The prototype flew for the first time on March 5, 1936, although the first Mk I was not delivered to 19 Squadron at RAF Duxford until August 4, 1938. Designed by Reginald Joseph Mitchell, the Spitfire became one of the most successful fighter aircraft ever built. By September 1939, ten Spitfire squadrons were operational, and 19 were ready to engage the Luftwaffe during the Battle of Britain. The Spitfire was championed as the most effective fighter during this period. The RAF flew its last operational Spitfire (PR.Mk XIX) sortie over Malaya, on April 1, 1954, reconnoitring rebel positions.