[1][2] In November 1916, a requirement for a single-engined, single-seat bomber was issued on behalf of the RNAS,[3] and when Sunbeam decided to design an aircraft to respond to this specification, it received an order for two prototypes from the Admiralty.
Racks for three 100 lb (45 kg) bombs were fitted under the wings, while a single forward-firing synchronized Vickers machine gun was mounted above the aircraft's engine.
The Puma engine, despite being ordered in large numbers, was unreliable and suffered from severe vibration, which considerably delayed service testing.
When eventually formally tested, in August 1918, it proved to be heavier and carry fewer bombs than the private venture Sopwith B.1 of similar concept.
[4] The second prototype was abandoned before it was completed, and no orders were placed either for the Sunbeam or the Sopwith,[5] which were incapable of defending themselves against attacking enemy fighters[6] Existing two-seat aircraft such as the Airco DH.4 better met the RNAS's (and later the Royal Air Force's) requirements.