A prototype (military serial L7999) with 1,060 hp Bristol Taurus T-S(a) radial engines flew on 3 April 1939 and demonstrated excellent performance, its maximum speed of  being the best recorded by a British fighter at the time. Test flights revealed that the prototype was very manoeuvrable and "a delight to fly".
A test aircraft (military serial L7999) powered by 1,060 hp Bristol Taurus T-S(a) radial engines made its first flight on 3 April 1939 and exceeded expectations with its outstanding performance, achieving the highest recorded speed for a British fighter at that time. Flight evaluations showed that the prototype was highly responsive and "a joy to fly".