Carro Armato P 40

The P40 was an Italian World War II tank design. It was armed with a 75 mm gun and an 8 mm Breda machine gun, plus another optional machine gun in an anti-aircraft mount. The official Italian designation was Carro Armato ("armored tank") P 26/40. The designation means: P for pesante (Italian: "heavy"), the weight of 26 tons, and the year of adoption 1940.

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.

History
Although designed in 1940, the first prototype was not completed until 1942. The initial plan was for a 25 tonne 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 required, and the Italian tank industry (i.e. the duopoly Fiat-Ansaldo) 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 petrol engine was eventually tested.

The design of the P40 was originally similar to tanks such as the M11/39, but with a bigger gun and more armour. After learning about Soviet T-34s in 1941, the armour of the P40 was quickly re-designed, adopting more markedly sloped plates, and the new gun was adopted. The gun designation "75/34" referred to a 75 mm bore diameter gun with a length equal to 34 calibres. It was used in lieu of the 75/18 gun, with a shorter barrel of only 18 calibres. 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.

Design
The turret was operated by two crew members and this was a significant drawback as it put excessive workload on the tank's commander. At that time, most new tanks were designed with three-man turrets, following the successful example of the German Panzer III.

The main weapon was the 75/34 cannon, a development of the Model 37 divisional gun (34 calibres long), retaining the same dimensions. This weapon had a muzzle velocity of around 700 m/s. The main gun was normally provided with around 75 rounds of ammunition. 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 lower, only around 600 rounds, compared to 3,000 of the "M" series.

The mechanical systems were a development of the "M" series, in particular the suspension which was reliable, but in rough terrain would not allow speeds similar to the more modern Christie suspension or torsion bar suspension. Nevertheless, the good power-to-weight ratio represented a significant improvement in mobility over its predecessors.

The armour, quite resistant by Italian standards, 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. Compared to welded armour, riveted armour is vulnerable to breaking apart at the joints meaning that even quite resistant plates can be defeated by rivet failures. The front armour had a compound slope with a best facing of 50 mm/45 degrees.

The armor 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).

The P40 design was reasonably up-to-date, but the tank was without some modern features such as welded armour, adequate suspension, and a cupola for the commander. The P40 was designated as a heavy tank in Italy, not because of its weight, but because of the intended role: it was to accompany and support the widely used medium ("M") tanks on the battlefields. Its weight, armor and armament would classify it as medium tank in Wehrmacht or other contemporary armies. 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. It was the final evolution of Italian tank designs, that begun with the Vickers-based tankettes (such as the CV29 and L3/35) and developed into models such as the M11/39 medium tank, a much heavier construction whose internal design shared many characteristics of the earlier tankettes.

Production
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.

Variants
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 about 100mm of frontal armour and a main armament of either a longer-barrelled 75 mm gun or the same 90 mm piece mounted on the Semovente M41 90/53. However of this variant only a couple wooden scale models were ever produced. There was also a further upgraded variant called the P43 bis which was planned to have a 480 hp gasoline engine.

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 Royal 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.