Filling Factories in the United Kingdom A Filling Factory was a munition s factory which specialised in filling various munitions , such as bombs , shells , cartridges , pyrotechnics , screening smokes , etc . In the UK , in both World Wars , the majority of the employees were women . In the UK , in World War I , such a factory belonging to the Ministry of Munitions was known as a National Filling Factory . In the UK , in World War II , such a factory belonging to the Ministry of Supply was known as a Royal Filling Factory ( RFF ) , or a Royal Ordnance Factory ( ROF ) . In terms of organisation , they were part of the Royal Ordnance Factory organisation . Particularly , in World War II , the filling of screening smokes and other pyrotechnic devices was also carried out by fireworks manufacturers ; parts of this article do not apply to these fireworks filling factories . Raw materials . The Filling Factory ' s raw materials , such as TNT , RDX , or propellants , such as cordite , were manufactured in National Explosives Factories ( World War I ) or Explosive ROF s ( World War II ) and transported , by railway trains , to the Filling Factories for filling into munitions , produced at other plants . High - explosive s , such as TNT , had to be heated to melt them and the liquid was poured hot into heated shell cases . Care had to be taken to ensure that there were no voids in the poured explosive charge as this could lead to the shell detonating in the gun barrel during firing . Shells and gun cartridge s were manufactured in the UK , in World War II , by both the Engineering ROF s and private steel works / forging companies . It is believed that the empty brass cartridge cases for small arms were made at the Small Arms Ammunition Factories . The Filling Factories produced their own pyrotechnics , such as fuse s and screening smokes ; as many of these were sensitive materials . They were then filled or assembled directly into the munitions . They also would have sewn cotton bags for filling with primer composition or cordite charges . Filling Groups . Filling factories had a large number of buildings . Buildings were needed on the various Groups for filling of munitions . Explosives magazines were required by each Group to store the incoming explosive materials and to store the outgoing filled shells or gun cartridges , usually packed in ammunition boxes . Storage buildings were also needed on each Group to store the incoming empty shells , or cartridges , and the empty ammunition boxes . For safety purposes , munitions were segregated into different compatibility Groups . A World War II Filling Factory would generally fill several different Groups of Munitions ; and these Groups would be located in different geographical areas within the Danger Area of the Filling Factory . The World War II Groups were : In addition , a Filling Factory would have provision for limited proofing and testing of its munitions ; and burning grounds for disposal of waste explosive material . Outside of this Danger Area , but still within the factory site , would be located : UK World War I National Filling Factories . It is believed that the Ministry of Munitions owned up to 12 factories . UK World War II Royal Ordnance Factory , Filling Factories . Some of these Filling Factories were temporary " war duration " only factories and they closed after the end of World War II . Other Filling Factories were designed to be permanent and to remain open after the War . However only ROF Glascoed is still open and is now part of BAE Systems . Twenty World War II Filling Factories were planned , but only 16 were built . The two largest UK Filling Factories were : The other filling factories were :