The M.6 Hawcon was a one-off experimental monoplane designed for thick-wing research by the Royal Aircraft Establishment.
The Hawcon combined parts from both the Hawk and Falcon and was powered by a 200 hp (149 kW) de Havilland Gipsy Six piston engine.
The aim was to investigate the performance penalties of thicker wings, which had structural advantages (lower weight for the same strength) and provided space for fuel etc.
The trials showed that the thickness had little effect on maximum speed: wing B was faster than A by 5 m.p.h.
[1] For comparison, modern low Mach number aircraft have root thickness to chord ratios of 0.14 - 0.20.