WWII Atomic Bombs:


Before Germany Surrendered:

Even before the surrender of Nazi Germany on the 8th May 1945, plans were already underway for the largest operation of the Pacific War, 'Operation Downfall', the invasion of Japan; the operation had two parts 'Olympic' and 'Coronet'; 'Olympic' set to begin in October 1945, involved a series of landings by the U.S. Sixth Army intended to capture the southern third of the southernmost main Japanese island, Kyushu.

Operation Olympic was to be followed in March 1946 by Operation Coronet, the capture of the Kanto Plain, near Tokyo on the Japanese island of Honshu by the U.S. First, Eighth and Tenth Armies; the target date was chosen to allow for Olympic to complete its objectives, troops to be redeployed from Europe and the Japanese winter to pass.

Japanese Awareness:

Unfortunately, Japan's geography made this invasion plan obvious to the Japanese as well; they were able to predict the Allied invasion plans accurately and thus adjust their defensive plan, 'Operation Ketsugo', accordingly; the Japanese planned an all out defense of Kyushu, with little left in reserve for any subsequent defense operations.

Four veteran divisions were withdrawn from the Kwantung Army in Manchuria in March 1945 to strengthen the forces in Japan and 45 new divisions were activated between February and May 1945; most were immobile formations for coastal defence, but 16 were high quality mobile divisions; in all, there were 2.3 million Japanese Army troops prepared to defend the Japanese home islands, another 4 million Army and Navy employees and a civilian militia of 28 million men and women.

Casualty predictions varied widely, but were extremely high; the Vice Chief of the Imperial Japanese Navy General Staff, Vice Admiral Takijiro Onishi, predicted up to 20 million Japanese deaths; the Americans were alarmed by the Japanese build up, which was accurately tracked through Ultra intelligence.

The USA Concern Over Estimated Casualties:

The USA Secretary of War Henry Lewis Stimson was sufficiently concerned about high American estimates of probable casualties to commission his own study by Quincy Wright and William Shockley; Wright and Shockley spoke with Colonels James McCormack and Dean Rusk and examined casualty forecasts by Michael DeBakey and Gilbert Beebe; Wright and Shockley estimated the invading Allies would suffer between 1.7 and 4 million casualties in such a scenario, of whom between 400,000 and 800,000 would be dead, whilst Japanese casualties would have been around 5 to 10 million.

The Offensive:

The Chief of Staff of the US Army and the General of the Army George C. Marshall began contemplating the use of a weapon which was "readily available and which assuredly can decrease the cost in American lives"; poison gas; quantities of phosgene, mustard gas, tear gas and cyanogen chloride were moved to Luzon from stockpiles in Australia and New Guinea in preparation for Operation Olympic and the General of the Army Douglas MacArthur ensured that Chemical Warfare Service units were trained in their use.

Whilst the USA had developed plans for an air campaign against Japan prior to the Pacific War, the capture of Allied bases in the western Pacific in the first weeks of the conflict meant that this offensive did not begin until mid 1944 when the long ranged Boeing B-29 Superfortress became ready for use in combat.

Operation 'Matterhorn' involved India based B-29s staging through bases around Chengtu in China to make a series of raids on strategic targets in Japan between June 1944 and January 1945; this effort proved unsuccessful due to logistical difficulties with the remote location, technical problems with the new and advanced aircraft, unfavourable weather conditions and ultimately enemy action.

USAAF Brigadier General Haywood S. Hansell determined that Guam, Tinian and Saipan in the Mariana Islands would better serve as B-29 bases, but they were in Japanese hands; strategies were shifted to accommodate the air war and the islands were captured between June and August 1944; air bases were developed and B-29 operations commenced from the Marianas in November 1944, greatly expanding the scope of the strategic bombing campaign against Japan.

These attacks initially targeted key industrial facilities, but from March 1945 they were frequently directed against urban areas; the capture of Okinawa in June 1945 provided airfields even closer to the Japanese mainland, allowing the bombing campaign to be escalated further; over the next six months, the XXI Bomber Command fire bombed 67 Japanese cities; the 9 to 10 March Bombing of Tokyo alone caused 80,000 to 100,000 casualties and destroyed around 16 square miles (41 km2) of the city with 267,000 buildings, the deadliest of the war.

Aircraft flying from Allied aircraft carriers and the Ryukyu Islands also regularly struck targets in Japan during 1945 in preparation for Operation Downfall; the Japanese military was unable to stop the Allied attacks and the country's civil defense preparations proved inadequate; from April 1945, the Japanese Army and Naval Air Forces stopped attempting to intercept the air raids in order to preserve fighter aircraft to counter the expected invasion.

By mid 1945 the Japanese also only occasionally scrambled aircraft to intercept individual B-29s conducting reconnaissance sorties over the country in order to conserve supplies of fuel; by July 1945, the Japanese had stockpiled 1,156,000 US barrels of avgas for the invasion of Japan.

The Manhattan Project:

Working in collaboration with the UK and Canada, with their respective projects Tube Alloys and Chalk River Laboratories, the Manhattan Project, under the direction of Major General Leslie Groves, of the U.S. Army Corps of Engineers, designed and built the first atomic bombs; preliminary research began in 1939, originally in fear that the Nazi atomic bomb project would develop atomic weapons first.

In May 1945, the defeat of Germany caused the focus to turn to use against Japan; two types of bombs were eventually devised by scientists and technicians at Los Alamos under American physicist Robert Oppenheimer, a 'Little Boy' type and a 'Fat Man' type.

The Targets:

The USA Target Committee originally nominated four targets; Kokura, the site of one of Japan's largest munitions plants; Hiroshima, an embarkation port and industrial center that was the site of a major military headquarters; Niigata, a port with industrial facilities including steel and aluminium plants and an oil refinery; and Kyoto, a major industrial center.

