Submarines - unseen and unheard, the Royal Navy.s submarine force can strike against ships and submarines, as well as supporting land operations against targets up to 1000 miles away with pinpoint accuracy. The Submarine Service also provides the UK.s strategic nuclear deterrent.
There are basically two types of submarines in service:

Strategic missile submarines (SSBN) Vanguard class

These remain the largest submarines in service in any navy except those of the USA and the Russian Federation. In order to maintain a high level of availability each boat is allocated two full crews, known as Port and Starboard. SSBNs are armed with the Trident D5 weapon, representing the UK.s sole strategic weapons platform.

Attack submarines (SSN)

The Astute class of SSN has been developed from the preceding Trafalgar class to incorporate the newly-designed reactor Core H. This will provide enough fuel for the submarine.s full 25-year service. With six weapons tubes and greatly increased weapons stowage, the Astute class carries much greater firepower than earlier classes. The weaponry will comprise Tomahawk cruise missiles and the Spearfish heavyweight torpedo. Improved technology means crew numbers have been reduced to 84 with available accommodation for 98. For the first time in an attack boat, all crew members will have their own bunks.