The former World War Two Royal Ordnance Factory at Brackla, used for filling and storing naval shells, was a part of the ROF at Waterton (nprn 91719). At its peak, some 40,000 people worked in the two factories - the highest ever employed in one establishment in the UK. Formerly connected by a siding from the Barry Railway, it covered an area of approximately 1.5km E-W x 1.5km and is now largely rebuilt as an industrial estate, although some remnants e.g. buildings, air raid shelters, pill boxes, rail served underground magazines in the north scarp of Brackla Hill, remain. The associated research laboratories were at Ton-du House (nprn 20074) some 5km to the NW.
B.A.Malaws, RCAHMW, 24 March 2003.

Sources:

M. J. Clubb, 'The Welsh Arsenal: The Story of the Bridgend Munitions Factory, ROF 53, and the People Who Worked There', (Gwasg Blaen-y-Wawr, 2007)