In 1944, Kartveli began working on a turbojet-powered replacement for the P-47 Thunderbolt piston-engined fighter. The initial attempts to redesign the P-47 to accommodate a jet engine proved futile due to the large cross-section of the early centrifugal compressor turbojets. Instead, Kartveli and his team designed a brand-new aircraft with a streamlined fuselage largely occupied by an axial compressor turbojet engine and fuel stored in rather thick unswept wings. On September 11, 1944, the United States Army Air Force released General Operational Requirements for a day fighter with a top speed of 600 mph (521 knots, 966 km/h), combat radius of 705 miles (612 nm, 1,135 km), and armament of either six 0.50 inch (12.7 mm) or four 0.60 inch (15.2 mm) machine guns. In addition, the new aircraft had to use the General Electric TG-180 axial turbojet which entered production as the Allison J35.