Based on Grumman's earlier F9F Panther, the Cougar replaced the Panther's straight wing with a more modern swept wing and the thrust was also increased. The aircraft was still subsonic, but performance improved markedly over the Panther. Instead of using conventional ailerons for roll control, the Cougar used spoilers on the upper surfaces of the wing. Wing fences were soon added and the spoilers extended from the fences to the tips of the wing.