A Royal Navy Vanguard class submarine returns to Faslane after a 194 day patrol in September 2023. Image credit: Sheila Weir / X
Over the last few days the Royal Navy has had three of its Vanguard class nuclear armed submarines as sea. This is a very rare event. This note looks at the background to this unusual situation and offers some potential explanations for why three submarines may be at sea at this time.
Usual Vanguard class submarine routines
The Royal Navy has four Vanguard class submarines, which carry Trident nuclear-armed missiles. Of these, one is always at sea on nuclear armed patrol, and a second submarine (currently HMS Victorious) is in long-term deep refit at Devonport dockyard and unavailable for operations.
The other two submarines are usually berthed at Faslane submarine base. On return from patrol, a submarine will undergo repair and maintenance, usually lasting several months, meaning that it can not easily be sent to sea. Around one month before the next patrol is due to start, a submarine will start ‘work up’ activities – a series of exercises and drills to bring it up to readiness to depart on patrol. A few days after this submarine has left to take over a patrol, the submarine which has been relieved of patrol duties will return to Faslane.
As has been well documented, Vanguard class submarines are currently conducting long patrols of around six months duration, or even longer. This is believed to be because of delays and difficulties in submarine maintenance, which has an impact on submarine availability. These difficulties make it even more notable that three Vanguard class submarines are currently at sea.
Recent submarine movements and current situation
Nukewatch UK has observed the following submarine movements:
12 April 2026: Submarine left Faslane on patrol. Not believed to have returned yet.
18 April 2026: Submarine returned from patrol to Faslane.
3-8 September 2026: Submarine at sea from Faslane, probably on work-up trip.
9 September 2026: Submarine to sea from Faslane, probably on work-up trip.
20 September 2026: Submarine returns from sea to Coulport Explosives Handling Jetty.
12 October 2026: Submarine leaves Coulport and sails to sea.
14 October 2026: Submarine leaves Faslane and sails to sea.
As of 14 October there have been three Vanguard class submarines at sea: one on patrol, one possibly on work-up, and one for unknown reasons. This is a rare situation which usually only occurs when a) a submarine sails to the US submarine base at Kings Bay, Georgia to load up with Trident missiles (a missile test firing is usually conducted soon afterwards), or b) a submarine is participating in a joint exercise with US forces. According to Nukewatch records, the last occasion when three Vanguard class submarines were at sea was 22 October – 3 November 2022. Shortly after this the Sun newspaper reported that there had been a fire on board HMS Victorious while on patrol, causing the submarine to abandon the patrol. Separately the US Navy released a photo of a Vanguard class submarine on exercise in the Atlantic Ocean with a nuclear-armed US Ohio class submarine.
Possible explanations
Nukewatch has identified a number of possible explanations for this situation. These are listed below, in rough order of likelihood (most likely explanations first).
1. Submarine exercise. As was the case in 2022, it is possible that the third submarine is participating in an exercise. The US nuclear readiness exercise ‘Global Thunder 27’ is scheduled to take place in October 2026. This exercise is organised by US Strategic Command and in the past has included drills involving nuclear armed heavy bomber aircraft and submarines. NATO has recently concluded its annual ‘Steadfast Noon’ exercise, described as a “nuclear deterrence exercise”, which took place earlier in October. It is possible that the Royal Navy is undertaking exercises which co-incide with, or are otherwise linked to, these other nuclear exercises organised by NATO allies. UK aircraft have taken part in this year’s Global Thunder exercise, and also recently supported a French nuclear weapons exercise
2. Visit to Kings Bay. It is possible that a submarine is visiting Kings Bay to change its load of Trident missiles. Although the US Navy’s first Trident D5 missile life extension programme was completed in 2017, the Royal Navy has not published a timetable for operation of missiles with the life extension, and it is possible that it is lagging behind the US Navy’s programme. If this is the case, a submarine may be travelling to Kings Bay to load with missiles and / or take part in a missile test firing.
3. Submarine incident. It is possible that the submarine on patrol has suffered an unexpected breakdown or accident, and that the deployment of two other submarines may be linked to measures to replace it on patrol. This would not necessarily explain why two submarines have been deployed, unless there are concerns about the readiness and reliability of the replacement submarines.
4. Threat to submarines. It is possible that the Royal Navy believes that Faslane base and its submarines face an imminent threat of attack by hostile parties, and has sent them to sea in order to guarantee their safety. If this is the case, the security alert status of the Clyde submarine base would be expected to have been elevated.
5. Impending international crisis. The government may believe that an international crisis is on the horizon and has sent all its available nuclear armed submarines to sea, either to test their systems, have them at readiness to launch an attack, and / or send a signal to its enemies.
Information which helps to clarify matters may become available over the weeks ahead as further observations of submarine movements are recorded.
