The Vanguard class are the Royal Navy's current nuclear ballistic missile submarines (Ship Submersible Ballistic Nuclear or SSBN), each armed with up to 16 Trident II Submarine-launched ballistic missiles (SLBMs). The class was introduced in 1994 as part of the UK government's Trident nuclear weapons programme.

The class includes four boats: Vanguard (S28), Victorious (S29), Vigilant (S30), and Vengeance (S31), all built at Barrow-in-Furness by Vickers Shipbuilding and Engineering Ltd between 1986 and 1999.

All four boats are based at Her Majesty's Naval Base Clyde (HMS Neptune), 25 miles (40 km) west of Glasgow, Scotland. Since the decommissioning of free-fall nuclear bombs in 1998, the Vanguard submarines' Trident SLBM system is the UK's only nuclear deterrent.

The Vanguards were designed from the outset as an unlimited-range nuclear powered ballistic missile submarine, unlike the previous Resolution class which was adapted from the then existing Valiant class and the American Lafayette class of nuclear powered fleet ballistic missile submarines (SSBN in US terms).

At 149.9 metres long and 15,980 tonnes submerged displacement the Vanguards are roughly twice the size of the Resolutions, and are the third largest submarines ever built, by displacement when surfaced, after the Russian Typhoon and American Ohio classes. The great increase in size is largely related to much larger size of the Trident D-5 missile as compared to Polaris.

The Vanguards were designed and built at Barrow-in-Furness by Vickers Shipbuilding and Engineering Limited (VSEL), now BAE Systems Submarines. The Devonshire dock hall was built specifically to build these submarines. The missile compartment is based on the system used on the Ohio class, though only 16 missiles are carried rather than the 24 of the Ohio.

In addition to the missile tubes the Vanguard class is fitted with four 21 inch (53.3 cm) torpedo tubes and carries the Spearfish heavyweight torpedo, allowing it to engage submerged or surface targets at ranges up to 65 kilometres (40 miles). Two SSE Mark 10 launchers are also fitted to allow the boats to deploy Type 2066 and Type 2071 decoys, and a UAP Mark 3 electronic support measures (ESM) intercept system is fitted.

HMS Vanguard, Victorious, Vigilant and Vengeance were commissioned in 1993, 1995, 1996 and 2000 respectively.

A new pressurised water reactor, the PWR 2, was designed for the Vanguard class. This has double the service life of previous models, and it is estimated that a Vanguard class submarine could circumnavigate the world 40 times without refuelling.

This should allow the class to carry out their entire service life without the need for expensive refuelling. The reactor drives two GEC turbines linked to a single shaft pump jet propulsor.

This propulsion system gives the Vanguards a maximum submerged speed of 25 knots. There are two Paxman diesel alternators and two turbo generators from WH Allen for backup