The first prototype rolled out of Filton in mid-1938. Problems immediately arose with the Taurus engines continually overheating during ground testing. New, more conventional engine cowlings, with circumferential cooling gills, had to be designed and installed, delaying the first flight, which took place on 15 October 1938. As flight testing progressed, it was found that the large apron-type undercarriage doors, similar to those on the Blenheim, were causing the aircraft to yaw on landing. These doors were taken off for subsequent flights. On the second prototype and all production aircraft, more conventional split doors, which left a small part of the tyres exposed when retracted, were used.