A dockyard in Cumbria has been awarded a £200m contract to build a further nuclear-powered attack submarine.
A computer generated image of an Astute class submarine
HMS Audacious is the fourth Astute class vessel planned for construction at BAE Systems in Barrow.
Once in operation, the 7,800 tonne boats, equipped with the latest cruise missiles, will be the most capable ever deployed by the Royal Navy.
The first, HMS Astute, is due to be launched on 8 June 2007 - almost four years later than originally planned.
Astute class submarines will replace the Swiftsure and Trafalgar Class, which have been in service since the 1970s and 1980s.
They can circumnavigate the globe without needing to surface as they make their own air and water.
Accurate weapons systems mean that if positioned in the English Channel, their cruise missiles could pinpoint targets as far away as North Africa.
First Sea Lord and Chief of the Naval Staff, Admiral Sir Jonathon Band KCB ADC, said: "We need a versatile maritime force across the operational spectrum.
"Astute forms a key part of this future programme and is designed as a multi-role platform.
"The first of these immensely powerful submarines, HMS Astute, is launched next month and I look forward to her entry into service with her sisters, Ambush and Artful, and now the fourth of the class, Audacious.
"These boats will help protect Britain's interests overseas for decades to come."