Some few years before his death in 1995, Dr Aidan MacCarthy, a proud son of the Beara peninsula, mused upon his extraordinary experiences in the second World War. Given the endless pressures placed upon his frame, he must have suffered physical and psychological traumas in later life.

“No. I was very, very lucky,” he said. “I got skin cancer from the radiation of the atomic bomb and I got leukaemia from being close to the bomb and I had 16 operations in my arm as a result of the beatings. Obviously, I had the stroke and brain haemorrhage. But apart from that, nothing really.”

The quote is paraphrased by Gary Lennon, director of A Doctor's Sword, a documentary that somehow manages to make the unbelievable seem possible. Raised in Castletownbere, educated at Clongowes Wood, MacCarthy decided to join the British services after failing to find work as a doctor in Ireland.

“He was out with a few graduates in 1939 and they realised all the armed services were recruiting,” Lennon says. “They just pulled a waitress over and got her to flip a coin between army and air force and it landed on the air force. That’s how he decided.”

The sequence of adventures that followed would defy the credulity of audiences for a work of fiction. MacCarthy was among those evacuated at the miracle of Dunkirk. A year later, he was awarded the George Medal for rescuing the crew of a bomber that crashed at an RAF base in Suffolk. Having endured one famous British defeat, he lived through another when he was captured following the fall of Singapore in 1942.

The suffering of the Allied prisoners captured by the Japanese has been well documented. MacCarthy called upon his training as a physician to assist his comrades through the beatings and starvation. Able to spot beriberi when he saw it, he improvised ways of insinuating vitamin B into the meagre diet.

Later, while being transported from Java to Japan, his troop ship was torpedoed by the Americans. Following rescue by a Japanese destroyer, the prisoners were beaten mercilessly by an unsympathetic crew.

Eventually, after leaping overboard and ending up on a whaler, they were brought to their original doomed destination.

“Dunkirk? Fall of Singapore? Torpedoed by the Americans?” Lennon marvels. “He must have thought that nothing worse could happen. Then he ends up in Nagasaki. The phrase ‘stranger than fiction’ doesn’t really cover it.”

Snippets of the legend

And the story was far from over. The seeds of the film were sewn when Bob Jackson, its eventual producer, began hearing snippets of the legend in and around Castletownbere.

It was said that the surviving family had a Japanese sword that had been given to MacCarthy by his final commandant. Fourteen years ago, Jackson walked into the famous MacCarthy’s bar in that town.

“He looked around and said: ‘What’s this about a samurai sword?’” Lennon explains.

“And the woman behind the bar said: ‘You mean this sword?’ And that was Aiden’s daughter Adrienne. They struck up a friendship. That was the genesis.”

Some years later, Jackson and Lennon set about knocking the film into production. It was a difficult project to finance and, given the complexity of the story, a difficult one to structure. Some sort of order imposed itself when Nicola, another daughter, eventually tracked down a photograph that had accompanied the sword. The notes on the back added almost as much mystery as they dissipated. “Dear friend Dr MacCathy [SIC], I give it to you with the farewell present,” it read.

“It was in some ways the final piece of the puzzle,” Lennon says. “We had a picture of the man who gave it to him. We had a picture of the sword.’ But the sword has extraordinary significance in Japanese culture.”

What could MacCarthy have done to trigger such gratitude in a proud antagonist?

Working to a tight schedule, they eventually disentangled the story and tracked down the family of the original owner of the sword.

Following the detonation of the atomic bomb on Nagasaki, MacCarthy, who had been working in the city’s Mitsubishi plant, emerged to a localised apocalypse. He did his best to help the survivors before being transported to a work camp several miles from the city. It now seems that, as liberation loomed, MacCarthy stepped in to stop his fellow prisoners from attacking Lieut Isao Kusuno, who was in charge of the camp.

The war is a taboo

“There had been conflicting stories,” Lennon says. “The daughters had heard that, after the surrender, all the Aussie prisoners wanted to lynch him. It’s not an unreasonable feeling to have. Nicky had heard that story. It was challenging as well because Japanese culture doesn’t talk about these things. The war is a taboo.”

With this in mind, it was all the more remarkable that Lennon eventually managed to get the Kusuno family on screen and that they were so warm and communicative about their ancestor’s story.

“They met us right away and our ‘fixer’ said that sort of thing doesn’t happen in Japan,” he says. “The Japanese are so organised down to every second. Their reaction was so different to everybody else we’d met.”

MacCarthy went on to marry and live a busy life in England. The film packs staggering amounts of tragedy into a small space. But it ends in an impressively positive place. Read that phrase again. “I was very, very lucky,” the doctor later said.

“Yes, whenever he had a bad day we’d play that clip,” Lennon says. “And my editor remarked that, when she heard it, she realised she could never complain about anything in her life again.”

A Doctor's Sword is out on limited release from August 7th