The AD Flying Boat was designed by the British Admiralty's Air Department to serve as a patrol aircraft that could operate in conjunction with Royal Navy warships. Intended for use during World War I, production of the aircraft was terminated as the end of the war came into sight, and the type saw little operational use. A number were re-purchased after the end of the War by Supermarine Aviation and rebuilt as civil Transports, becoming known as the Supermarine Channel.
Designed in 1915 by Lieutenant Linton Hope, the aircraft was of conventional biplaneflying-boat configuration, and also featured a biplane tail with twin rudders. The pilot and observer sat in tandem in the nose, with the engine and pusher propeller mounted behind them, between the wings. The wings could be folded forwards to facilitate shipboard stowage.
Two prototypes were constructed in 1916 by Pemberton-Billing Ltd (later to become Supermarine Aviation). The first prototype was intended to be powered by a 150 hp (112 kW) Sunbeam Nubian engine, but this was not ready with the Hispano-Suiza 8 being substituted. Handling, both on the water and in the air was initially poor, demonstrating severe fore and aft vibration, known as porpoising during take-off, while subject to excessive Yaw during flight. These problems were eventually solved by revisions to the hull and the fin and rudder, allowing the AD Flying Boat to be ordered into production. A total of twenty-seven production machines were built out of orders for eighty, generally powered by 200 hp (149 kW) Hispano-Suiza engines, although examples were tested with Sunbeam Arab and Wolseley Python engines.
Following the Armistice, Supermarine purchased nineteen of these aircraft back to modify them for the civil market as the Supermarine Channel, either as the Channel Mk I with 160 hp (119 kW) Beardmore 160 hp engines, or the Channel Mk II powered with 240 hp (179 kW) Armstrong Siddeley Puma engines. The reconfigured flying-boats provided accommodation for a pilot and three passengers in three open cockpits.