The Duke of Cambridge and new Defence Secretary Penny Mordaunt have heard of the pride and sacrifice that has gone into delivering five decades of Britain's continuous at-sea nuclear deterrent.
William and Ms Mordaunt, in what is believed to be her first official engagement since becoming Defence Secretary this week, were at a Westminster Abbey service to recognise the commitment of the Royal Navy in maintaining Operation Relentless - the longest mission in the history of the services.
Op Relentless is Britain's continuous at-sea nuclear deterrent, and has been maintained by the Royal Navy for 50 years.
Since April 1969, for 24 hours a day, seven days a week, 365 days a year, at least one UK ballistic missile submarine has been on patrol beneath the waves of the world's oceans.
Ms Mordaunt had earlier announced that the fourth Dreadnought submarine is to be named HMS King George VI. She added: "We pay tribute to those incredible crews, their supportive families, the Royal Navy and the thousands of industry experts who will continue to sustain this truly national endeavour for many years to come."
Prince William, as commodore-in-chief of the submarine service, gave a reading during the service.
Rear Admiral Tim Hodgson, the Ministry of Defence's submarine capability director told the congregation: "The boats themselves are the work of a nation, set to task five decades ago to deliver complex machines at the forefront of modern-day technology.
"People across the country are united in an often unseen, quietly acknowledged purpose of delivering our deterrent and the surety it brings."
Leading engineer technician Edward Owen spoke of his pride but also the "large personal sacrifice" which is involved in being part of this life.
It includes being on patrol without phone calls, emails and social media, a lack of sunlight, limited personal space and long periods away from family, friends and loved ones.
He praised families at home for carrying "the heaviest burden" and pointed out that in the last 11 months he had spent only eight days with his girlfriend and had missed her birthday and Christmas.