 The full scale aircraft was estimated to have a maximum speed of 1,095 km/h (680 mph), but the initial converted Mamba, the SM-1, which was test-flown under a de Havilland Mosquito in 1948 and was the first turbofan to fly, did not generate adequate thrust.Considerable further work was required for the definitive two-shaft SM-5 engine, which was meant to generate 14.7 kN (3,300 lbf) thrust.The prototype was completed in 1952 and, fitted with four SM-1 engines, flew briefly during a taxi test on 8 April 1952 but development of the engine and the N-20 aircraft was cancelled soon afterwards.