W59

American thermonuclear missile warhead

The W59 was an American thermonuclear warhead used on some Minuteman I ICBM missiles from 1962 to 1969, and planned to be used on the cancelled GAM 87 Skybolt air launched ballistic missile.

Development of the Minuteman I ICBM was authorized in February 1958 and by March, the study of possible warhead for the new ICBM was completed. In April, the XW 56 warhead designed by Lawrence Radiation Laboratory (now Lawrence Livermore National Laboratory) was approved for development. This program required considerable effort and was accompanied by funding issues. Though the intermediate details and dates remain classified, at some point during or before December 1960, a second Minuteman warhead was authorized with a planned first production date of July 1962 and a full scale production date of December 1962. In March 1961, the XW 59 nomenclature was accepted for this warhead. Firing set components would be off the shelf items repackaged for the special shape required for the role. The warhead would contain no electrical power, with an externally powered rotary chopper provided to charge the weapon's X unit. An inertial switch would be provided to prevent weapon arming before it experienced its launch environment. In December 1960, it was decided to use the environmental sensing device (ESD) from the XW 56 in the XW 59. In January 1961, the Mark 5 reentry vehicle (RV) joint working group, already assigned the task of mating the XW 56 to the Mark 5 were also given the task of fitting the XW 59 to the RV. In May, a second working group for the Mark 11 RV was formed. The plan was to introduce the Mark 11 into service in January 1963 with the eventual replacement of all Mark 5 RVs with Mark 11s. In May 1961 it was noted that the weapon's RV and fuzing system would be developed by Avco while Sandia National Laboratories would be responsible for the firing set, external initiators, ESD and housing and mounting structures. The warhead would also be compatible with the Skybolt application and that all electrical components, except the external initiators, were already in production. Safety was assured by not having any source of power in the warhead, the use of ESDs, and that two firing signals in the correct order had to be received to detonate the weapon. Flight tests of the weapon were conducted in late 1961 and the Mark 59 Mod 0 warhead was design released in December 1961. Though the Minuteman missile's operational availability date was pushed from July to September 1962, the warhead's first production date remained unchanged and the first warhead was delivered on schedule in June 1962. The final development report for the Mark 59 Mod 0 noted that the warhead met all the design specification, with some still classified exceptions. A total of 150 W59 warheads were produced from June 1962 to July 1963. All warheads were retired by June 1969. From official documents, it had a design yield of efn|The report states that the warhead for Minuteman has a yield of and the warhead had a yield of The W59 is the only 550lb warhead for Minuteman. Historical evidence indicates that these weapons shared a reliability problem, which Hansen attributes to miscalculation of the reaction cross section of tritium in fusion reactions. The weapons were not tested as extensively as some prior models due to the 1958 to 1961 test moratorium, and the reliability problem was discovered and fixed after the moratorium ended. This problem was apparently shared by the Python primary designs.