A twin-fuselage aircraft has two main fuselages. It is distinct from the twin-boom configuration which has a single main fuselage with two subsidiary boom structures. Twin fuselages have been adopted for various reasons, and a few types have entered production.
Early seaplanes
During and after World War I a number of twin-fuselage floatplanes and twin-hulled flying boats were constructed, and several entered production: The Blackburn T.B. of 1915 was a long-range floatplane for anti-Zeppelin patrol. A handful of production examples were delivered but few were used operationally. The British Wight Twin Seaplane of 1916 was a prototype long-range floatplane intended to carry an 18-inch torpedo. Its design was a twin-fuselage variant of the earlier Wight Twin Landplane of twin-boom configuration, i.e. with the central nacelle removed and the crew housed in the remaining bodies on either side. The French Labourdette-Halbronn H.T. 1 and H.T.2 flying boat prototypes of 1918-1919 were intended for a similar role. Savoia-Marchetti produced two twin-hulled flying boat types, the S.55 multirole flying boat of 1924 and the S.66 airliner of 1931, both of which took advantage of a twin hull/fuselage to provide the same stability of a twin float design, but with a hull. The S.55 proved very successful, being produced in large numbers. The Tupolev ANT-22 flying boat prototype conceptually followed the Savoia's, but was much larger and despite flying in 1934 never progressed beyond a single prototype due to poor performance.
During World War II the need arose for a heavy glider tug capable of towing the large Gotha Go 242 and even larger Messerschmitt Me 321 Gigant. The Heinkel He 111ZZwilling was created by joining two He 111 fuselages with a new wing centre section and adding a fifth central engine. Although liked by its pilots when it first flew in 1941, even the 111Z could not tow a fully laden Gigant, and although a small batch became operational they saw little action. A few variants were developed for roles such as long-range reconnaissance or air-launched anti-ship missile carrier, but none entered service.
Heavy fighters
During World War II a need arose for a heavy fighter, which could not be met by a new design proposal in a reasonable time frame. Joining two examples of an existing light fighter aircraft was one way to achieve this. The German Messerschmitt Bf 109Z twin Bf 109 prototype was destroyed in an attack by the British in 1943 before it was completed, and the project subsequently abandoned. The later Me 609 twin Me 309 project was never built. In 1944 Dornier proposed the Dornier Do 635 long-range reconnaissance variant of the Do 335 Pfeil heavy fighter, to have twin Do 335 fuselages and four engines. It was never built. The Italian Savoia-Marchetti SM.92 prototype was unusual in being an adaptation of a twin-boom design but did not enter production. The North American F-82 Twin Mustang arrived too late to enter service during the War but later saw service in the Korean war.
