HMS Vigil: what are Royal Navy’s Vanguard-class submarines and how are they used in Trident nuclear programme?

Vigil, the BBC’s new six-part crime drama from the creators of Line of Duty, premieres over the bank holiday weekend with a double bill.

Starring Suranne Jones (Gentleman Jack) and Martin Compston (Line of Duty), the series is set aboard HMS Vigil, a Trident nuclear submarine.

But is HMS Vigil a real ship, and what are the Royal Navy’s Vanguard-class submarines used for? Here’s what you need to know.

What are Royal Navy’s Vanguard-class submarines?

The Royal Navy currently has four Vanguard-class submarines in active service.

The class was introduced in 1994 as part of the Trident nuclear programme - the UK’s nuclear deterrent.

The four submarines are: Vanguard, Victorious, Vigilant and Vengeance. Each one is a nuclear-powered ballistic missile submarine.

Each submarine was originally built with 16 missile silos but according to the 2010 Strategic Defence and Security Review , the number of operational silos fell to eight.

All four boats are based at HM Naval Base Clyde at Faslane, Scotland. The submarine class is scheduled to be replaced starting in 2028 with the Dreadnaught class.

In BBC’s Vigil, HMS Vigil is also part of the programme. This boat is a fictional Vanguard-class submarine and is not part of the UK’s real-life Trident nuclear programme.

How are the submarines used in Trident nuclear programme?

At any one time, three of the Vanguard-class submarines are armed with Trident II D-5 ballistic missiles. These are able to deliver thermonuclear warheads from multiple re-entry vehicles.

The principle of their role is known as continuous-at-sea-deterrence (CASD) in which at least one submarine is always on active patrol.

Two are in port at HM Naval Base Clyde or on training exercises. The fourth is kept in the UK where it receives servicing and maintenance.

Whilst out of patrol, a submarine is required to remain silent for three months. Only a select few people in the UK will know its current whereabouts.

Only the Prime Minister or a designated survivor can authorise the Chief of Defence Staff to order the missiles to be fired.

When does Virgil start on BBC One?

The first episode of Vigil will air on Sunday 29 August on BBC One at 9:00pm.

The second episode will air the following night on Monday 30 August on BBC One at 9:00pm.

The following episodes will air each week on Sunday evenings from then onwards.

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