The summer blockbuster film Oppenheimer has given millions a fresh understanding of how and why America raced to develop atom bombs, ultimately bringing an end to World War Two.

Director Christopher Nolan’s epic concentrates on the turbulent life of theoretical physicist J. Robert Oppenheimer, played brilliantly by Peaky Blinders star Cillian Murphy. Oppenheimer was head of the Los Alamos Laboratory in New Mexico where the world’s first atomic bomb was successfully tested in July 1945.

“Now I am become Death, the destroyer of worlds,” he is supposed to have said ­on realising the weapon’s Earth-shattering potential, quoting the Hindu scripture, the Bhagavad Gita.

On today’s date in August 1945, the world witnessed for a second time the destructive power of Oppenheimer’s bombs when they flattened a large part of Nagasaki, three days after most of Hiroshima had been destroyed by the first.

Up to 226,000 people were killed, mainly civilians. To this day, the bombings remain the only use of nuclear weapons in ­armed conflict.

Now a new book, focusing on the key ­military and political figures in the conflict between the US and Japan, paints a disturbing picture of how close America came to dropping a third atomic bomb. Some leaders in Japan had vowed never to surrender, even if it meant sacrificing 100 million lives.

American author Evan Thomas, 72, a ­former journalist, has examined diaries from those in the eye of the storm for his brilliant but discomfiting book, Road To Surrender. And he reveals that the disagreements behind the scenes were not only on the Japanese side.

Initially, US President Harry Truman left a lot of the detailed planning of the bomb drops to his elderly war secretary Henry Stimson, who was struggling to sleep properly, suffering from exhaustion and a weakened heart. Publicly Truman and Stimson ­
got on well, but privately they had a strained relationship.

“Stimson did not like the US incendiary bombings of Tokyo in March 1945 which killed 85,000 in firestorms,” says Thomas.

Stimson, a Republican, viewed Truman, a Democrat who took over as President following the death of Franklin D Roosevelt, as a nuisance and untrustworthy. At one point Stimson told Truman: “I do not want the US to get the reputation of outdoing Hitler in atrocities.” As Thomas explains, the weapons of mass destruction “offended his Christian sensibilities”.

Truman appreciated the magnitude of what the US was about to do but seemed unaware of the true power of the bomb and the indiscriminate nature of the killing it would inflict.

He wrote in his diary: “I have told Mr Stimson to use it so that military objectives and soldiers and sailors are the target and not women and children.Even if the Japs are savages, ruthless, merciless and fanatic, we as the leader of the world for the common welfare cannot drop this terrible bomb on the old capital or the new.”

He wrote that it was good that Hitler or Stalin did not have atomic weapons, adding: “It seems to be the most terrible thing ever discovered, but it can be made useful.”

But his belief that only Japanese combatants would be targeted were woefully misplaced.

Oppenheimer himself had predicted the first five-ton bomb, called Little Boy, to be dropped on Hiroshima, would kill 20,000, but the initial blast killed 70,000 instantly with up to 70,000 more dying later from horrific radiation poisoning.

Thomas says: “Truman gave Stimson a lot of discretion but when he saw the pictures of the atomic bomb damage he took back control.”

When the guilt-ridden Oppenheimer told Truman months later he felt he had “blood on his hands”, the affronted President had the “cry-baby scientist” kicked out of the Oval Office.

As soon as the first bomb had been dropped on August 6, and bomber pilot Colonel Paul Tibbets had returned to the US base at Tinian Island in the Pacific, Washington’s smokescreen propaganda operation swung into action.

A Purple Heart medal was stuck on Tibbets’ chest and the world learnt the all-American hero had named the B-29 bomber after his mother, Enola Gay. But what the public weren’t told was that Tibbets had given his entire crew cyanide capsules to swallow in case they’d been forced to ground the bomber on enemy territory.

The public was also unaware how unpredictable Tibbets could be in high-pressure situations. During an earlier bombing mission over Europe, he was slightly injured during an attack by a German fighter plane. When a worried RAF man on board tried to take the controls of the aircraft, short-fused Tibbets elbowed him in the face and knocked him out.

