 As such, the missile compartment is based on the same system used on the American , which is also equipped with the UGM-133 Trident II.This requirement led to the "Vanguard"-class design being significantly larger than the previous Polaris-equipped "Resolution" class, and at nearly 16,000 tonnes they are the largest submarines ever built for the Royal Navy.Prime Minister Thatcher laid the keel of the first boat, HMS "Vanguard", on 3 September 1986 at the Devonshire Dock Hall in Barrow-in-Furness.