The W91 was an American thermonuclear warhead intended for use on the SRAM-T variant of the AGM-131 SRAM II air to ground missile. What was to become the W91 design entered into a Phase 2 design competition between the various nuclear weapons laboratories in November 1988. Further development details are somewhat unclear, but a Los Alamos National Laboratory design won the competition. The design was cancelled in September 1991 along with the SRAM T missile, prior to production of any units, though some test devices may have been manufactured.