He was traveling across Hiroshima on a public tram when he heard the droning sound of an aircraft engine in the skies above.

Tsutomu Yamaguchi thought nothing of it. After all, it was wartime and planes were forever passing above the city. He was unaware that the engines belonged to the U.S. bomber Enola Gay, and that it was just seconds away from dropping a 13 kiloton uranium atomic bomb on the city.

As the plane approached its target at 8:15 a.m. on Aug. 6, 1945, Yamaguchi had just stepped off the tram. He glanced at the sky and noticed a bomber passing overheard. He also saw two small parachutes. And then, quite without warning, all hell broke loose.

“[There was] a great flash in the sky and I was blown over.” The massive nuclear warhead had exploded less than three kilometers from the spot where he was standing.

The bomb was detonated at 600 meters above Hiroshima. As Yamaguchi swung his gaze upwards, he saw a vast mushroom-shaped pillar of fire rising high into the sky. Seconds later, he passed out. The blast caused his eardrums to rupture and the flash of light left him temporarily blinded.

The heat of the explosion was such that it left him with serious burns over the left side of his body. When he eventually regained consciousness, he crawled to a shelter and tried to make sense of what had happened. Fortunately, he stumbled across three colleagues who had also survived. All were young engineers working for the shipbuilder Mitsubishi Heavy Industries. They had been unlucky enough to be sent to Hiroshima on the very day of the bombing.

They spent the night together in an air-raid shelter, nursing their burns and wounds. Then, on the following morning, they ventured out of their shelter and picked their way through the charred and molten ruins. As they went to the nearest functioning railway station they passed piles of burnt and dying bodies. Their aim was to catch one of the few working trains back to their hometown of Nagasaki, some 200 miles away.

Yamaguchi was in a poor state and went to have his wounds bandaged as soon as he reached Nagasaki. But by Aug. 9, after just two days of convalescence, he felt well enough to struggle into work.

His boss and his co-workers listened in horrified amazement as he described the unbelievable destruction that a single bomb had managed to cause. He told them how the explosion had melted metal and evaporated entire parts of the city. His boss, Sam, simply didn’t believe him.

“You’re an engineer,” he barked. “Calculate it. How could one bomb destroy a whole city?”

At the exact moment he said these words—11:02 a.m.—there was a blinding white flash that penetrated to the heart of the room. Yamaguchi’s tender skin was once again pricked with heat and he crashed to the ground. “I thought that the mushroom cloud followed me from Hiroshima,” he said later.

The U.S. Air Force had dropped their second nuclear warhead—Fat Man—named after Winston Churchill. It was much larger than the Hiroshima device, a 25 kiloton plutonium bomb that exploded in the bowl of the valley where Nagasaki is situated.

The destruction was more confined but even more intense than at Hiroshima. Some 74,000 were killed and a similar number injured.

Yamaguchi, his wife, and his baby son managed to survive and spent much of the following week in an air-raid shelter near what was left of their home. Five days later, they heard the news that Emperor Hirohito had announced Japan’s surrender.

Yamaguchi’s survival of both nuclear explosions was little short of miraculous. Yet it was later discovered that he was one of 160 people known to have lived through both bombings.

In 1957, he was recognized as a hibakusha or “explosion-affected person.” But it was not until 2009 that he was officially allowed to describe himself as an eniijuu hibakusha or double bomb survivor.

The effects of the double bombings left its scars, both mental and physical. Yamaguchi lost the hearing in his left ear as a result of the Hiroshima explosion. He also lost his hair temporarily. His daughter would later recall that he was swathed in bandages until she reached the age of 12.

Yamaguchi became an outspoken opponent of nuclear weapons until he was well advanced in years, at which point he began to suffer from the long-term effects of the exposure to radiation. His wife developed liver and kidney cancer in 2008 and died soon after. Yamaguchi himself developed acute leukemia and died in 2010 at the age of 93. His longevity was extraordinary, as he knew only too well. He viewed his long life as a “path planted by God.”

“It was my destiny that I experienced this twice and I am still alive to convey what happened,” he said towards the end of his life.

This article is excerpted from Giles Milton’s When Hitler Took Cocaine and Lenin Lost His Brain: History’s Unknown Chapters and is reprinted with the permission of the publisher, Picador.