06/30/2011. Remarks by Johan Visschedijk: "As flown in 1928, the first Gnatsnapper (above) had a 540 hp Armstrong Siddeley Jupiter VII nine-cylinder air-cooled radial engine, two side-mounted synchronized Vickers 0.303 in (7.7 mm) machineguns, and plain ailerons. The Gnatsnapper was designed to the requirements of Specification N.21/26 calling for a single-seat shipboard fighter of all-metal construction and powered by a 450 hp Bristol Mercury IIA nine-cylinder air-cooled radial.
The first of two prototypes, temporarily powered by a Jupiter VII engine, flew in February 1928. The Mercury IIA was subsequently installed, but as this did not measure up to anticipated performance or reliability, the Jupiter VII was reinstated for official trials. The second prototype, serialed N254, was not completed until March 1930, initially with a Mercury IIA, but the designated power plant was again discarded shortly thereafter.
The first prototype was re-engined with a 540 hp Armstrong Siddeley Jaguar VIII fourteen-cylinder air-cooled radial as the Gnatsnapper II, but suffered damage during official trials. In 1931, it was re-engined once more, with a steam-cooled 525 hp Rolls-Royce Kestrel IIS, as the Gnatsnapper III, subsequently serving as a Rolls-Royce test-bed and hack aircraft."