Three of Britain's four nuclear deterrent submarines are reportedly at sea at the same time, an "unusual" move, with at least one understood to be carrying ballistic missiles armed with nuclear warheads.
The Times reports that experts believe the other two vessels could be conducting sea trials and preparing for future operations. The Royal Navy has declined to confirm the submarines' tasks, citing security reasons.
Unusual deployment and maintenance
The remaining Vanguard-class submarine, HMS Victorious, is currently undergoing deep maintenance in Devonport. A Navy source described the presence of the three submarines at sea as unusual but refused to give a reason for the move.
A second former senior naval source told The Times that the Royal Navy had been operating in "2BA" for a prolonged period, referring to the availability of two boats at any one time.
Fleet details and deterrence policy
The Royal Navy operates four Vanguard-class submarines - HMS Vanguard, HMS Victorious, HMS Vigilant and HMS Vengeance - which carry the Trident missile system. Under the UK's Continuous At-Sea Deterrent policy, at least one nuclear-armed submarine remains on patrol at all times.
The fleet's availability has been affected by lengthy maintenance periods. Patrols have also grown longer, with one submarine returning after a record 205 days at sea in 2026. Sea trials are used to test a submarine's systems and performance before it undertakes operational duties.
Official response
A Ministry of Defence spokesperson told the Mirror: "Our nuclear deterrent is the cornerstone of our national security, protecting the UK and our NATO allies every moment of every day."
"We remain the only European ally to commit its nuclear deterrent to the defence of NATO. This means that all NATO Allies already benefit from the protection of our nuclear deterrent."
