P40 heavy tank
Although designed in 1940, the first prototype was not completed until 1942. The initial plan was for a 25 ton. tank with a 75 mm gun and to be named P26. The development work proceeded quickly except for the engine; the Italian military staff, the Stato Maggiore, wanted a diesel power-plant, while the builders favoured a petrol engine.However, in Italy at the time there were no engines (diesel or petrol) available capable of developing the 300 hp (220 kW) required, and the Italian tank industry did not turn to easily available aircraft engines for its tanks as the contemporary U.S. and British tank manufacturers had done. The design of a new engine was very slow and in the end a 420 hp (310 kW) petrol engine was eventually tested.
The main weapon selected was a 75/34 cannon ("75/34" refers to a 75 mm bore diameter gun with a length equal to 34 calibers). The design of the P40 was originally similar to tanks such as the M11/39, but with a bigger gun and more armour. After encountering Soviet T-34s on the Eastern Front, the armour of the P40 was quickly re-designed, adopting more markedly sloping plates, while the gun was enhanced, with the adoption of a new weapon that had the same dimensions as the Model 37 divisional gun (34 calibres), from which it was developed (as had already been done with the 75/18 mm gun, originally a divisional artillery weapon as well). This weapon had a muzzle velocity of around 700 m/s, similar to many other tank guns of the time, but inferior to the longer 75 mm German guns (both 48 caliber and 70 caliber models) such as in the Panther tank (a contemporary of the P40), whose design was also influenced by the T-34.The tank's armour was sloped and 60 mm thick at the turret front and mantlet (by comparison the M13/40 had 42 mm), but it was still riveted at a time when most tanks were constructed by welding. The sloping wasn't comparable to the T-34's, as the front armour had 50 mm/45 degrees as opposed to 45 mm/60 degrees of the T-34. The turret was still operated by two crew members (similar to the T-34/76) and the mechanical systems were a development of the "M" series, in particular the suspension was still similar. The suspension allowed for good reliability, but its speed was usually much lower than other models like the T-34 with its Christie suspension.
One shift in the design was the number of machine-guns which was much lower than on the "M" series. The P40 originally fielded three machine guns, but one was removed along with the deletion of the frontal, dual barbette machine gun mount. The standard ammunition load was also lower (only around 600 rounds, compared to 3,000 of the "M" series and most other World War II tanks). The main gun was normally provided with around 65 shells (the T-34 and the Sherman had around 90). The main role of the P40 shifted from infantry support to anti-tank warfare, and all the internal space was dedicated to this end, making the vehicle rather cramped.The P40 design was reasonably up-to-date, but the tank was without some modern features such as welded armour, reliable suspension, and a cupola for the commander. The armour, quite resistant by Italian standards, was capable of protecting the tank against early anti-tank guns such as the British QF 2 pounder (40 mm, 1.6 in), but was vulnerable to 1943 anti-tank weapons such as the British QF 6 pounder (57 mm, 2.24 in) and QF 17 pounder (76 mm, 3 in) which were capable of piercing more than 100 mm (3.9 in) of armour at typical combat ranges.
Despite its shortcomings, the P40 was the only Italian tank design that was comparable to Allied and German medium tanks as they appeared in the middle of the war. With a weight of around 25-30 ton., this tank, a few years previously, would have fallen into the 'heavy' category. Designs like the M13/40, were, at 10-15 ton., regarded as 'medium'. The P40 was designated as a 'heavy' tank but by international standards, it was only a medium tank. It was the final evolution of Italy's tank designs, that was begun with the Vickers-based tankettes (such as the CV29 and L3/35) and then evolved in further models (such as the M11/39 medium tank, whose internal design shared many characteristics of the earlier tankettes, but which was of much heavier construction).Of the 1,200 tanks ordered, only a few (between one and five depending on the source), pre-production models were completed before the Italian Armistice in September 1943, at which point they were taken over by the German Wehrmacht. About a hundred P40s were built by Ansaldo from then until the end of the war, although most were not entirely completed because of a lack of engines. A few were used in combat, under the German designation of Panzerkampfwagen P40 737(i), for example at Anzio. Some, without engines, were used as static strongpoints.
There were at least two planned variants of the P40. One was named P43, a tank with a weight over 30 tonnes, which would have had circa 80mm of frontal armour and a main armament of either a longer-barrelled 75mm gun or the same 90mm piece mounted on the Semovente M41 90/53. However of this variant only a couple wooden models in scale were ever produced.The other project was the Semovente 149/40, based on the P40 hull. Only one of these vehicles was ever built. It was intended to be a highly mobile self-propelled gun, and its armament was the most powerful in the Italian Army. A 149 mm / 40 calibre artillery piece with a range of over 23 km (slightly more than that of the US M1 Long Tom). 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 P40 hull was dedicated to supporting the gun, so the ammunition and crew would have required additional vehicles to be moved. The gun would have been ready to fire in three minutes from coming to a stop, compared to the 17 minutes required by towed artillery.Work on the Semovente 149/40 started in 1942 and the prototype was tested in 1943, but the Italian Army was not very impressed. After the Armistice the vehicle was acquired by the Germans, and they weren't impressed by it either. Finally American forces captured it during the invasion of Germany and sent it to the Aberdeen Proving Ground for testing. Except for the suspension, the rest of this self-propelled gun probably inspired the American M107.