When the second bomb, nicknamed Fat Man, was duly dropped on August 9, the operation became a chaotic mess.

To the horror of Major Charles Sweeney, the pilot of the B29 bomber called Bockscar which carried the device, a light flashed during the flight to show that Fat Man was already armed. The weapon had to be urgently re-wired by an on-board electrician to make it safe until it was ready to be released.

The actual target was the city of Kokura but Sweeney discovered it swathed in haze and smoke when he flew above it.

Meanwhile, a second B29 which was due to film the bombing was circling at 9,000 feet above Bockscar – far too high.

In the aerial confusion over who was where, a radio message was flashed to the base at Tinian suggesting that Bockscar might have to ditch with its atomic bomb on board. On hearing this, one US general vomited in shock.

Thomas explains: “The first atomic bomb mission was perfect but the second was a fiasco. It was a case of what can go wrong will go wrong.

“They wasted a lot of time circling around waiting for the photography plane and they were running low on fuel.”

They were also coming under fire from Japanese anti-aircraft weaponry and were forced to fly 45 minutes to find the secondary target, Nagasaki.

With so little time left, they dropped the bomb one mile off target, over a Mitsubishi industrial complex, killing 35,000 immediately. Many thousands more died a slow death from radiation.

Thomas says the crew of the bomber talked about ditching in the Pacific when they realised they didn’t have enough fuel to return to base. Instead, they landed at the recently conquered Japanese island of Okinawa with just 35 gallons of fuel left from the 7,000 gallons they set out with.

After the devastation, Truman said he alone would decide when a third atomic bomb should be dropped. It was due to arrive at the Pacific base around August 18 and Kokura was back on the target list.

As arguments raged in the US over the bombing strategy, the Japanese government was enduring its own internal battles. Of their six leaders directing the war, three were for surrendering and three were against.

“In that group of six, foreign minister Shigenori Togo was the only one who wasn’t crazy,” says Thomas. “Initially he was the only one who wanted to surrender but he could not persuade the naval and army chiefs.

“They knew they were defeated but they wanted to keep power and keep the imperial system in place.”

The prime minister, Kantaro Suzuki, was 77 and not in good health. Meanwhile the war minister, General Korechika Anami, wanted the country to fight to the death, claiming that if 100 million died it would be like “seeing cherry blossoms fall to the ground, a beautiful sight”. The twisted sentiment showed just how deranged he had become.

Thomas says at the same time, Japanese traitors were agitating for another member of the Emperor’s family to take control and tried to persuade Hirohito to move to a palace in the mountains, but he courageously refused to leave Tokyo.

Thankfully, on August 15, 1945 Hirohito made an historic radio broadcast which avoided using the word “surrender” but did concede that the war had developed “not necessarily to Japan’s advantage”. He added: “We have resolved to pave the way for a grand peace.”

After signing a surrender document on August 14, following a failed palace coup, General Anami committed suicide by disembowelment.

Thomas adds: “I hadn’t realised what a close run thing this whole endgame was until I got into it. We came close to dropping a third atom bomb.”

And there were discussions about dropping further US atomic bombs, possibly as many as five more, between September and Christmas 1945 if Japan chose not to surrender.

Although Thomas of course hopes nuclear weapons will never be used again, he worries that in future years the US may get embroiled in a “limited nuclear exchange” with China.

As a former Washington bureau chief for Newsweek magazine and a journalism lecturer at Harvard and Princeton universities, his predictions should be taken seriously.

Since that fateful week in August 1945, the world has fortunately never seen nuclear weapons used again in war, but history teaches us that in an unstable world – Russia has already threatened to use nuclear weapons against Ukraine – such a scenario is possible.

This sobering book not only reminds us of the tragedy of the Japan bombings, it also exposes the frightening speed at which chaos can engulf a government with its fingers on the nuclear button.

• Road to Surrender by Evan Thomas (Elliott & Thompson Limited, £20) is available to order from Express Bookshop. Visit expressbookshop.com or call on 020 3176 3832