In November 1943 the company was ordered to build a dual-control dive-bombing trainer variant against Specification T.21/43 and this was built at the Heaton Chapel factory and assembled and flown at Ringway on 20 June 1946.

The second prototype was used by the Royal Navy Carrier Trials Unit at RNAS Ford, Sussex, until it was sold for scrap on 15 September.

The third prototype conducted ASV Mk.XV radar trials, but was damaged in a heavy landing on 1 September 1949 and sold for scrap on 22 August 1950 as uneconomical to repair.

The sole Heaton Chapel-built aircraft was the closest to the planned production configuration and it was used for engine-cooling and power-assisted flying-control trials, until it was struck off charge on 24 July 1951.

[10] In a follow-up, to meet Specification O.21/44 for a two-seat strike fighter, the Spearfish was redesigned to accommodate a twin-coupled Rolls-Royce Merlin engine and contra-rotating propellers.

A variety of other engines were considered and although a production order was placed for three examples in 1944, the programme was eventually shelved, remaining as an unfulfilled paper project.

[12] The large internal weapons bay could alternatively carry up to four 500-pound (230 kg) bombs, four depth charges, a torpedo, or a 180-imperial-gallon (820 L; 220 US gal) auxiliary fuel tank.

The Spearfish was intended to carry four 0.5-inch (12.7 mm) M2 Browning machine guns, two in a remote-controlled Fraser-Nash FN 95 barbette behind the cockpit and two in the wings.