The decision to purchase the US Trident SLBM system by the Thatcher administration required a new class of ballistic missile subs to equip them. The result was the Vanguard-class of four subs, a one-to-one replacement of the preceding Resolution-class. Compared to the US equivalent, the Ohio-class, the Vanguard subs are smaller (though still much larger than the Resolutions) and can carry only 16 Trident missiles, rather than 24. This nevertheless allows a maximum of 192 warheads although due to strategic arms limitations treaties and defense reviews, no more than 48 are ever carried. Aside from this, Tigerfish and Spearfish torpedoes can be carried. The Vanguard-class is powered by a Rolls-Royce PWR2 nuclear reactor driving two GEC turbines. This allows them to circumnavigate the world 40 times without refueling. As is typical in modern British submarines, pump jet propulsion is used (via a single shaft) for quieter operation, and these are the first SSBNs in the world to do so. Other equipment include CK51 and CH91 periscopes with TV and thermal imagery and the Thales Type 2054 composite sonar system. The four Vanguard boats currently form the backbone of Britain's nuclear deterrent although there are plans to develop an eventual successor although the political viability of Trident (as well as its basing in Falsane, Scotland) remains in question.

None of the Vanguard boats have used in combat. The lead ship HMS Vanguard suffered a collision with the French SSBN Triomphant (its direct equivalent and also the lead ship of its class) in the Atlantic in February 2009 but was able to return to port for repairs.