Was the USA right to drop an atomic bomb on Hiroshima 80 years ago? Most people think so, even though they also realise that the attack killed many innocent civilians, often in quite horrible ways which it is hard to face.

Do they excuse those gruesome horrors of burned human flesh and radiation sickness because they simply can’t bear to consider the possibility that it was both a major mistake and a moral crime?

My father, who was a serving naval officer in European waters at the time, was among thousands of British sailors, soldiers and airmen who would say confidently that the bomb probably saved his life, as he expected to be sent to the Pacific for a merciless final struggle against Japan. And, like most at the time, he believed that the Japanese would put up a suicidal last-ditch resistance when British and American forces landed on their home islands.

He was not sorry to have been spared this fate. He’d had quite enough to do, fighting against Germany for the previous six years.

For the rest of his life (he died in 1987) this was a perfectly respectable belief. The accepted view was that the Japanese would have carried on fighting to the death, inch by inch.

When the US Army and US Marines, supported by British and Commonwealth forces, invaded the Japanese island of Okinawa in 1945, they faced resistance bordering on the insane, and often actually suicidal. There were hundreds of kamikaze attacks. Allied casualties totalled 50,000, more than 12,500 killed. The Japanese lost more than 100,000 soldiers and sailors, most of them killed. Perhaps 150,000 civilians died.

The battle came to be known as ‘The Typhoon of Steel’. If that was what happened on one small island, what would it be like when the Allies landed on the mainland?

But then along came Japanese-American historian, Tsuyoshi Hasegawa. Professor Hasegawa, born in Japan in 1941 but now a US citizen, is also a Russian speaker and expert on that country. In 2005 he published a book Racing The Enemy: Stalin, Truman, And The Surrender Of Japan which upset everything most people had until then believed.

The so-called mushroom cloud of the atomic bomb on Hiroshima on August 6, 1945 

His view, after careful study of Japanese and Soviet archives, is that Tokyo surrendered not because of the Hiroshima bomb, or the Nagasaki bomb three days later, but because the Soviet Union had finally entered the war against Japan on the Allied side.

The Japanese leadership of the time were ruthless, ferocious men who cared little about civilian casualties (or military casualties for that matter). They had been untroubled by the American bombing of Tokyo in March 1945, the single most destructive air raid in human history.

That attack destroyed 16 square miles of the Japanese capital and killed at least 100,000 people. Nearly 300 bombers dropped nearly 1,700 tons of bombs on the city, including napalm and white phosphorus, two of the most merciless weapons of war known to man.

When the fires eventually died down the devastated streets were full of charred human corpses. Only 27 US planes were lost. Yet the Japanese made no move to surrender.

But the Japanese were afraid of Stalin. In a wrongly forgotten 1936-1939 war, the Red Army had decisively beaten the Japanese Sixth Army, finishing the job with a thumping victory at Nomonhan on the border of Mongolia and China. Japan also feared Russia’s ability to enter Japanese territory by land, via the disputed island of Sakhalin, which was then divided between Moscow and Tokyo.

Both countries had maintained a mad-seeming neutrality pact since 1941, in which they had agreed not to attack each other, even though they belonged to hostile alliances which were at each other’s throats. They ought to have been at war.

But at the Yalta conference of February 1945, Stalin had secretly promised US President Franklin Roosevelt and Britain’s Winston Churchill that he would break the pact within three months of victory over Germany.

The city of Hiroshima before and after the bomb was detonated. The explosion killed around 140,000 people and was followed by the bombing of Nagasaki on August 9

Survivors of the Hiroshima bomb pictured in a Japanese hospital in 1945, suffering from the effects of radiation

He kept his word. Three days after the Hiroshima bomb, while the US was bombing Nagasaki, 1.6 million Soviet troops attacked Japanese forces all across North-East Asia, quickly capturing the southern half of Sakhalin and so positioning themselves perfectly for an assault on the Japanese home islands, less than 30 miles away.

They also seized the Kuril islands, a land-grab the Japanese dispute to this day. It was a real and immediate threat with no good outcome for Japan.

Japan’s ruthless military dictatorship may well have viewed this development as a threat to the actual existence of their country. A Soviet Communist occupation regime certainly would not have allowed Emperor Hirohito to remain on his throne, even if he had no power – an arrangement eventually agreed to by the chief of the US occupying troops, General Douglas MacArthur.

Russia, having been humiliated in a war with Japan in 1904, was a dangerous and greedy neighbour that might well keep any territory it took. Russian armies were much less likely than American forces to leave once they arrived.

Professor Hasegawa, who went deep into both Soviet and Japanese archives, concluded that the Russian threat was much more likely than the atom bombs to have triggered the Japanese surrender of August 15.

Addressing the military at the time of the surrender, Emperor Hirohito did not mention the A-bombs but did mention the Soviet threat. Yet, when speaking to the Japanese people, he mentioned the ‘new and cruel’ weapons that had been used against Hiroshima and Nagasaki.

There is no final tribunal that can decide for certain why Japan surrendered when it did, or whether it was Stalin or the atom bomb, which clinched the decision. But Hasegawa certainly makes a persuasive and worrying case.

Hasegawa’s view would have been a deep and dangerous heresy until quite recently when the main arguments were over whether the A-bomb should have been used at all.

Before the end of the Cold War, nuclear disarmers would often claim that the newly installed US President Harry Truman – an undistinguished machine politician from Missouri who had been lifted suddenly into the White House by the death of Roosevelt – had dropped the bombs to impress Stalin with America’s overwhelming new power. Perhaps there is some truth in this, too.

But a very perplexing question remains, to which we can probably never find the answer. Would the world be a better place if the atomic bomb had never been invented?

Albert Einstein thought one of his greatest mistakes was to encourage Roosevelt to build the bomb in 1939. The Italian physicist Ettore Majorana, rated as a genius by his scientific fellows, disappeared from the face of the earth in 1938, aged 31. Many believe he deliberately vanished and hid himself in a South American jungle as he’d foreseen that his researches would lead to the atom bomb, and he could not bear to be responsible for it.

Some of the British scientists who had helped build the bomb because they feared Hitler might make one first were grieved to see it used against Japan – and even more so when they discovered, thanks to a brilliant British intelligence coup – that Hitler’s physicists never got anywhere near a working nuclear device.

As war erupts in Ukraine and Iran like an evil disease, the argument that nuclear deterrence would bring peace looks a little threadbare. Long ago, we learned to stop worrying and love the Bomb because we thought it was a force for peace. Maybe we should start worrying again.