Martin-Baker MB 3

The Martin-Baker MB3 was a British fighter project that was designed by James Martin and Captain Valentine Baker using the experience learned from the previous MB1 and MB2. It was powered by a 2000hp Napier Sabre engine with a variable pitch three bladed propeller.
It was designed to meet one of the Air Ministry's specifications and was armed with six 20mm (0.79in) cannons in the wings, three per each wing, making it one of the most armed fighters of the World War II if it had been produced and, following Martin-Baker's tradition, they were easily accessible and maintaineable. Retaining the characteristics of the previous designs, it introduced many new features, as the fuselage was still made in round steel tube but metal place replaced the wood and fabric on earlier models. The wing construction integrated torsion-box construction and a laminated steel spar, giving it that way a strong and stiff structure with minimum flexing. It had also a very effective, simple, sturdy and reliable pneumatically-controlled undercarriage.
It was tested and flew for the first time on 31st August 1942, and it revealed to be highly maneouvrable and easy to handle, however, on 12th September, the engine failed soon after taking off and it crashed unfortunately killing the pilot, Captain Valentine Baker. This leaded to various delays and late deliveries, making the project uninteresting for the Air Ministry.
There were, however, plans to redesign it as an Mk.II version with a bubble canopy and powered by either a Napier Sabre, or a Rolls-Royce Vulture engine. Those versions apparently weren't the MB4 but some developed variants of the MB3. Trully a good looking fighter.

Sources:
1. https://en.wikipedia.org/wiki/Martin-Baker_MB_3
2. https://www.secretprojects.co.uk/forum/index.php?topic=7053.0
3. Salamander Books - The Complete Book of Fighters