This is XF-91 46-680 marked as XF-91 46-681. It is unknown why the USAF Museum had the wrong serial number on the a/c. 46-680 was delivered to the museum in 1955. When displayed later at the new museum it had the correct s/n on the vertical fin. This slide was taken at the outdoor aircraft display area at the old museum on Patterson AFB. It is still part of the museum collection but as of 2022 it is in storage according to the museum website.

The first of two prototype XF-91 single-seat supersonic interceptors powered by a J47 and a 6000 lbs XLR11 rocket. First flew 9 May 1949. No serial production of the type was undertaken.

While developing the XP-84, Republic looked at installing rockets in fighters, inspired by late wartime German research. However the resulting XP-91 was quickly obsolete thanks to the rapidly increasing performance of newer jet engines and only two prototypes were built, although one was the first US fighter to exceed Mach 1 in level flight. An unusual feature was the wing planform, markedly tapered outwards from the fuselage to a wide chord at the wingtips to combat stall problems with early swept-wing designs