By the end of 1940 the Main Office block was complete, and in December of that year the Unit 1 Sulphuric Acid Factory went into production with acid mixing for the Nitrocellulose and Nitroglycerine manufacturing. Five months later, the Pressure Oxidation Plant for the manufacture of Nitric acid came on stream. In August 1941 the Nitrocellulose and Nitroglycerine plants were operational and were soon working 24 hours a day on a three-shift pattern. At the same time, Unit 2 of the factory was almost completed, so RNPF Caerwent was now virtually operational.