The Dreadnought programme is about the design, development and manufacture of four new Dreadnought class ballistic missile submarines. When they enter service in the early 2030s, replacing the Vanguard Class, they will be the largest submarines ever operated by the Royal Navy. The submarines will be built in 16 units, grouped into three ‘mega units’ (Aft, Mid and Forward) in order to optimise the overall build timeframe. Each submarine will be built by BAE Systems Submarines in Barrow-in-Furness and their nuclear propulsion systems will be built by Rolls Royce Submarines in Derby. The build phase for all four submarines will take approximately 20 years.