Sailors returning from a patrol that formed part of the longest sustained military operation undertaken by the UK have been greeted by the Deputy Prime Minister.

The Royal Navy’s latest nuclear deterrence submarine patrol was welcomed home at Clyde Naval Base, near Faslane, Argyll and Bute, on Sunday by Oliver Dowden and First Sea Lord, Admiral Sir Ben Key.

The Vanguard-class ballistic submarine completed their silent mission beneath the waves, carrying the Trident missile system.

It came in the 55th year of Operation Relentless, under which a British submarine carrying the nation’s ultimate weapon has patrolled the world’s oceans unseen, undetected and ready to strike since 1969.

Operation Relentless is the longest sustained military operation undertaken by the UK. Known as the Continuous at Sea Deterrent, it is the unyielding responsibility of the Royal Navy and the Submarine Service to ensure these patrols of national importance never cease.

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Mr Dowden said: “I am delighted to be here to welcome home our sailors as they return from patrol.

“The Continuous At Sea Deterrent is enormously important to the United Kingdom and I am humbled by their service.

“I do not underestimate the demands on our people and their families in their commitment to delivering this capability.”

The Vanguard submarine arrives back at the Clyde Naval Base (Bill Spurr/PA)

Sir Ben said: “It’s a great privilege for me to welcome home the returning ship’s company.

“They have done an exceptional job and I never fail to be impressed by their dedication and professionalism.

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“I also pay immense tribute to their families and thank them for their support.

“We should never underestimate the huge national effort that goes into this endeavour. It is through the commitment of all of those across the Defence Nuclear Enterprise, our industrial partners and across Government that we are now in our 55th year of unbroken deterrent patrols.”

A new class of ballistic submarine, the Dreadnought class, is under construction and is expected to replace the Vanguard class by the 2030s.