45

The mushroom cloud

In a remote part of the New Mexico desert, the United States government had tested a powerful new weapon on 16 July. The atomic bomb, as it was called, exploited recent breakthroughs in theoretical physics to cause a nuclear chain reaction. It was far more powerful than any other weapon in existence — a single one of these bombs could devastate a city. The secret project to develop such a bomb, the Manhattan Project, had been given priority in part because the Allies believed that the two major Axis powers, Germany and Japan, were conducting research into atomic bombs themselves. It later turned out that this was true, but that the atomic-research projects of the Axis nations had stalled and were far behind that of the United States.

The massive, devastating explosion caused by the atomic bomb produced a column in the air with a high-altitude bloom that bore a passing resemblance to a mushroom. This formation became known as a ‘mushroom cloud’.

The United States president, Harry S. Truman, did not tell General MacArthur, who was busy making planes for the Kyushu invasion, or other military leaders, about the New Mexico test or even about the existence of the two bombs.

Nor did he tell them that he and his civilian military advisers were intent on using the bomb to end the war as quickly as possible. The strategists in Washington wanted to choose a location that would have maximum effect, to force Japan to surrender. They wanted to cause both a massive loss of civilian life as well as heavy military disruption.1 They wanted to demoralise the Japanese people.

Many factors went into the decision about the bomb’s first target, some of them arbitrary — including the site’s military value, whether there was reliable enough weather for the project to go ahead, and whether it contained a large-enough population hub.

Hiroshima and a handful of other cities were shortlisted. In terms of military value, one of the factors that made Hiroshima attractive to the strategists was that it was a troop-transportation hub. As one Japanese report said, ‘Probably more than a thousand times since the beginning of the war did the Hiroshima citizens see off with cries of “Banzai” the troops leaving from the harbor.’2

Hiroshima’s role as a water-transport hub had become clear ever since the breaking of the Water Transport code at Central Bureau, Brisbane, two years earlier. Decrypted messages, and above all comprehensive traffic analysis of the code, pointed time and time again to the location of water-transport headquarters in the Japanese city of Hiroshima. And so Hiroshima was chosen as the target.

General MacArthur and Admiral Nimitz were only informed two days before the bomb was to be dropped, and after the decision to do so had already been made.3

When they were told of the plan, the military leaders were horrified. MacArthur, Nimitz, and other military commanders advised the president not to use the weapon, but Truman had made up his mind.

The key components of the bomb were shipped from the west coast of the United States to Tinian Island aboard the United States cruiser USS Indianapolis. On the cruiser’s return journey, a Japanese submarine torpedoed the Indianapolis and sunk it; almost the entire crew of 1200 drowned.4

On 6 August 1945, a bomber named the Enola Gay left North Field, an airstrip on the tiny island of Tinian, one of the Mariana Islands, about 2500 km east of the Philippines in the Pacific Ocean. It flew six hours straight to Hiroshima, where it dropped a single bomb directly above the city.

To coincide with the Enola Gay’s journey, several wireless intercept sites in the Philippines, including Australian wireless units, were instructed to monitor Japanese air-to-ground traffic. They were alert for Japanese reconnaissance planes discovering the approach of the Enola Gay, in which case the aircraft would turn around and abandon its mission. Nobby Clarke, head of the air-to-ground solution section on Leyte, coordinated the activity. No such intercept was heard, and the Enola Gay reached the skies above Hiroshima without incident.

The atomic bomb, named ‘Little Boy’, detonated about 800 metres above the city with a devastating sonic boom, and caused a tall column to rise into the stratosphere, where it blossomed out into a wide, symmetric cloud. The bomb killed about 80,000 people, most of them instantly.

At San Miguel, Kana operators noticed that certain frequencies of Japanese radio traffic, usually buzzing with messages, suddenly fell silent. Then, after a lull, they resumed, with a flurry of urgent messages about the bomb that had been dropped on Hiroshima.5

The interceptors received numerous messages describing the details of the bomb.6 What soon became clear was that the military were trying to figure out how to defend against it. They discovered from eyewitness reports that the bomb had been dropped by parachute, which suggested that a defence against it might involve firing at parachuted objects. For example:

Imperial headquarters is investigating a new type bomb used by the enemy (Atomic bomb) and devising counter measures against it. Since this type bomb is dropped by parachute, each group will immediately issue orders to have the anti aircraft guns fire on all bombs dropped by parachute.7

The following day, 7 August, a statement was issued by President Truman, announcing that the United States had detonated an atomic bomb over Hiroshima. Detailing the long period of its development and the massive expenditure of resources it had involved, he described the new weapon as harnessing ‘the basic power of the universe’, saying, ‘The force from which the sun draws its power has been loosed against those who brought war to the Far East.’ Truman threatened to drop further bombs if there was no peace.

On 8 August, the Japanese foreign minister, Shigenori Tōgō, met with the emperor of Japan, Hirohito, and told him it was time to surrender.

The dropping of the bomb on Hiroshima stirred Russia’s leader, Joseph Stalin, into action. He was planning to join the war against Japan, but was now concerned that a peace deal was imminent and that Russia would be excluded from it. The Russian ambassador informed Hirohito that their nations were now at war. Russian forces immediately launched an attack on Manchuria.

On 9 August, the Japanese Supreme War Leadership Council held a crisis meeting to discuss the new developments: the new type of bomb, and Russia’s declaration of war. There was furious argument about whether Japan should surrender. While they argued, a second bomb was dropped on the smaller Japanese port city of Nagasaki. A second mushroom cloud ballooned into the sky above Japan, killing a further 45,000 people. This bomb, ‘Fat Man’, had been scheduled to be dropped on 11 August in the event that the Japanese did not surrender, but inclement weather was threatening the operation, so Truman had ordered it to be dropped two days early.

Despite the reality of atomic warfare and a new war with Russia, the leadership council failed to reach a consensus. The war minister and the heads of the Japanese army and navy were opposed to any surrender. They were planning to wait for the Allies to try to invade, so that they could fight a decisive battle on the homeland.8 The military leaders would agree to peace terms only under strict conditions, the central pillars of which were no occupation of Japan; Japanese control of disarmament; and Japanese control of any war-crimes trials. The conditions they had in mind effectively amounted to a truce rather than a surrender. Prime Minister Kantarō Suzuki left the meeting and met with his cabinet. At this meeting, too, no consensus emerged about a peace deal.9

Suzuki confronted Hirohito, telling him that Japan’s political and military leaders were deadlocked, and that he, the emperor, would have to choose a course of action.

A Japanese offer to accept the Potsdam terms was made on 11 August via Switzerland, although an amendment was inserted that preserved the ‘prerogatives of His Majesty as a sovereign ruler’. The wording was the result of a bureaucratic tussle within Japan over the precise crafting of the peace offer. President Truman rejected it. Given that Japan had no real bargaining power left, modifications to the agreement at this point were out of the question. On 14 August, Hirohito sent a message through Swiss diplomats, who were acting as intermediaries, that he would unconditionally accept the terms of the Potsdam Agreement.