[ U.S. Air Force Photograph. ] black-and-white photos XP-51 January 5, 2013by Lone_Sentry_Admin1 min read The North American XP-51 (S/N 41-039), a design which would eventually become the famous P-51 Mustang. Pictured is the 2nd aircraft built. (U.S. Air Force Photograph.) ( U.S. Air Force Photograph. )