Royal Navy Nuclear Sub Sets 204-Day Patrol Record

A recently returned Vanguard-class submarine has reportedly just set the record for the longest patrol by a British boat carrying the nation’s independent nuclear deterrent.

The submarine, believed to be HMS Vanguard, sailed back into HM Naval Base Clyde — a.k.a. Faslane — on Monday (March 17) after a 204-day patrol which apparently began back in August 2024.

Her return was enabled after another boat in the class sailed last week, maintaining the U.K.’s continuous-at-sea nuclear deterrent.

Media reports suggest the sub’s food storage facilities were originally designed to support patrol durations of about three to four months; it is unclear whether in this case the unusual step was taken of surfacing and resupplying the vessel halfway through during her marathon stint at sea.

It’s thought that each of the last eight Vanguard-class submarine patrols have all exceeded five months in duration.

Britain has four Vanguard-class submarines in active service: HMS Vanguard, HMS Victorious, HMS Vigilant and HMS Vengeance. They are powered by a pressurised water reactor, giving them a maximum speed in excess of 25 knots underwater, and meaning their range and sailing duration is limited only by food supplies and mechanical integrity.

They are equipped with 16 ballistic missile tubes, eight of which are loaded with the Trident II submarine-launched ballistic missiles; each missile has up to eight nuclear warheads. 

The submarines also carry the Spearfish heavyweight torpedo, which has a range of up to 35 nautical miles.

The boats had an originally intended service life of 25 years, meaning the newest, HMS Vengeance, would have been due to be taken out of service last year.

The boats are now due to be replaced by the forthcoming Dreadnought-class submarines being built by BAE Systems; the first of these vessels is expected to be commissioned in the 2030s.