I have found two references to the manufacturing of guns at R.O.F. Cardiff.
“It was originally established in 1940 as a Royal Ordnance factory, manufacturing field guns and other weaponry.”
http://news.bbc.co.uk/2/low/uk_news/wales/2305833.stm
“THE Atomic Weapons Establishment in Cardiff began its life as a Royal Ordnance factory in 1940. During World War II, it played a vital role, manufacturing anti-tank weapons. At the peak of wartime production, there were more than 3,000 employees, 90 per cent of them women, turning out more than 1,700 guns a month.”
http://www.highbeam.com/library/doc0...yword=&teaser=