On 1st October, a Vanguard-class Royal Navy submarine returned to Faslane following a 203-day patrol, which was one day short of the record duration set by its immediate predecessor. These patrol lengths far exceed the originally planned three-month threshold.
These lengthy deployments reflect the United Kingdom’s long-term nuclear policy named Operation RELENTLESS, in effect since April 1969 and executed by the Royal Navy. Under this policy, at least one nuclear-powered and nuclear-armed submarine is continuously on patrol at sea, in a posture known as Continuous-at-Sea Deterrence (CASD). The current Vanguard-class submarines assumed this role in 1994, succeeding the Resolution-class. However, the operational lifespan of these Vanguard-class submarines has now significantly surpassed the initially intended 25 years.
The increasing duration of patrols is also driven by other interlinked challenges. The Royal Navy continues to face difficulties recruiting submariners; reflective of broader recruitment shortfalls across the armed forces. Furthermore, these extended patrols can further deter recruitment, effectively creating a self-reinforcing cycle in which long patrols lowers recruitment/retention, and low recruitment/retention extends patrols. Prolonged maintenance periods needed for the aging Vanguard fleet also play a role in lengthening these patrols. In the weeks following the return of this Vanguard-class submarine, First Sea Lord General Sir Gwyn Jenkins announced a Submarine Maintenance Recovery Plan to resolve these excessive maintenance periods of submarines. Central to this initiative is a “rethink” of the Clyde 2070 infrastructure programme, formally launched in July 2025, which aims to upgrade infrastructure in Faslane in preparation for the future Dreadnought and Astute-class submarines.
Earlier in 2025, the Ministry of Defence declined to confirm whether steps were being taken to reduce patrol durations; citing the need to protect operational effectiveness and safety. This is significant as such extended deployments impose substantial psychological pressures on submarine crews and their families, and these stressors can also heighten risks to nuclear safety. The 2024 Defence Nuclear Enterprise Command Paper, presented by the Secretary of State for Defence, set out the measures needed to sustain the UK’s nuclear weapons enterprise, including the necessary training and education for submariners, as well as initiatives to improve their skills, recruitment, and retention. However, as noted by a former submariner, the selection process does not include comprehensive psychological screening, and the Command Paper made no reference to measures to assess mental health as a part of the selection or retention plans. These omissions and long patrols indicate that the mental well-being of submarine crews may be compromised in the pursuit to sustain the tempo of CASD, hence rendering CASD an effort that carries mounting material as well as human costs.