The Supermarine Spitfire is the most famous British aircraft of World War II. Over 20,000 were built, with over 20 variants. It is also the only British fighter to be manufactured continuously for the duration of the war. The Spitfire, built by Supermarine Aviation Works, was designed as a short-range interceptor aircraft by chief designer R. J. Mitchell. After several setbacks the resulting prototype (K5054), had the graceful flowing lines and semi-elliptical wings of later Spitfires and was powered by the newly developed Rolls Royce V12 engine, later known as the “Merlin.” The prototype was also one of the first aircraft to have retractable landing gear. After brief testing, an order for 310 Spitfires was placed by the Air Ministry. Once the many manufacturing difficulties were overcome, Mk I Spitfire deliveries to the RAF (Royal Air Force) began. Spitfires first distinguished themselves during the Battle of Britain by countering bomber escorts such as the Bf 109’s, while the more numerous Hawker Hurricanes attacked the bombers. Throughout the war the Spitfire had continuous upgrades to its wings, fuselage, armament and especially, engines—from just over 1,000 hp in the early models, to over 2,300 hp by war’s end. The versatile Spitfire was also adapted to specific roles such as high-altitude Interceptor, Fighter-Bomber, Photo Reconnaissance, and even carrier-based fighter (Seafire).