The tractor unit of the St Chamond SPG was much the same across all the various models of SPG. The main difference between the SPG version tractors were the shell racks at the rear of the tractor. The power train was similar to the St Chamond tank with a Panhard petrol engine of 120 h.p. coupled to the Crochat-Collardeau transmission with an external 50m power cable fed power to the gun vehicle. When travelling on roads a 2m steel drawbar was used to link the tractor and gun vehicle, off road the two vehicles were only linked by the power cable. Designer M Bergman