The Mark 27 nuclear bomb and closely related W27 warhead were two American thermonuclear bomb designs from the late 1950s. History and design The Mark 27 was designed by the University of California Radiation Laboratory (UCRL; now Lawrence Livermore National Laboratory) starting in the mid-1950s. The basic design concept competed with the Los Alamos Scientific Laboratory (LASL; now Los Alamos National Laboratory) design that would become the Mark 28 / B-28 nuclear bomb and W28 warhead. The Mark 27 was roughly twice as heavy as the Mark 28/B-28/W28 family of thermonuclear weapons. The Mark 27/W27 devices had a yield of versus the (later ) of the Mark 28/B-28/W28 weapons. The Mark 27 and W27 were produced from 1958; both were retired by 1964, as the Kennedy administration began to redirect funding from manned nuclear bomber programs. Both US Navy bombers carrying the Mark 27 bomb, the Douglas A-3 Skywarrior and North American A-5 Vigilante, were repurposed from the nuclear strike role to tanker, electronic countermeasure (A-3) or reconnaissance (A-5) roles by 1965. The W27 warhead was in diameter by long, and weighed . 20 W27 warheads were produced for the United States Navy SSM-N-9 Regulus II cruise missiles. The W-27 warhead was withdrawn from service along with the Regulus cruise missile in 1964. The Mark 27 bomb was in diameter by long, depending on specific version. The three versions weighed . 700 Mark 27 bombs were produced. Explanatory notes See also List of nuclear weapons SSM-N-9 Regulus II References External links Allbombs.html list of all US nuclear warheads at nuclearweaponarchive.org Cold War aerial bombs of the United States Nuclear bombs of the United States Military equipment introduced in the 1950s