Although it never saw military service, the Knuckleduster provided useful information on the steam-cooling of engines and the handling of monoplane flying-boats; much experimental data gathered contributed to the design of the successful Empire and Short Sunderland aircraft.

[2] The British Air Ministry issued its Specification R.24/31 for a "General Purpose Open Sea Patrol Flying Boat" in 1931 and ordered one prototype from each of Saunders-Roe, Supermarine and Shorts.

[3] The wing sections inboard of the engines were attached at a 30° dihedral angle, thus providing sufficient clearance for the airscrews from water-spray during takeoff.

The engines, with conspicuous condensers protruding vertically from the nacelles, were mounted at the "knuckle" between the dihedral inner and the horizontal outer wing sections.

On 12 June 1934, at the conclusion of test flying, the Knuckleduster was flown to Felixstowe for official trials with the Marine Aircraft Experimental Establishment (MAEE).

In April the Knuckleduster joined 209 Squadron at RAF Mount Batten, Plymouth for service trials alongside the Stranraer and London.

[2] Although it was not ordered into production - mainly hindered by the unreliable engines - a new Air Ministry Specification R.2/33 was released before it flew, which would lead to the Short Sunderland.