At the beginning of World War II, Lockheed – under the guidance of Clarence (Kelly) Johnson, who is considered one of the best-known American aircraft designers – answered a specification for an interceptor by submitting the P-38 Lightning fighter aircraft, a twin-engined, twin-boom design. The P-38 was the only American fighter aircraft in production throughout American involvement in the war, from Pearl Harbor to Victory over Japan Day. It filled ground-attack, air-to-air, and even strategic bombing roles in all theaters of the war in which the United States operated. The P-38 was responsible for shooting down more Japanese aircraft than any other U.S. Army Air Forces type during the war; it is particularly famous for being the aircraft type that shot down Japanese Admiral Isoroku Yamamoto's airplane.