The Martin-Baker MB 3 was a British fighter project with six 20 mm cannon.
The fatal crash of the sole prototype led to the cancellation of the program.
Using lessons learned from the MB 1 and MB 2, James Martin and Captain Valentine Baker capitalised in developing the design and construction to produce a new design, the MB 3, which was powered by a 2,000 hp Napier Sabre 24-cylinder, H-type engine, driving a de Havilland variable-pitch three-bladed propeller.
The MB 3 was to meet an Air Ministry specification for a fighter.
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.
Three were ordered to specification F.18/39 which was written for the design.
While retaining the essential characteristics of the earlier designs, MB 3 included many new features: the fuselage primary structure was still the round steel tube arrangement, but metal panels had taken the place of wood and fabric of earlier models.
The wing construction integrated torsion-box construction and a laminated steel spar, would give a strong and stiff structure with minimum flexing.
Attention to detail extended to a Martin-designed pneumatically controlled undercarriage that was simple, sturdy, effective and reliable.
With the wing flaps also pneumatically operated, the need for hydraulics, with all their attendant operational hazards and maintenance problems, was eliminated.
Underwing radiators had the coolant radiator on the starboard and the oil cooler on the port side.
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.
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.