Most of Britan’s nuclear missile submarine fleet now at sea

Three of the Royal Navy’s four Vanguard class ballistic missile submarines are at sea at the same time, an arrangement naval sources described as unusual, according to reporting in The Times.

One of the boats is understood to be conducting the deterrent patrol, carrying Trident II D5 missiles, which is the task the Royal Navy has maintained without a break since 1969. The other two are believed to have been on sea trials and preparing to take over the patrol. HMS Victorious, the fourth boat, is at Devonport undergoing maintenance and was not among those at sea.

The Ministry of Defence declined to comment.

Having three boats out at once is not a sign of extra capacity, though, as the Vanguard class was designed around a four boat cycle in which one submarine is on patrol, one is working up or recovering, one is in training or trials, and one is in deep maintenance, and the fourth hull is what keeps continuous at sea deterrence going as the submarines age. Running three at sea at the same time means the cycle has been compressed, and it is as consistent with pressure on availability as it is with a deliberate signal.

The Times was told by a former senior naval source that the service had been operating in what submariners call 2BA, or two boat availability, for a prolonged period. In that condition only two of the four boats are available for operational tasking at any time, which leaves no margin, because a defect on the boat at sea has to be covered by a single relief.

The strain is visible in how long the boats are staying out, Navy Lookout reported in March 2025 that a Vanguard class submarine had returned to the Clyde after 204 days, breaking a record set in 2023, and patrols of more than two hundred days have since been reported again. Deterrent patrols were historically planned around three months. Crews now routinely spend five months or more submerged with no contact with their families.

Forces News reported last week, in an account of life aboard the boats, that Commander Roger Ireland, a retired submariner who served on the earlier Resolution class, described the length of modern Vanguard patrols as horrendous. Resolution boats carrying Polaris went out for around eight weeks at a time.

Maintenance has been the other great difficulty, and HMS Vanguard emerged from a refit at Devonport in 2023 that took around seven and a half years against a planned three and a half, after an unscheduled nuclear refuelling pushed the cost from roughly £200 million towards £500 million, as this publication reported when she sailed.

The four Vanguards entered service between 1993 and 1999 and were designed for around twenty five years each. All four are now beyond that, and they must hold the deterrent until the Dreadnought class arrives from the early 2030s. The Defence Investment Plan commits £63 billion over four years to the nuclear enterprise, covering Dreadnought, SSN-AUKUS attack submarines, a new sovereign warhead and the infrastructure behind them.