The P-322 designation was used for aircraft taken over by the USAAF after the RAF cancelled an order for 667 P-38 Lightnings in 1942. This order had been inherited from the French, and had been for a simplified version of the aircraft, without the turbo-superchargers used by all USAAF P-38s.

Before receiving its first Lightnings, the RAF had changed its order to include 146 Lightning Mk Is, as ordered by the French, and 524 Mk IIs, which would have closely resembled the P-38E. The USAAF took over the British order, and completed the 524 Mk IIs as standard P-38Fs and P-38Gs.

The earlier aircraft was also taken over. Twenty two were completed as ordered, and given the designation P-322-I. The remaining 121 were given "F" series engines, as used in American P-38s, although they still lacked the turbo-supercharger. These aircraft were given the designation P-322-II. In American service these aircraft were used as advanced trainers, providing an ideal way to introduce new pilots to the P-38 without the added complexity of the turbo-supercharger for them to worry about.