ROF Bridgend ROF Bridgend , ( Filling Factory No . 2 ) , located in Bridgend , South Wales , was one of the largest of sixteen World War II , UK government - owned , Royal Ordnance Factory munition s Filling Factories . Of great significance to the Britain ' s war effort , at its peak of production it employed around 40 , 000 people — said to be the largest ever factory in Britain ' s history . Background . At the end of World War I , much of Britain ' s armaments manufacturing capacity was run down , as its capacity was no longer needed . In the period leading up to World War II , consideration was given to Britain ' s war capability . As shown in the Spanish Civil War , the Luftwaffe were more than capable of accurately bombing many of Britain ' s key installations , which were also undersized to meet forecast required volumes . In 1935 , it was therefore agreed to keep armaments research at the Woolwich Arsenal in south - east London , while production would be transferred to two new factories at ROF Chorley in Lancashire ( Filling Factory No . 1 ) and ROF Bridgend in Glamorgan ( Filling Factory No . 2 ) . As war planning progressed , it would be realised that this plan was flawed in both sustainability and capacity , and additional facilities would have to be built . Staff from the Royal Arsenal helped design and , in some cases , managed the construction of many of the new Royal Ordnance Factories ( ROFs ) and ROF Filling Factories . Just over 40 ROFs were opened by the end of World War II , nearly half of them Filling Factories , together with a similar number of factories built and run by private companies , such as ICI ' s Nobel Explosives ( although these explosive factories were not called ROFs ) . Development . Bridgend was chosen for three main reasons : In April 1936 , of land in Waterton was compulsorily purchased . The site chosen was farmland next to the Great Western Railway South Wales Main Line , which offered additional benefits . Located on what was a reclaimed marshland , the resultant dampness often resulted in the area being covered in a light mist or fog , which further protected it from bombing . Further acreage was purchased in Brackla , leading to the development of ROF 11 and ROF 41 . In April 1937 , the Great Western Railway began constructing the of internal railway needed to supply the sites . This included a marshalling yard at the main site , sidings at Brackla Ridge , and the construction of Tremains halt near Waterton for worker access . A footbridge was also constructed here , the remnants of which can been seen today . Gee Walker & Slater Ltd , and Sir Lindsay Parkinson & Co Ltd were the contractors awarded the project to build ROF 53 . Sir Robert McAlpine & Sons Ltd won the contract to build ROF 11 and ROF 41 , and the magazine tunnels . In all , the complex consisted of over 1000 buildings , serviced by of roads . By 1940 , the sites were in full production , with nearly 40 , 000 people working at the factory , the largest single - site employer in the country . Closure . ROF Bridgend stopped production in 1945 , having been designated a " War Duration Only " ROF . It remained open as a store until it was closed in 1946 , when it was broken up and sold to property developers . Many of the specialised buildings were simply bulldozed , and like many of the former ROFs it became an industrial estate , now designated as Bridgend Industrial Estate . The administration buildings were taken over after the war to become the Glamorgan County Police Headquarters , which are now the South Wales Police headquarters . The land between the two former facilities to the south of Brackla Hill , was developed as a large housing complex , now simply called Brackla .