The Grumman F9F Panther was the manufacturer's first jet fighter and the US Navy's second. It first flew in 1947. Its power source was a Rolls-Royce Nene turbojet built under license by Pratt & Whitney as the J42. Since there was insufficient space within the wings and fuselage for fuel for the thirsty jet, permanently mounted wingtip fuel tanks were added. The F9F-3 was an Allison J33-powered version produced as insurance against the failure of the J42. A total of 54 built, and all were converted to J42 power later.