The P-38 was the only American fighter built before World War II to be still in production on V-J Day. Developed through many successively improved versions, the Lightning was used in all US combat zones as a high- and low-altitude fighter, fighter escort, bomber, photographic-reconnaissance aircraft, low-level attack and rocket fighter, and smoke-screen layer. The first aircraft developed from the start as a military type by Lockheed, the P-38 was designed to meet an Air Corps specification issued in 1936. The XP-38 prototype flew for the first time on 27 January 1939 and the first YP-38 service-evaluation aircraft was delivered to the USAAF in March 1941. The P-38L was the last fighter version to see combat service, which took in the final stages of the Pacific War. A total of 10'000 were built.