Vought F6U-1 Pirate
The F6U Pirate was Vought's failed attempt to get into the jet fighter market for the US Navy. Vought received a contract for 3 prototypes in 1944. The first prototype flew two years later. It was severely under-powered, so the third prototype was fitted with an afterburning engine.
It was ugly, still under-powered, and unstable, but the first production machines rolled out in 1949.
Performance was so bad that only 30 of the contracted 65 machines were produced, and never saw service with line units.