The Piaggio P.108 Bombardiere was an Italian four-engine heavy bomber that saw service with the Regia Aeronautica during World War II.

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.

[3] The P.108 was unique in the history of Italian aviation, as it was the only four-engine strategic bomber used by the Regia Aeronautica during World War II.

[6] It performed extremely well in a series of tests and required refining in only a few minor areas, but it took some time for pilots to get used to the new aircraft.

The P.108's tail was even larger, because of the need to stabilise the heavy, powerful aircraft (30,000 kg/66,000 lb and up to 4,500 kW/6,000 hp at take-off, around 20% heavier than early B-17s).

Fiat was a much larger company that also designed and manufactured airframes and powerplants, but limited its production to aircraft like the BR.20 Cicogna, a conventional medium bomber.

The P.XII was two Piaggio P.X engines in tandem, which were versions of the French Gnome-Rhône 9K Mistral made under license, themselves being derived from the license-built Bristol Jupiters.

Alfa Romeo also lacked a powerful, modern engine, and its 1,010 kW (1,350 hp) AR.132s were two Bristol Mercurys in tandem.

This was due to their installed turbochargers, as well as doctrinal differences in high altitude precision bombing advocated by the United States Army Air Forces.

[8] Although considered a very advanced design, the operational suitability of the wing nacelle turret installations was questionable:[9] In response to a request in November 1942, the P.108A Artigliere "gunship" was developed for anti-shipping duties to supplement torpedo bombers.

This was considered the most effective artillery piece in service, and in several versions was used as an anti-aircraft and anti-tank gun by the Army and the Navy.

The P.108A concept was in line with other contemporary developments, as medium bombers such as the North American B-25 Mitchell and even smaller attack-aircraft like the Henschel Hs 129 were being fitted with high-velocity 75 mm (3 in) guns.

The gun was mounted longitudinally in the fuselage centreline, at a depressed angle, and had a powerful recoil, which the 27 tonne (30 ton) airframe was able to absorb.

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.

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 that was required to allow the computing gunsight to be produced.

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.

At sea level, speeds 360 km/h (220 mph) was the best safely achievable, the cost was even greater than that of standard bombers, and the improved naval anti-aircraft defences (Bofors 40 mm guns, P-F shells, and fire-control radar) led Germany to develop glide bombs like the Henschel Hs 293 and Fritz X.

While the P.108B's troubled development continued, Piaggio's workload was further stressed by the request for new transport aircraft, capable of long-range flights to South America for Linee Aeree Transcontinentali Italiane (LATI).

The intention in 1939 to license-build the Boeing 307 Stratoliner wasn't realised, so in 1940, it was proposed to use the P.108C as an "interim" transport, awaiting the P.126C and even the P.127C six-engined variant.

Transportfliegerstaffel 5 operated most of these aircraft and used them until the end of the war, with one assigned to the links between Italy and Germany and the other on the Eastern front.

The final development of the P.108, the P.133 prototype, was almost complete by the time of the Armistice (8 September 1943), but the program was dropped soon afterwards and the aircraft was never finished.

[14] P.108Bs were deployed in the Mediterranean and North African theatres and first saw action in an unsuccessful day mission against a destroyer on 6 June, releasing 10 160 kg (350 lb) bombs.

For a chronology, there were sorties to Gibraltar (without the endurance problems that dogged the first mission), during the night of 3 July (MM.22601 failed to return), 24 September (MM22004 and 22603), 20 October (MM.22002 (written off during an emergency landing after engine failure on takeoff), MM.22004, 22006 and 22007) and 21 October (MM.22602, destroyed during an emergency landing at Bône in Algeria, and two other P.108s), when the "peak" was reached.

Despite limited results, as expected from so few aircraft which included the destruction of a Hudson and some artillery positions on the ground and further unspecified damage, the strategic objective of forcing the Allies to concentrate resources to defend this British exclave had been met, in the same way that only four S.82s had forced the British to allocate defenses and resources to defend the oil refineries at Manama in the Persian Gulf during the Bombing of Bahrain in 1940.

Following the Allied invasion of French North Africa, codenamed "Operation Torch", more losses were sustained when these aircraft flew missions over Algeria and other African targets.

Losses included two aircraft destroyed and two others badly damaged, mainly by Beaufighter and Mosquito night fighters.

P.108Bs ended their activities with a total of about 15 missions over Gibraltar, 28 over North Africa, 12 over Sicily and some other reconnaissance and anti-shipping sorties (of which only one is known).

This aircraft was too complex and difficult to develop without support from the Air ministry and other larger concerns, such as Fiat.

None was forthcoming, and while Piaggio was still struggling to fine-tune and produce the P.108B, there were many other requests for the 'C' model airliner, the P.108T military transport, and the 'A' anti-ship versions.

Production totals of the P108C and T are unclear, but combined there were approximately 16 built, with most of the P108Cs subsequently converted to the transport version.