In the course of RAF trials, despite the Merlin engine proving to be problematic, having suffered numerous failures and necessitating several changes, enthusiastic reports were produced in the aircraft and its performance figures. The trials had observed the aircraft to possess a maximum level speed of 315 mph at an altitude of 16,200 ft, a time-to-climb to an altitude of 15,000 ft from takeoff of 5.7 minutes, and a stalling speed of 57 mph (only marginally higher than the Gladiator biplane), the last achieved using its flaps.