This was considered the most effective artillery piece in service, and in several versions was used as an anti-aircraft and anti-tank gun by the Army and the Navy. To be more effective in its new role, the size of the gun was increased from 90 mm (3.5 in) to 102 mm (4 in), a non-standard Italian artillery calibre, and fired shells weighing 13 kg (29 lb) as opposed to the standard gun's 10 kg (22 lb), with a muzzle velocity of over 600 m/s (1,970 ft/s).The gun together with its recoil system weighed 1,500 kg (3,300 lb). Due to it being a re-bored smaller gun, its weight was relatively low for its calibre. The P.108A concept was in line with other contemporary developments, as medium bombers such as the North American B-25 Mitchell and even smaller attack-aircraft like the Henschel Hs 129 were being fitted with high-velocity 75 mm (3 in) guns. The gun was mounted longitudinally in the fuselage centreline, at a depressed angle, and had a powerful recoil, which the 27 tonne (30 ton) airframe was able to absorb. The amount of ammunition that could be carried was around 50-60 rounds for the main gun, as well as up to three standard torpedoes or two radio-guided torpedoes (a secret weapon which was never used in combat), and for the defensive wing and fuselage turrets. The 102 mm (4 in) gun was intended to be fitted with a ballistic sight with an analogue computer, and a six or 12 round mechanical loader. Initial modifications were made to MM.24318 which on 16 December 1942 flew to Savona. The modifications were completed in February 1943, and testing commenced on 3 March. Testing of the P.108A was satisfactory, achieving a maximum speed of around 440 km/h (270 mph) due to aerodynamic redesigning. It flew to Furbara on 19 March, and later to Pisa on 16 April, where it carried out a series of firing trials at altitudes between 1,500 and 4,500 m (4,900 and 14,800 ft) to collect the ballistic data that was required to allow the computing gunsight to be produced. After totalling 24 hr, 40 min of flight and weapons trials, it returned to Albenga. It was presented as the new official attack machine at Furbara on 22 May, and it was planned to build five further P.108As, as well as converting between five or possibly all P.108s available. But