Chilmark was the site of a major underground ammunition store since before World War II, built in a bathstone quarry site. By 1941 it seems to have evolved into an RAF bomb store.
The Home Office bunker known as RGHQ 7.1 was built on an adjoining site in the mid-1980s, to replace the former SRHQ at Ullenwood (near Cheltenham).
Along with most of the other RGHQs, it was closed in about 1992. It came onto the market in March 1997.