It was armed with six 20 millimetres (0.79 in) cannon mounted in the wings, each with 200 rounds of ammunition, which made it the most heavily-armed fighter in existence: for ease of maintenance the armament was easily accessible.

[1] Then listed as "Experimental Aeroplane No.120" and with the serial number R2492, the MB 3 was temporarily stationed at 26 OTU (Operational Training Unit) at RAF Wing in Buckinghamshire for trials and first flew on 31 August 1942.

[1] The tests were supervised by Group Captain Snaith and observed by, amongst others, Air Vice Marshals Francis John Linnell (Controller of Research and Development at the Ministry of Aircraft Production) and Burton.

Following its successful first flight, undertaken by Captain Baker, the next series of test flights revealed the MB 3 to be highly manoeuvrable and easy to fly, but on 12 September 1942, the engine failed soon after take-off and Captain Baker, trying to save the aircraft by executing a difficult forced landing, crashed in a field and was killed.

Civilian John Thornton also witnessed the accident, Two fields from where Morris and I were harvesting, there was a stack of newly-threshed straw.

'Bunny' Winter, the bailiff of Cold Harbour Farm, beat us to the crash, but we were too late to rescue Captain Baker in the fierce fire.

Martin felt the personal loss of his best friend and partner and "many consider that it was this painful tragedy that really fired the passionate interest in the safety of aircrews, which was later to become the very pivot of his life".