The Republic P-47 was the successor to a line of airplanes derived from the Seversky P-35, the XP-41, P-43 Lancer and XP-44 Rocket. The P-47 design team headed by Kartveli originally presented a design that was to be powered by a 1,150 hp Allison V-1710-39 engine with an armament of only two 0.50 inch machine guns. A contract was awarded by the USAAC in November 1939, and for an even lighter XP-47A, but as intelligence was coming back from the war in Europe, it was becoming apparent that the performance goals of the XP-47 program were already inadequate. The USAAC issued new requirements which included: