The armored forces of the Italian Army comprised, in the interwar period, three main types of tanks: light tanks, breakthrough tanks and heavy tanks. Leaving apart the Fiat 2000 heavy tanks, of which only two exemplars were built, the remaining units were practically based in only two realizations: the L 3 light tank and the M 11/39 breakthrough tank. While the former was not more than a protected and self-propelled machine gun position, the latter had the purpose of breaking the enemy lines to allow the shock infantry to cross them. Because of this it had been fitted with an armament that until then seemed adequate: a 37/40 cannon and two 8-millimeter machine guns. But it was soon evident that the cannon was not actually sufficient for developing the required volume of fire, and because of that it was decided to replace it by a more powerful one which, besides, were not placed in a fixed position, unlike that of the M 11/39. From these premises it was born in the Ansaldo factory the M 13/40 tank, which was presented as a prototype in February 1940 and serially produced from the summer of that same year. The tank, which had the same mechanics than its predecessor, differentiated itself by the enhanced engine and the totally renovated upper part of the hull; the armament and the armor had been notably enhanced as well. To begin with, the cannon, replaced by a 47/32, was installed in a rotatory turret, while in the hull there were two Breda 38 8-millimeter machine guns, installed in a swivel mounting to the right of the driver. A third machine gun was installed in the turret, co-axially to the cannon, while a fourth one could be installed in the top of the turret for anti-aircraft purposes. The hull was formed by steel plates riveted to a solid profile framework. The turret, orientable in 360 degrees, could be maneuvered either by hand or through an oleodynamic servomechanism. In the interior of the tank there was a Marelli RF-1-CA transmitter-receiver. It should be mentioned that when this tank entered service in North Africa, in the autumn of 1940, it was perfectly able to resist the encounter with the enemy tanks, keeping this balance of forces for about twelve months. Only because of the entry into service of the heavier American tanks obtained by the British through the Lend and Lease Act, the M 13 was inevitably surpassed. Also two other models were developed from this tank: the M 14/41 and the M 15/42. The first one would differ from the M 13/40 only by the enhanced engine, whereas the second one would be fitted with a gasoline engine instead of a Diesel one, and the 47/32 cannon would be replaced by the 47/40, which had a higher muzzle velocity and, therefore, a higher piercing power. Unfortunately, the armor would always reveal itself as excessively light against the enemy anti-tank cannons (which were of larger caliber than the Italian ones) and the tank crews would try to compensate this lack by covering the front of the hulls with sand bags and fragments of spare tracks. After having fought in Africa, where they showed themselves as an effective weapon in overall terms, the M 13/40 took part in the encounters for the defense of Rome after the 8th September 1943. The remaining exemplars equipped the armored troops of the Italian Social Republic. After the war, some of these tanks served with the new Italian Army and with the police, in this case with the cannon replaced by an 8-millimeter machine gun.