The Piaggio P.108 was the only four-engine heavy bomber used by the Regia Aeronautica during World War II.
In 1938 the Regia Aeronautica issued a request for proposal for a BGR (Bombardiere a Grande Raggio, long-range bomber); proposals came from Caproni with their Ca.204 and Ca.211 projects, CRDA with Cant. Z.1014 (built only in mock-up form), Piaggio with the P.108B (a private venture project, offered as an additional entry) and the P.112. Also considered was the purchasing of a production license for the Boeing B-17C 'Fortress', but this idea was later discarded for reasons of autarchia (national self-sufficiency). The competition was won by the Cant. Z.1014, but since the development of the P.108B was already at an advanced stage, this aircraft was chosen to be produced in quantity.
The Piaggio P.108 was a development of the earlier underpowered and wooden-structured P.50-II (above) which was unable to take-off at its designed maximum weight.
Giovanni Casiraghi, an experienced engineer who had previously worked in the USA for several years, re-engineered the aircraft, giving it a metallic structure. Still not entirely satisfied, he started another, almost new project, the P.108, and initial developments resulted in the P.108B (Bombardiere).
The first prototype P.108B flew on 24 November 1939. The "teething problems" of the P.108 involved a very long period of debugging, and the process of improving its reliability was never totally successful. The first machines were sent to 274 Squadron (274ma Squadriglia) in 1941.
On 7 August 1941, Bruno Mussolini, the son of Italian dictator Benito Mussolini and commander of 274 squadron, was piloting one of the prototypes of the "secret" bomber.
He flew too low and crashed into a house. The cockpit section separated from the rest of the aircraft and although the aircraft did not catch fire, it was nevertheless totally destroyed in the impact. Bruno Mussolini died of his injuries.
By the end of 1941, the P.108B had flown just 391 flying hours which does not compare favorably with the 9,293 hours flown by the first 12 B-17s. Nonetheless, the new bomber showed much promise. The average Italian bomber cost around 2.1 million lire, the SM.79 cost 1.7 million lire, while the P.108 cost 5.2 million lire.
With a single squadron of nine P.108s capable of flying 1,100 km (700 mi) with 3,500 kg (7,700 lb), the estimated efficiency was comparable to a group of 26 SM.79s covering 1,000 km (620 mi) with 1,000 kg (2,200 lb). The total cost of the aircraft was 46.8 and 45.6 million lire respectively, but only 54 crew were required to man the P.108s compared to 130 required to man the SM.79s.
The variants, built only as prototypes or in small numbers, comprised first the single P.108A Artiglieri anti-shipping aircraft (above) which, converted from the P.108 prototype, had its standard armament supplemented by the installation of a 102-mm cannon. Captured by German forces at the time of the Allied-Italian armistice, it was impressed for service with the Luftwaffe. The P.108C Civile was a civil transport version with increased wing span and a redesigned fuselage to accommodate 32 passengers. A total of 16 was built, including one prototype, but these were modified for use as military transports accommodating 56 troops, and about 24 P.108Bs were also converted to this configuration. One P.108T (Trasporto) military transport prototype was built as a conversion from a P.108C, from which it differed primarily by incorporating side loading doors and a ventral hatch.
Proposed variants included the P.108M (Modificato), a development of the P.108B with the single machine-gun in the nose turret replaced by four guns and a 20-mm cannon; and the P.133 (above), an advanced version of the P.108B with uprated engines and an increased bomb load.
The P.108B's engines were designed to be more powerful than those propelling the B-17, and most of its defensive gun turrets were remote-controlled, but its reliability fell short of the typical Allied heavy bombers, and this type remained relatively unknown until the 1970s.
The second series, designated P.108B II, were a revised sub-category having had the nose turret removed. While this reduced defence against head-on attacks, the aircraft was operated mainly at night. The speed gain was 10 km/h (6 mph), due to the weight reduction and the more aerodynamic nose.
They were hardly used by the Regia Aeronautica, the main user being the German Luftwaffe. In 9/43, after the Italian armistice, the Luftwaffe captured all fifteen P.108 Cs and the only P.108 T built. They were used at the Russian front as part of Luftflotte 2 where they performed sterling service, evacuating encircled German troops. The P-108Cs/T proved to be more reliable than the bombers, following successful efforts to improve and modify them.