV and STA types - the period images have been taken from the cited source.
As far as is known no models exist of the Renault SPGs