Martin-Baker also considered designs for a twin-engine 12 gun fighter and a multi seat transport. In the fighter design the trailing edge of the of the engine nacelles provided additional vertical control surfaces and also incorporated a patented ducting system evolved by Martin-Baker to reduce drag caused by the exhaust.
The decision of the Authorities not to go ahead with the development of this design was disappoint-ing and a setback for Martin-Baker and as a grave error of judgement to Senior RAF officers when the country needed new fighters. The MB3 was the Company‘s next bid to meet an Air Ministry requirement for a fighter. All the lessons learned from the construction of the previous two marks of low mono wing aircraft were embodied.
The aircraft was powered by the Napier Sabre 24-cylinder 2,000hp engine driving a De Havilland variable-pitch three bladed propeller. It carried six 20 mm cannon each with 200 rounds which made it the most heavily armed fighter of the time. The pneumatically controlled undercarriage was simple, sturdy, effective and reliable. The wing flaps were also pneumatically controlled eliminating hydraulics and all the problems of their maintenance. The radiators were installed underneath the wings with the engine coolant on the starboard and the oil-cooler on the port. The aircraft was highly manoeuvrable and easy to fly. It could have been developed into an excellent fighter however the aircraft was totally destroyed on a test flight when the engine failed and Captain Baker was killed trying to save his aircraft. Time constraints meant that a second aircraft was not built.
So ended the Napier / Martin-Baker alliance.