[3] Design had started in 1940 but very few had been built by the time Italy signed the armistice with the Allies in September 1943 and the few produced afterwards were used by the Germans.

After learning about Soviet T-34s in 1941, thanks to a captured tank supplied by the Germans, the whole design was radically modified: the armour was quickly thickened (from 40 to 50 mm on the front and from 30 to 40 mm on the sides) and re-designed, adopting more markedly sloped plates, and the new 75/34 gun was adopted; meanwhile the dual barbette mount in the hull was deleted.

[3] Only a few (between one and five depending on the source) pre-production models were completed in the months before the Italian Armistice in September 1943, at which point they were taken over by the German Wehrmacht.

About a hundred P 40s were used by the German military, of which about 40 were without engines and used as static emplacements at defensive positions such as the Gustav and Gothic Lines.

This was one of the fantasious projects products in that last spots of the war by many chiefs of Republican Fascism, like the one conceived by Pavolini about the so called "Ridotto" of Valtellina.

In Milan, as a matter of fact, it was planned to concentrate the majors of Fascism in the area of Corso Monforte an Via Mozart, where there were the Prefecture and the command of the Black Brigades, and, for this reason, the little group of tankers of "Leoncello" received two P40 tanks from Germans, who also trained them for a little.

The tanks were abandoned by their crews during the insurrection of April 25th and at least one of them was re-used by partisans during that day (with a big and evident comunnist symbol painted on it).

[10] For secondary armament, the P 40 had a co-axial machine-gun and another which could be used in the anti-aircraft role, eschewing the traditional dual mount in the hull; the standard ammunition load was also lower, only around 600 rounds, compared to 3,000 of the "M" series.

There were at least two planned variants of the P 40, developed from early 1943 when the Italian Army realized that the tank was inferior to other designs such as the German Panther.

[4] In September 1943 Fiat and Ansaldo began development of a new design which could be comparable to the Panther, and the result was the P 43 bis, with heavily sloped armour, a 450 HP engine and a 90/42 gun.

This gun was produced in very few numbers, and the Italian artillery remained equipped mainly with obsolete weapons for the duration of the war.

Due to its mass, it was quite bulky to move, and so it was decided to build a self-propelled version, utilizing the most powerful of all Italian military vehicles.

All space of the P 40 hull was dedicated to supporting the gun, so the ammunition and crew would have required additional vehicles to be moved.