Flown on 5 March 1936, the prototype was a sleek, stressed-skin machine, with underwing radiators and outwards-retracting landing gear.  The characteristic elliptical wing was based on a strong leading edge and a single spar made of a stack of square tubes one inside the other, tapering to a channel and then to a plain angle towards the tip.

Its handling qualities were almost perfect, almost the only problem being that, as speed increased, rate of roll was reduced until at 400mph the ailerons felt almost immovable.  This was a common fault, and the Spitfire's greatest adversary, the Bf 109, was even worse.  Lookout Focke-Wulf pilots...

Spitfire production totaled 20,334 plus 2,550 carrier-based Seafires.  The final versions were more than twice as heavy and twice as powerful as the prototype, and over 100mph faster.