Piaggio P.108A - Part one

Answering to a request made in November 1942, the P.108A "Artigliere" was developed for anti-shipping duties as a supplement to the Savoia-Marchetti SM.79 Sparviero torpedo-bombers. It was a regular P.108B but armed with a 90mm high velocity Canone da 90/53 mounted in a redesigned nose. That gun was considered by the time the most successful Italian gun and it was being used both as anti-air and anti-tank by the Army and the Navy. To make it more effective, its size was increased from the standard 90mm (3.5in) to 102mm (4in) which used non-standard Italian artillery calibre and fired heavier shells with a muzzle velocity of 600 m/s (1970ft/s). The gun, together with the recoil system, wighed 1500kg (3300lb) and, thanks that it was a re-bored smaller gun its weight was relatively low for its calibre.
The P.108A concept was in line with other contemporary developments like the North American B-25 Mitchell or the German Henschel Hs.129 both of them having a high-velocity gun mounted in their nose.
The gun was mounted longitudinally at the fuselage centreline, at a depressed angle, and had a powerful recoil which could be absorbed by the fuselage. It could carry 50-60 rounds for the main gun plus three torpedoes plus the defensive armament of two remotelly-controlled turrets mounted on the engines with two 12.7mm (0.5in) Breda-SAFAT machine guns and controlled from the fuselage, plus a retractable ventral one with another Breda-SAFAT and two co-axial 7.7mm Breda-SAFAT machine guns placed close to the doors.
The 102mm gun was intended to be fitted with a ballistic sight, with an analogue computer and a six or 12 round mechanical loader.
The initial prototype, modified from a regular P.108B, flew for the first time on 16th December 1942 in Savona, Italy, and by February 1943, modifications were completed so testing began on 3rd March. Initials tests were satisfactory; it achieved a maximum speed of 440km/h (270mph) thanks to the aerodynamical redesign of the nose. It flew to Furbara in March and later, in April to Pisa where it was tested on firing trials at altitudes between 1500 and 4500m (4900 and 14800ft) in order to collect firing data needed to allow the computing gunsight to be produced. After 24 hours and 40 minutes of flight trials, it was flown back to Albenga and later, on 22nd May 1943 it was officialy presented as the new anti-shipping aircraft at Furbara. It was planned to build five more of them as well as converting many of the existing P.108Bs. However, on 29th June it was decided to limit the number to five of them and in July it was limited to two and eventually, cancelled.
Later, on 6th and 8th September 1943 it made further weapon tests over the sea, equipped with the S.Giorgio computing system. However, after the Italian armistice, German forces took over the prototype and painted their insignias over the Italian ones but it was damaged during an Allied air raid. It was repaired and sent to Rechlin, in Germany, on 7th April 1944 where most probably was destroyed in another air raid.
Even if the P.108A proved to capable, with more than 280 shells fired during tests, the Italian armistice and the change of priorities, halted its development. Initially the use of such large aircrafts in anti-shipping role was questioned, even if the Americans had already used B-17s to bomb Japanese ships at close range and sea level, but with an average speed of 360km/h (220mph), the cost was greater than standard bombers, and the improved anti-air naval defenses like the Bofors 40mm gun, led Germany to develop anti-shipping missiles like the Henschel Hs.293 and the Fritz X.

Sources:
1. https://en.wikipedia.org/wiki/Piaggio_P.108#P.108A
2. La Bancarella Aeronautica - Ali d'Italia 15 - Piaggio P.108