In June 1940 when the Italians entered the war officially, the way to staff exchanges and a close observation of German ideas was opened. A senior Italian artillery officer, Colonel Berlese, noted the success of the StuG III in the French campaign and put forward the suggestion that the Italian armoure divisions should have a similar type of vehicle based on their won successful medium tank, the M13/40. He proposed that the standard Italian 75/18 gun howitzer be utilized. In December, 1940 Ansaldo-Fossati at Genoa were asked to produce detailed design and they quickly produced a wood mock-up of the proposed superstructure and gun on a M12/40 hull and running gear. The practicability of the idea was proven, and an opening order of 30 vehicles was placed almost at once. The first actual running prototype was ready within a month of the order, on February, 10th 1941. It was delivered to the army for tests by Motor Technical and Ordnance departments and proved very satisfactory. The order was immediately increased to 60 vehicles and all were delivered in 1941, most going to the Italian divisions in the Western Desert.
Internally, the Semovente M40 da 75/18 was almost identical to the M13/40. The motorwas a Spa 8T V-8 diesel engine giving a maximum road speed of 20 mph and a cross country speed of 9.5 mph. The vehicle had epicyclic steering and shaft and sliding gear transmission. The main armament was set in a ballmount in the boxy superstructure, and there was a distinctive perforated flash eliminator and muzzle brake.
The ball or gimball type of mounting had both vertical and horizontal mountings, and the hemishperical mantlet was 50 mm thick. The gun was elevated by a handwheel with maximum elevation of 22 1/2 degrees, and a maximum depression of 12 degrees. Traverse was also controlled by handwheel and worm and spur gears, giving a maximum of 18 degrees left and 20 degrees right.
The loader, stationed behind the driver, acted as a wireless operater. Third member of crew was the commander who was also gunner.
The Semovente proved the most successful of Italian tracked AFV's in World War 2. It was simpler to build than the tank on which it was based, and its low silhouette was a tactical advantage.
Several models of the Semovente were produced, generally speaking the changes followed those made in the tank chassis on which it was built. Vehicles built in 1942 were on the very similar M41 chassis (M14/41). In 1943, the chassis was switched to that of the M42.