W59

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.{{Cite report| publisher = Sandia National Labs., Albuquerque, NM (USA)| page = 7| title = History of the Mk 59 Warhead| date = 1968| ref = {{harvid|History of the Mk 59 Warhead}}| url = https://osf.io/7j5qn/| access-date = 2021-11-06| archive-date = 2021-12-01| archive-url = https://web.archive.org/web/20211201014448/https://osf.io/7j5qn/| url-status = live}}

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.{{sfn|History of the Mk 59 Warhead|p=8}} In March 1961, the XW-59 nomenclature was accepted for this warhead.{{sfn|History of the Mk 59 Warhead|p=5}}

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{{Definition needed|date=August 2023}} 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.{{sfn|History of the Mk 59 Warhead|p=8}}

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.{{sfn|History of the Mk 59 Warhead|p=9}}

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.{{sfn|History of the Mk 59 Warhead|p=10}}

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.{{sfn|History of the Mk 59 Warhead|p=13-14}}

The final development report for the Mark 59 Mod 0 noted that the warhead met all the design specification, with some still classified exceptions.{{sfn|History of the Mk 59 Warhead|p=14}}

A total of 150 W59 warheads were produced from June 1962 to July 1963. All warheads were retired by June 1969.

Search for a suitable warhead for the Skybolt missile began in March 1960. The requirements included a first production date of July 1963 and that the weapon could be made in large numbers. In April 1960 a study group met to determine a suitable design compatible with Skybolt.{{sfn|History of the Mk 59 Warhead|p=17-8}} The operational deployment date was scheduled for July 1963.{{sfn|History of the Mk 59 Warhead|p=18-19}}

During this study group, it was determined that the XW-56-derived ESD used in the XW-59 would be unsuitable for the Skybolt application due to the requirement for free-fall drop delivery option.{{sfn|History of the Mk 59 Warhead|p=18}} In March 1961, the Skybolt joint working group met and concluded the initial July 1963 deployment date was unrealistic as flight tests of the weapon had still not been conducted.{{sfn|History of the Mk 59 Warhead|p=19}} Further, due to the need for a special ESD, the XW-59 warhead for Skybolt was renamed the XW-59-X1.{{sfn|History of the Mk 59 Warhead|p=6}}

As the production date for Skybolt began to slip, first flight tests were scheduled for December 1963. Sandia objected to the planned program of only two flights, wanting eight to twelve test flights instead. In August 1961, first production date for Skybolt was rescheduled to April 1964 at Sandia's request.{{sfn|History of the Mk 59 Warhead|p=21}}

In December 1962, all effort on the XW-59-X1 was halted, and in March 1963 the Skybolt program and its warhead were cancelled.{{sfn|History of the Mk 59 Warhead|p=22}}

The W59 was {{convert|16.3|in|cm}} in diameter and {{convert|47.8|in|cm}} long, and it weighed {{convert|550|lb}}.{{cite web |first=Carey |last=Sublette |url=http://nuclearweaponarchive.org/Usa/Weapons/Allbombs.html |title=Complete List of All U.S. Nuclear Weapons |website=Nuclear weapon archive |date=12 June 2020 |access-date=2021-11-05 |archive-url=https://web.archive.org/web/20090227003412/http://nuclearweaponarchive.org/Usa/Weapons/allbombs.html |archive-date=2009-02-27}} From official documents, it had a design yield of {{convert|800|ktTNT}}.{{efn|The report states that the {{convert|550|lb|abbr=on}} warhead for Minuteman has a yield of {{convert|800|ktTNT|abbr=on}} and the {{convert|600|lb|abbr=on}} warhead had a yield of {{convert|1200|ktTNT|abbr=on}}.{{Cite report| title = DCI Briefing to Joint Chiefs of Staff| date = 1963-07-30| url = https://commons.wikimedia.org/wiki/File:JCS_briefing_(July_30,_1963).pdf| page=20| access-date = 2021-11-06| archive-date = 2021-11-06| archive-url = https://web.archive.org/web/20211106093822/https://commons.wikimedia.org/wiki/File:JCS_briefing_%28July_30,_1963%29.pdf| url-status = live}} The W59 is the only 550lb warhead for Minuteman.}} The weapon had both contact and airburst fuzing modes.{{sfn|History of the Mk 59 Warhead|p=16}}

The W59 was one of five nuclear weapon designs identified by researcher Chuck Hansen as using the common design Tsetse primary. Hansen's research indicates that the Tsetse primary was used in the US B43 nuclear bomb, W44 nuclear warhead, W50 nuclear warhead, B57 nuclear bomb, and W59.{{Cite journal| doi = 10.2968/057002015| issn = 0096-3402| volume = 57| issue = 2| pages = 52–55| last = Hansen| first = Chuck| title = Beware the Old Story| journal = Bulletin of the Atomic Scientists| accessdate = 2021-11-06| date = 2001-03-01| url = https://journals.sagepub.com/doi/abs/10.2968/057002015| archive-date = 2021-11-06| archive-url = https://web.archive.org/web/20211106093841/https://journals.sagepub.com/doi/full/10.2968/057002015| url-status = live}}

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.

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• Teller-Ulam design

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Category:Nuclear warheads of the United States

Category:Military equipment introduced in the 1960s