In response to the requirement, the designers at Terni added a small sloping superstructure in place of the turret, actually increasing the available space inside. More armour was added to the vehicle, with the side plates being thickened to 30mm. Another increase in protection was achieved by the sloping plates that make up the superstructure, in place of the vertical faces of the previous turret. Due to the extra armour, the weight of the vehicle has increased, and the performances revised downwards.
The designers felt that a variety of other weapons could also be accommodated. The 75/18 howitzer is interchangeable with the 47/32 and could be mounted in the turret or fixed emplacement. Due to the greater space available in the self propelled gun, it was also thought possible to fit a longer 75/32 gun which has better performance.
S13/38
Crew: 3
Weight: 13,400kg
Length: 4.92m
Width: 2.20m
Height: 2.22m
Engine: 300hp Isotta-Fraschini L1506
Armament: 1 x 47/32, 1 x 8mm Breda
Armour: 40 - 10mm
Performance: 40mph top speed, 160mile range
P/W: 23hp/ton Ground Pressure: 10.5psi