Annapolis, Maryland:  John McCain was on his 23rd bombing mission over Vietnam on October 26, 1967 when, as he puts it now, he "stopped a missile with my aircraft".

Shot down, he plunged into a lake, was dragged out and set upon by a mob, which left him with three broken limbs. His captors threw him into the notorious Hanoi Hilton prison, tortured him, and left him to die in a cell with two other Americans, including the US Air Force's most decorated officer, Colonel Bud Gray.

But McCain was made of sterner stuff and now, in a series of interviews with The Sunday Telegraph, his closest friends from that dark time have spoken of the courage of the man who would be president, explaining how his experience in Vietnam made him, in their view, the candidate now best-suited to lead the United States.

"He was badly injured. He had two broken legs, a broken arm and had been bayoneted when he was dragged up on the shore of that lake. He was close to death," said Orson Swindle, who was to share a cell with McCain for three years.

Military record

Last week as the successful Republican nominee, he embarked on a five-state trip to old haunts and army bases where he had been stationed, highlighting his military record for the voters, who, polls show, favour him by up to 10 points over his Democratic rivals.

Yet, while even the most casual observer of American politics knows that McCain is a "war hero", many remain unaware of the full horror of his incarceration - and of the selfless decision that was the defining moment of his life.

It came nine months into his captivity, when the Vietnamese told McCain he could go home. The Communist authorities had learned that the young serviceman, who had been born into a distinguished American military family, was the son of the serving commander of American forces in the Pacific, and were willing to offer his release as part of a propaganda coup showing goodwill on their part. McCain, however, refused the offer, telling his captors he would only go if everyone taken before him were released, too.

"He told the toughest interrogator we had to 'Shove it!' Just those words," said Paul Galanti, who spent more than six years imprisoned in Hanoi. "The commander of all the camps, who spoke very good English, very refined, came and said: 'McCain, you will regret that decision.' They re-broke at least one of his bones.

"We knew he was horribly banged up and hurting. He was in such critical shape most of his time in captivity, he probably could have justified coming home but he wouldn't do it."

Instead, McCain ended up serving 5 1/2 years behind bars. As a Hanoi Hilton "celebrity", he was singled out for special treatment, leaving lasting injuries that to this day prevent him lifting his arms above shoulder height.

Jackie Fellowes, who spent three years in a cell with McCain and Swindle, said: "John knew the rules: first in, first out. We appreciated it."

Galanti said other people were also offered the chance of early release. "Some people took it. They can't be members of our group now," he said.

Swindle believes that his friend showed political judgment as well as personal courage. "For him to have accepted release would have been a propaganda coup for the Communists. He wasn't about to let that happen, no matter if it cost him his life and it could have."

McCain began his biography tour last week with a speech outlining his family's history of military service. One ancestor served with George Washington, and both his father and grandfather became four-star admirals.

McCain's comrades-in-arms believe that it was in Hanoi that he realised the depth of his desire to serve his country, an ambition that drove him to the House of Representatives in 1982, two years after he had left the Navy, and then to the Senate.

Fellowes said: "We had days when things weren't going so well. John would have a joke. Even a terrible joke was funny. His spirit kept all of our spirits high. I'd wake up feeling terrible and see him smile. I'd say: 'How can I feel terrible when I see you smile.'?"

- The Telegraph Group Limited, London 2008