In response to a request in November 1942, the P.108A Artigliere "gunship" was developed for anti-shipping duties as an alternative to torpedo bombers. It was armed with a modified high velocity Ansaldo 1941 model (90/53 mm) gun mounted in a redesigned nose. This was considered to provide the best combination of precision and range of all Italian artillery, 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 (30 lb) as opposed to the standard gun's 10 kg (20 lb), with a muzzle velocity of over 600 m/s (1,970 ft/s). This weapon has only been superseded in calibre, on aircraft, by the low velocity 105 mm (4 in) modified M102 howitzer (23 calibres in length) carried on a mobile mounting in the flanks of the AC-130's 3.2 m (10.5 ft) wide fuselage. 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 was not particularly unusual at the time, as medium bombers such as the North American B-25 Mitchell and even smaller attack-aircraft like the Henschel Hs 129 were fitted with high-velocity 75 mm (2.6 in) guns despite being one or two categories lighter.
The gun was mounted longitudinally in the fuselage centreline, at a depressed angle, and had a very strong recoil action which the 27 tonne (30 ton) airframe was nevertheless 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 finally the standard defensive weapons in the fuselage and wings. 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, Villanova d'Albenga airfield. 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 the more aerodynamic redesigned nose. 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 for negative angles of elevation 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. Enthusiasm was high when 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 convert another five or possibly all P.108s available. But on 29 June, it was decided to produce no more than five aircraft, and in July, the order was further limited to two, and eventually cancelled. On 6 and 8 September, the lone P.108A made other weapons tests over the sea, finally equipped with the S.Giorgio calibration/aiming system. German forces took control of the P.108A and painted it in their insignia, but it was damaged soon afterwards by Allied bombing. Repaired by 7 April 1944, it finally flew to Rechlin where it was probably destroyed in one of the many Allied bombing raids.
Although the P.108A proved to be capable, and fired over 280 shells in testing, the Armistice and the never-ending change of priorities halted its development. The use of such large aircraft in a dangerous anti-ship role was however questionable (at sea level 360 km/h (220 mph) was the best safely achievable), the cost was even greater than standard bombers, and the improved naval anti-aircraft defences (Bofors 40 mm guns, P-F shells, and fire-control radar) led Germany to rely on (relatively) long-range missiles like the Henschel Hs 293 and Fritz X. These were much more effective, as was demonstrated on 9 September 1943, when the Italian Navy was attacked by their ex-allies. The Germans launched a number of missiles against the Italian battleships, sinking the Roma and damaging the Italia, causing over 1,300 deaths. The three armoured decks of RM Roma could withstand hits from battleship-calibre guns, with over 200 mm (7.9 in) thickness overall, so such results were well outside the capabilities of a medium calibre gun, even when air-transported.