The Defence Secretary has paid tribute to the Royal Navy nuclear submariners who have been patrolling waters around the world for 50 years.
It is the longest sustained military operation ever undertaken by British forces.
Nuclear deterrent patrols have been performed around the clock since 1969.
Since then there has always been one submarine from Clyde Naval Base carrying out Operation Relentless.
Gavin Williamson has thanked personnel who have been involved in the mission:"Operation Relentless is truly a national endeavour, from the families and friends who have supported our submariners for the past 50 years, to the thousands of British workers who continue to ensure our boats are among the best in the world," he said.
"As we to look to the future, it is important we acknowledge the incredible commitment thousands of men and women have made in the past and continue to make, 24 hours a day, seven days a week."
The Defence Secretary's comments come ahead of events across the UK celebrating half a century of the Continuous At-Sea nuclear deterrence.
Events to mark their commitment and success include services of thanksgiving in London and Edinburgh, a parade through the home of the deterrent force on the Clyde and a new commemorative award for the crew.
The First Sea Lord Admiral Sir Philip Jones says the 50th anniversary year presents a valuable opportunity to recognise and thank the Naval Service and their families.
He launched the year of commemoration by presenting new ‘badges of honour’ to veterans of patrols on a visit to HMS Vengeance, one of the four Vanguard-class submarines needed to provide the continuous at-sea deterrence.
Up until now, submariners who complete a single patrol have been awarded a pewter pin and those achieving 20 or more patrols presented with a gold deterrent pin. The new silver award bridges the gap between the two, being awarded after ten patrols.
Six submariners received the new silver pin from Admiral Jones, including Coxswain Daryn Mathieson.
He joined the Submarine Service in 1992 and has completed 18 deterrent patrols which is the equivalent of nearly five years submerged. He said: "It means a lot to receive my silver deterrent pin on the 50th anniversary of deterrence patrols.
"Fifty years is a real achievement and I’m proud to have played even a small part."