The Savoia-Marchetti S.55 was a double-hulled monoplane flying boat designed and produced by the Italian aircraft manufacturer Savoia-Marchetti. It was designed to perform both commercial and military applications. The S.55 featured numerous innovative design features. While the passengers and cargo were housed within the twin hulls, the flight crew controlled the aircraft from a cockpit located in the thicker section of the wing between the two hulls. The S.55 had two inline contra-rotating propellers, mounted in tandem. The engines were canted sharply at an upward angle. Two wire-braced booms connected the triple-finned tail structure to the twin hulls and wing. During August 1924, the S.55 performed its maiden flight. Shortly after its introduction, the S.55 set multiple records for speed, payload, altitude and range. Numerous flying boats saw service with the Regia Aeronautica and export operators such as the Spanish Air Force and the Royal Romanian Naval Aviation as reconnaissance bombers and maritime patrol aircraft. While some examples were active by the outbreak of the Second World War, the type only played a marginal role in the conflict due to their age.