Editing Nuclear weapon design (section)

===Wire safety method===
In the last test before the 1958 moratorium the W47 warhead for the Polaris SLBM was found to not be one-point safe, producing an unacceptably high nuclear yield of {{convert|200|kg|lb|abbr=on}} of TNT equivalent (Hardtack II Titania). With the test moratorium in force, there was no way to refine the design and make it inherently one-point safe. A solution was devised consisting of a [[boron]]-coated wire inserted into the weapon's hollow pit at manufacture. The warhead was armed by withdrawing the wire onto a spool driven by an electric motor. Once withdrawn, the wire could not be re-inserted.<ref>Chuck Hansen, ''The Swords of Armageddon'', Volume VII, pp. 396–397.</ref> The wire had a tendency to become brittle during storage, and break or get stuck during arming, preventing complete removal and rendering the warhead a dud.<ref name="dud"/> It was estimated that 50–75% of warheads would fail. This required a complete rebuild of all W47 primaries.<ref>{{cite journal |last1=Harvey |first1=John R. |last2=Michalowski |first2=Stefan |title=Nuclear Weapons Safety:The Case of Trident |journal=Science & Global Security |volume=4 |issue=3 |pages=261–337 |bibcode=1994S&GS....4..261H |doi=10.1080/08929889408426405 |date=1994 |url=https://scienceandglobalsecurity.org/archive/sgs04harvey.pdf |url-status=live |archive-url=https://web.archive.org/web/20121016101827/http://www.princeton.edu/sgs/publications/sgs/pdf/4_3harvey.pdf |archive-date=2012-10-16}}</ref> The oil used for lubricating the wire also promoted corrosion of the pit.<ref>{{cite book |isbn=978-0521054010 |title=From Polaris to Trident: The Development of the U.S. Fleet Ballistic Missile Technology |url=https://books.google.com/books?id=95eoQSNDp6gC&q=warhead+corrosion&pg=PA214}}.{{dead link|date=November 2016|bot=InternetArchiveBot |fix-attempted=yes}}</ref>