The Piaggio P.108 was remarkable as it was the only 4-engined bomber to serve with the Regia Aeronautica. Bearing a striking resemblance to the B-17 Flying Fortress, the P.108 was produced in too few quantities to have any significant role in the war despite the fact that it was a remarkably good bomber which was capable of carrying a considerable bomb load and having a long range. It also had fairly heavy defensive armament including some remote-controlled turrets, something not seen until late in the war by more modern designs. The P.108 performed missions in North Africa, Russia, the Balkans and even some spectacular night bombing missions against Gibraltar (one such raid resulted in the death of Benito Mussolini's son, a pilot). It is unfortunate that more potential from this superb aircraft was not seen by Italian authorities in time and as such, heavy losses decimated its numbers by the time of the surrender although some ended up in the Luftwaffe.

The prototype P.108 was finished in October 1939 and entered service as the P.108B which was the main production variant, later modified as the P.108M with additional defensive armament. Other planned versions included the P.108A with a 102-mm anti-shipping gun in the nose, the P.108T and P.108T2 transports, and the P.108C civil transport which could carry up to 32 passengers. After the surrender, the Luftwaffe used the transports extensively most notably during the Crimea evacuation. A further Piaggio development was the P.133 with more powerful engines and a heavier bomb load but was never built.