 One aircraft ("EW998") was passed to the British who gave it the name Mustang Mk I (Dive Bomber).In April 1942, the RAF's Air Fighting Development Unit (AFDU) tested the Mustang and found its performance inadequate at higher altitudes.As such, it was to be used to replace the P-40 in Army Cooperation Command squadrons, but the commanding officer was so impressed with its maneuverability and low-altitude speeds, he invited Ronnie Harker (from Rolls-Royce's Flight Test establishment) to fly it.