How much did the Air Corps pay for the XP-38 prototype, and how much did it cost Lockheed?

The P-38 originated from a February 1937 specification by the US Army Air Corps (USAAC), Circular Proposal X-608. Lockheed won the competition on 23 June 1937 with its Model 22 and secured the contract to build a prototype, the XP-38, for $163,000. Lockheed's own costs on that prototype totaled $761,000. Construction began in July 1938 in a former bourbon distillery that Lockheed had bought to house its growing activity.

The XP-38 first flew on 27 January 1939, piloted by Ben Kelsey. Following its record-setting flight, the Air Corps ordered thirteen YP-38 on 27 April 1939 at $134,284 each. The YP-38 were thoroughly redesigned and differed greatly in detail from the hand-built XP-38, partly due to the changes needed for series production. The first was not ready until September 1940 and flew on the 17th of that month; the thirteenth and last was delivered in June 1941.

On 20 September 1939, before the YP-38 were built and tested, the Air Corps ordered 66 initial production P-38. The aircraft would go on to be the only American fighter mass-produced throughout the United States' entire involvement in the war, and its most numerous variant, the P-38L, reached 3,923 units.

The prototype was also a technical breakthrough: the P-38 was the first American fighter to make extensive use of stainless steel and flush-riveted smooth aluminum panels, and the first military aircraft to exceed 400 mph (640 km/h) in level flight. Of the thirteen YP-38, twelve were used for flight testing and one for static tests to destruction.