The Vanguard class is the largest submarine type ever constructed in the UK, and the third largest type of vessel in Royal Navy service. However, it is cloaked in tight secrecy. Despite the ending of the Cold War and the downgrading of its strategic mission, details on Vanguard weapon systems and patrols are still highly classified.

All four of the boats, HMS Vanguard, HMS Victorious, HMS Vigilant and HMS Vengeance, were built by Vickers Submarine Engineering Limited (now BAE Systems Marine) at its dockyard in Barrow-in-Furness, Cumbria. Such was their size that a special production facility, the Devonshire Dock Hall, had to be constructed. The boat's large hull was prompted by the Trident D5 Submarine-Launched Ballistic Missile (SLBM), of which it can deploy 16. However, the vessels patrol with a smaller complement of crew than that of the previous Resolution class (132 as opposed to 149).

The first major transition from Polaris to Trident occurred in 1996, when HMS Victorious was deployed on patrol with a complement of Trident SLBMs. Trident has since become the sole component of the UK's nuclear deterrent, following the decommissioning of the WE177 tactical nuclear gravity/depth bomb in 1998, as part of the UK Strategic Defense Review. Furthermore, the Vanguard class boats had their readiness to fire changed from a matter of minutes to a matter of days according to the UK Secretary of State for Defense.

The Vanguard-class missile suite contains 16 tubes and is based on the 24-tube design which the US Navy deploys on its Ohio class boats. The Trident missile system was built by Lockheed Martin, and is technically leased from the US. The Trident D5 is a MIRV (Multiple Independently-targeted Re-entry Vehicle) system, capable of deploying 12 warheads per missile.

Missile maintenance occurs in the US. However, the UK Atomic Weapons Establishment at Aldermaston undertakes all the design, construction, installation and maintenance of the warheads.

Each Vanguard-class submarine can carry a maximum of 192 nuclear warheads, although the Royal Navy originally insisted that each boat would carry no more than 96, deployed across eight missiles. Since the Strategic Defense Review, this has been further reduced to 48 warheads per boat, spread across four missiles. Although the Ministry of Defense refuses to comment on how many missiles are deployed when a boat is on patrol, it has indicated that the complement of Trident missiles now only carries one warhead per missile, which is probably in the sub-strategic kiloton range. A single Vanguard-class boat is on deterrence patrol at any one time, and a reserve boat is also available.

As well as having a new strategic weapons system, the Vanguard also features several other new systems. These include a Rolls-Royce nuclear Pressurized Water Reactor propulsion system, a new tactical weapons fit including Tigerfish and Spearfish torpedoes for short and medium defense. Tigerfish has a range of 13-29 km depending on the homing configuration, while Spearfish can hit targets up to 65 km away. The submarine also features a greatly improved Electronic Counter Measures (ECM) suite, and state-of-the-art attack and search periscopes. These are fitted with a TV camera and thermal imager as well as the traditional optical channel.