It is intended to deter a potential enemy because they cannot ensure eliminating the entire stockpile in a first strike if a ballistic missile submarine remains undetected.

Under the continuous at sea deterrence policy, at least one Vanguard-class SSBN is kept on patrol with up to 16 Trident missiles sharing up to 48 warheads from the stockpile at any given time.

[11] The majority of this system is based in Scotland at HMNB Clyde (HMS Neptune), which includes the Faslane home of the Vanguard submarines, and at RNAD Coulport on Loch Long.

[16] In May 2011 the government approved the initial assessment phase for the new submarines and authorised the purchase of long lead-time items including steel for the hulls.

In May 2015 the Conservative Party won the UK General Election on a manifesto which included a commitment to maintaining a CASD with four Successor submarines.

[22] These costs do not include the related Trident missile renewal, new infrastructure projects at the re-nationalised Atomic Weapons Establishment, and new nuclear fuel production facilities at Rolls-Royce.

[22] Crispin Blunt, Chair of the Foreign Affairs Select Committee, estimated in July 2016 that the renewed deterrent lifetime cost would be £179 billion.

[23] A January 2018, the National Audit Office expressed concern about the programme's spending profile, including that it was "unaffordable in the early years of the project" within the MOD allocated budget.

[26] Although PWR2 and PWR2b (a derivative with improvements) designs were considered, the PWR3 was chosen for easier operations, longer service life and reduced maintenance costs, with 30% fewer parts.

[37] However, the Ministry of Defence commented that "the Dreadnought programme remains on track to deliver to schedule, with the first in class expected to enter service in the early 2030s.

[28] In January 2025, Rolls Royce was awarded a £9 billion contract by the MOD, covering research, design, manufacture and support of all nuclear reactors in Royal Navy submarines.

The contract, named “Unity”, covers a period of 8 years, and will continue to support the delivery of the reactors for Dreadnought class submarines.