102mm cannon!

The Piaggio P.108 Bombardiere was an Italian four-engine heavy bomber that saw service with the Regia Aeronautica during World War II.[3] The prototype first flew on 24 November 1939 and it entered service in 1941.[3] It was one of a handful of Italian combat aircraft that could match the best manufactured by the Allies.[4] Four versions of the P.108 were designed, but only one, the P.108B bomber, was produced in any quantity before the armistice. The other variants included the P.108A anti-ship aircraft with a 102 mm (4 in) gun, the P.108C, an airliner with an extended wingspan and re-modelled fuselage capable of carrying 32 passengers, and the P.108T transport version designed specifically for military use. Only one P.108A and 24 P.108Bs were built. The combined total number of all versions (and prototypes) was at least 39, almost certainly more than 44.[3] Most of the P.108Cs were subsequently modified for use as military transport aircraft and could accommodate up to sixty passengers.[5] Nine P.108 Ts were used by Luftwaffe transport units until the end of the war.[3]

The 102mm variant:

The Piaggio P.108A Artgliere (lit. "Gunship") was an unusual variant of the P.108 heavy bomber. Designed in response to a requirement issued in November 1942 to supplement torpedo bombers in anti-shipping duties, the P.108A was armed with a massive 102 mm 102/35 mod.14 cannon (a bored-out version of the proven 90 mm 90/53 mod.41 anti-tank cannon) in its fuselage, one of the largest armaments ever fitted onto an aircraft at that time. To maximize the effectiveness of the gun, the plane was to be fitted with an analog computer to help in calculating the aim, as well as a 12-round autoloader. However, due to the worsened situation of Italy, frequent Allied bombing raids, and the realization that such an aircraft was more expensive than a traditional bomber while its theoretical effectiveness was questionable at best, only one prototype was built and tested before the program was cancelled in September 1943. The sole P.108A would later be captured by the Germans but presumably destroyed in a later bombing raid in 1944.