They did 60 days without touching land. “I think we still hold the record in the Navy.” On the Pacific, they withstood hundreds of kamikaze raids, yet the men still slept on the deck because their quarters were so overcrowded and  hot.

It was a long way from home for this young man – boy, really – from Pembroke Dock, Wales. But even before joining up, Mullins had first-hand experience of the horrors of the Second World War. Aged 14, he’d signed up to be a messenger boy with his fellow senior scout, a boy called Arthur. Half an hour after Mullins and Arthur were sent on different jobs while their town was being bombed, Arthur was killed. “Fourteen years of age,” Mullins repeats in his slow, gravelly voice. We are silent for a long moment.

Once the war had ended, life got a little better aboard ship. They picked up the Duke and Duchess of Gloucester for a visit to Australia (and Mullins is pictured with them in an image he shows me). They docked in South Africa to pick up gold bullion that the British government, fearing invasion, had stashed there for safekeeping.

“You were walking up the gangplank with a nice gold nugget under your arm,” recounts Mullins with relish. “There were so many armed sentries posted around us. And we carried billions of pounds’ worth of gold up that gangplank.”

Mullins’ daughter, Jo, 61, works in the care home and is sitting beside him. She’s suggested he write down his experiences. “I’ve never given it a thought,” says her father. But perhaps he should. They’re riveting stories, after all. And, as he observes, “You tend to forget half of it!”

Disbelieving, I start to laugh. “Well, you do!” he protests. “1945 – how many years ago was that?!” It’s so long ago that it’s hard to do the maths. Now he’s laughing, too.

His granddaughter, Hayley Moseley, 37, is a designer here at The Telegraph. Mullins has always been a grandfather to her, rather than a veteran, and it was only when Hayley reached her 20s that she began asking more questions. In return, Mullins told her more detailed stories.

“There’s a different side to my granddad,” she says. “I feel really proud of him. I don’t know why he doesn’t like to talk about it very much. Maybe the things Grandad Geoff has seen or lived through during his service are just too painful and he doesn’t want to talk about them, and you have to respect that.

“But I think he tells it in a way that’s educational, and it makes us realise what he did and what he saw in order for us to have a better life.”

Hayley hopes to document it all in a book. “He is our longest-living relative now. I think it’s important to have a memory of it and to pass it on one day.”

It disappoints her grandfather when he sees people on quiz shows displaying ignorance of the Second World War, but we ought not to assume that this is a new phenomenon.

“I’m as bad myself as regards the ’14-18 war. Other than on Armistice Day, I never, as a nipper, thought about it.”

The Royal Hospital Chelsea is welcoming applications to become a Chelsea Pensioner. Call 020 7881 5204 or email admissions@chelsea-pensioners.org.uk