The P-51 Mustang fighter evolved from a British need for more P-40 Warhawk fighters. North American's Lee Atwood convinced the British that his company could build a better fighter. As a result, the NA-73X prototype Mustang was built in 177 days and first flew Oct. 26, 1940. The first of the production aircraft reached England in April 1941. Their primary mission was to escort bombers deep into Germany, where their efficient aerodynamics allowed them to outclimb the Focke-Wulfs and the Messerschmitts. The Mustang fighters were the first to be used in ground attack operations over occupied Europe.