The simultaneous deployment of the three submarines is rare, as the Royal Navy only needs to have one on patrol at any given time.

As of this week, three-fourths of the Royal Navy’s nuclear-powered ballistic missile submarines (SSBNs) are deployed around the world. That might sound impressive—until we clarify that it means three boats in total, as the UK military’s senior service operates just four Vanguard-class nuclear submarines. Those vessels maintain the United Kingdom’s continuous at-sea nuclear deterrent (CASD), a mission carried out without interruption since 1969. Only one submarine is needed for that task, so it is unusual that three are currently deployed at the same time.

The precise locations of the three submarines are unknown. The Royal Navy also has not indicated which of the submarines are carrying nuclear warheads—specifically the Trident II D5 ballistic missile, the United Kingdom’s standard second-strike SLBM. It is likely that two of the boats are armed with nuclear weapons, with the second preparing to relieve the first, and the third conducting post-maintenance sea trials or other work-up activity.

“The unusual deployment of most of the UK’s fleet suggests improved availability, which has been a problem for the Royal Navy’s submarine service in recent years. It will doubtless be noted by the UK’s enemies and its NATO allies,” Sky News reported.

The simultaneous deployment of three out of the UK’s four SSBNs is unusual, but not unprecedented. The last time three of the Vanguard-class submarines were at sea at once was in 2022, when one was wrapping up a patrol, another was beginning its deployment, and one was undergoing training. Still, the development signals that three boats are now available should the need arise.

The Times identified the three boats on patrol as the HMS Vanguard (S28), HMS Vigilant (S30), and HMS Vengeance (S31). The UK paper of record reported that the fourth Vanguard-class boat, HMS Victorious (S29), was at the Devonport shipyard “undergoing deep maintenance” and would not be ready for deployment in the near future.

The Vanguard-Class Submarine’s Specifications

• Year Introduced: 1996
• Number Built: 4
• Length: 491.8 ft (149.9 m)
• Beam (Width): 42 ft (12.8 m)
• Displacement: 14,000 tons surfaced/15,980 tons submerged
• Powerplant: Rolls-Royce PWR-2 pressurized water nuclear reactor
• Speed: 18 knots on the surface/25 knots submerged
• Range: Unlimited (nuclear-powered), except by supplies/crew endurance; standard deployments last 99 days
• Armament: 16 launch tubes for Trident submarine-launched nuclear missiles (SLBMs); four 21-inch torpedo tubes
• Crew: 135 (14 officers, 121 enlisted)

Each of the four Vanguard-class nuclear-powered submarines was built by Vickers Shipbuilding & Engineering, Barrow-in-Furness. They were designed with a 25-year service life, but will be nearly 40 years old when they are finally replaced by the future Dreadnought-class submarines in the early 2030s.

Long Deployments for the Royal Navy’s Submariners

The Royal Navy has extended the deployments of each of the four Vanguard-class boats in recent years, far beyond the planned 99-day patrols. In April, one of the four submarines returned to port at His Majesty’s Naval Base Clyde in Scotland following a 205-day patrol—more than double the expected deployment. Much of that time was spent underwater, where the crew can lose nearly all sense of time. Former UK Prime Minister Sir Keir Starmer greeted the crew when it arrived at the homeport of the UK’s submarine fleet.

According to British media reports, all of the nine most recent patrols have exceeded five months at sea, or 152 days or more, and six-month deployments have effectively become the new standard.

Having three boats in rotation could mean the deployments will be shorter, which will in turn improve the quality of life for the Royal Navy’s submariners.

“If this means the operational availability of those boats is going up then this is a good thing,” Tom Sharpe, who spent 25 years in the Royal Navy commanding four warships, told The Times. “This isn’t anything indicative or sinister, just routine operational scheduling.”

The Vanguard-class submarines were designed for 99-day patrols, and have food stores and freezers that can support only three to four months at sea. That means stores are packed throughout the boat, with passageways covered with canned foods and other dry goods. There is also no such thing as taking out the trash at sea!

About the Author: Peter Suciu

Peter Suciu regularly writes about military hardware, firearms history, cybersecurity, politics, and international affairs. He has contributed to dozens of newspapers, magazines, and websites over a 30-year career in journalism, including Forbes and Clearance Jobs. He is based in Michigan. You can follow him on Twitter: @PeterSuciu. You can email the author at Editor@nationalinterest.org.

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