Designed by RJ Mitchell, who was noted for making fast-flying seaplanes, the first version of the Spitfire was introduced into RAF service in 1938 and immediately became extremely popular with pilots. Its aerodynamic frame was fitted with a powerful Rolls-Royce Merlin engine – one of the most successful piston engines ever developed. During the Battle of Britain, Spitfires, armed with eight .303 machine guns, intercepted incoming German fighter aircraft.