Mark 21 nuclear bomb
The Mark 21 nuclear bomb was a United States nuclear gravity bomb first produced in 1955. It was based on the TX-21 "Shrimp" prototype that had been detonated during the Castle Bravo test in March 1954. While most of the Operation Castle tests were intended to evaluate weapons intended for immediate stockpile, or which were already available for use as part of the Emergency Capability Program, Castle Bravo was intended to test a design which would drastically reduce the size and costs of the first generation of air-droppable atomic weapons (the Mk 14, Mk 17 & Mk 24). At long, in diameter, and weighing , the Mk-21 was half the length and one-third the weight of the Mk-17/24 weapons it replaced. Its minimum yield was specified at four megatons.
Castleshaw Roman Fort
Under the supervision of the University of Manchester, further excavation was undertaken on the site in 1957–61 and 1963–64. Between 1984 and 1988, Greater Manchester Archaeological Unit undertook excavations and restoration of the site. A group led by Professor Barri Jones – an expert on Roman Britain – was set up to co-ordinate the work. North West Water, then the owners of the site, ensured the area would not be used for agriculture. In an attempt to make the site accessible to the public, the outline of the fort and fortlet was marked out in low mounds and an education centre was set up nearby. The area beyond the fort was investigated for the first time in 1995–96; archaeologists were searching for a civilian settlement or "vicus" associated with the fort. Surveys revealed a settlement triangular in shape and to the south of the fort. The "vicus" is listed as a Scheduled Ancient Monument with the fort and fortlet.