February 1939 to relocate the aircraft for further testing. General Henry "Hap" Arnold, commander of the USAAC, approved of the record attempt and recommended a cross-country flight to New York. The flight set a speed record by flying from California to New York in seven hours and two minutes, not counting two refueling stops. Kelsey flew conservatively for most of the way, working the engines gently, even throttling back during descent to remove the associated speed advantage. Bundled up against the cold, Arnold congratulated Kelsey at Wright Field during his final refueling stop, and said, "don't spare the horses" on the next leg. After climbing out of Wright Field and reaching altitude, Kelsey pushed the XP-38 to . Nearing his destination, Kelsey was ordered by Mitchel Field tower ( Hempstead, New York) into a slow landing pattern behind other aircraft. Carburetor icing caused it to be brought down short of the Mitchel runway, and it was wrecked. However, on the basis of the record flight, the Air Corps ordered 13 YP-38s on 27 April 1939 for US$134,284 each. (The "Y" in "YP" was the USAAC's designation for service test, i.e. small numbers of early production aircraft, while the "X" in "XP" was for experimental.) Lockheed's chief test pilot, Tony LeVier, angrily characterized the accident as an unnecessary publicity stunt, but according to Kelsey, the loss of the prototype, rather than hampering the program, sped the process by cutting short the initial test series. The success of the aircraft design contributed to Kelsey's promotion to captain in May 1939. Manufacture of YP-38s fell behind schedule, at least partly because of changes to meet the need for mass production, making them substantially different in construction from the prototype. Another factor was the sudden required expansion of Lockheed's facility in Burbank, taking it from a specialized civilian firm dealing with small orders to a large government defense contractor making Venturas, Harpoons, Lodestars, and Hudsons, and designing the Constellation for TWA. The first YP-38 was not completed until September 1940, with its maiden flight on 17 September. The 13th and final YP-38 was delivered to the USAAC in June 1941; 12 aircraft were retained for flight testing and one for destructive stress testing. The YPs were substantially redesigned and differed greatly in detail from the hand-built XP-38. They were lighter and included changes in engine fit. The propeller rotation was reversed, with the blades