Why are three of the UK’s four nuclear deterrent submarines at sea?

What happened: The UK deployed three of its four Vanguard-class nuclear submarines at sea at the same time, the first such occurrence in five years, The Times reported. HMS Vanguard, HMS Vigilant and HMS Vengeance are at sea, while HMS Victorious is in maintenance. Key numbers: Three of four submarines deployed, first time in five years. Why it matters: A navy source called the deployment "unusual." It raised questions over whether the UK changed its defence posture after Defence Secretary Wes Streeting warned Britain should be prepared for war.

The UK deployed three of its four Vanguard-class nuclear submarines at sea at the same time, the first such occurrence in five years, The Times reported. HMS Vanguard, HMS Vigilant and HMS Vengeance are at sea, while HMS Victorious is in maintenance.

A navy source called the deployment "unusual." It raised questions over whether the UK changed its defence posture after Defence Secretary Wes Streeting warned Britain should be prepared for war.