The SAu 40 was developed by SOMUA between 1935 and 1937 alongside the S.35 tank for French cavalry. It featured a redesigned hull to house a 75 mm cannon and a new commander's cupola with a machine gun. The prototype was finished in 1939 after delays in acquiring the cannon. It is uncertain if more vehicles were produced or if it saw combat action. Doctrinally, the vehicle was relegated to a support role, intended to provide cover for heavier tanks like the Char B1.

It was introduced in Update 1.75 "La Résistance". It distinguishes itself by its very tall cupola and thick gun barrel. This tank is equipped with APHE rounds, a rare feature in the French tech tree. As it was developed from the French S.35, this tank shares many of its characteristics such as the ~40 mm thick cast hull bolted onto the chassis, which is barely a widened version of its original. The track system is mostly the same as on the S.35, with 25 mm plates covering the roller wheels. As for the hull, it's a widened variant of the S.35's hull with two 8 mm grilles over the engine compartment and doors on the side. The tank features an APHE shell, this increases the chances of one-shots at enemy tanks. In terms of mobility, it is a pretty slow tank, and it's not very survivable either, it has a very large profile and the commander's cupola is a big weak point that can be exploited by other vehicles.