The target selection was subject to the following criteria:
The target was larger than 3 miles (4.8 km) in diameter and was an important target in a large urban area.
The blast would create effective damage.
The target was unlikely to be attacked by August 1945, "Any small and strictly military objective should be located in a much larger area subject to blast damage in order to avoid undue risks of the weapon being lost due to bad placing of the bomb."

These cities were largely untouched during the nightly bombing raids and the Army Air Force agreed to leave them off the target list so accurate assessment of the weapon could be made; Hiroshima was described as "an important army depot and port of embarkation in the middle of an urban industrial area. It is a good radar target and it is such a size that a large part of the city could be extensively damaged. There are adjacent hills which are likely to produce a focusing effect which would considerably increase the blast damage. Due to rivers it is not a good incendiary target."

The USA had previously dropped leaflets warning civilians of air raids on 35 Japanese cities, including Hiroshima and Nagasaki, but not of the atomic bomb as such; the goal of the weapon was to convince Japan to surrender unconditionally in accordance with the terms of the Potsdam Declaration.

The Target Committee stated that it was agreed that psychological factors in the target selection were of great importance; two aspects of this are, to obtain the greatest psychological effect against Japan and making the initial use sufficiently spectacular for the importance of the weapon to be internationally recognised when publicity on it is released.

Kyoto had the advantage of being an important center for military industry, as well an intellectual center and hence better able to appreciate the significance of the weapon; the Emperor's palace in Tokyo has a greater fame than any other target but is of least strategic value.

Edwin O. Reischauer a Japananese expert for the U.S. Army Intelligence Service, was incorrectly said to have prevented the bombing of Kyoto; in his autobiography, Reischauer specifically refuted this claim by stating that the only person deserving credit for saving Kyoto from destruction was Henry L. Stimson, the Secretary of War at the time, who had known and admired Kyoto ever since his honeymoon there several decades earlier and on the 25th July, Nagasaki was put on the target list in place of Kyoto.

Germany Surrenders - Japan Fights On Defiantly:

The war in Europe ended when Nazi Germany signed its instrument of surrender on the 8th May 1945, but the Pacific War continued; therefore, on the 26 July, the USA, together with the UK and the Republic of China issued the Potsdam Declaration outlining terms of surrender for Japan; it was presented as an ultimatum and stated that without a surrender, the Allies would attack Japan, resulting in "the inevitable and complete destruction of the Japanese armed forces and just as inevitably the utter devastation of the Japanese homeland"; however, the atomic bomb was not mentioned in the communiqué.

The Japanese government ignored this ultimatum and on the 28th July Japanese papers reported that the declaration had been rejected by the Japanese government; that afternoon, Prime Minister Kantaro Suzuki declared at a press conference that the Potsdam Declaration was no more than a rehash of the Cairo Declaration and that the government intended to ignore it (mokusatsu, "kill by silence"); the statement was taken by both Japanese and foreign papers as a clear rejection of the declaration; Emperor Hirohito, who was waiting for a Soviet reply to non committal Japanese peace feelers, made no move to change the government position.

Under the 1943 Quebec Agreement with the UK, the USA had agreed that nuclear weapons would not be used against another country without mutual consent; therefore in June 1945 the head of the British Joint Staff Mission, Field Marshal Sir Henry Maitland Wilson, agreed that the use of nuclear weapons against Japan would be officially recorded as a decision of the Combined Policy Committee.

At Potsdam, Truman agreed to a request from the Prime Minister of the UK, Winston Churchill, that Britain be represented when the atomic bomb was dropped; William Penney and Group Captain Leonard Cheshire were sent to Tinian, but found that Major General Curtis LeMay would not let them accompany the mission; all they could do was send a strongly worded signal back to Wilson.

The Hiroshima Bombing:

Hiroshima was the primary target of the first nuclear bombing mission on the 6th August, with Kokura and Nagasaki as alternative targets; the 393d Bombardment Squadron B-29 'Enola Gay', piloted by Tibbets, was launched from North Field airbase on Tinian, about six hours flight time from Japan.

The 'Enola Gay', named after Tibbets' mother, was accompanied by two other B-29s, 'the Great Artiste', commanded by Major Charles W. Sweeney, carried instrumentation and a then nameless aircraft later called 'Necessary Evil', commanded by Captain George Marquardt, served as the photography aircraft.

After leaving Tinian the aircraft made their way separately to Iwo Jima where they rendezvoused at 8,010 feet (2,440 meters) and set course for Japan; the aircraft arrived over the target in clear visibility at 32,333 feet (9,855 meters); Parsons, who was in command of the mission, armed the bomb during the flight to minimize the risks during takeoff; his assistant, Second Lieutenant Morris Jeppson, removed the safety devices 30 minutes before reaching the target area.

About an hour before the bombing, Japanese early warning radar detected the approach of some American aircraft headed for the southern part of Japan; an alert was given and radio broadcasting stopped in many cities, among them Hiroshima; at nearly 08:00, the radar operator in Hiroshima determined that the number of planes coming in was very small, probably not more than three, and the air raid alert was lifted.

To conserve fuel and aircraft, the Japanese had decided not to intercept small formations; the normal radio broadcast warning was given to the people that it might be advisable to go to air raid shelters if B-29s were actually sighted; however a reconnaissance mission was assumed because at 07:31 the first B29 to fly over Hiroshima at 32,000 feet (9,800 m) had been the weather observation aircraft 'Straight Flush' that sent a morse code message to the 'Enola Gay' indicating that the weather was good over the primary target.

Because it then turned out to sea, the 'all clear' was sounded in the city; at 08:09 Colonel Tibbets started his bomb run and handed control over to his bombardier; the release at 08:15, Hiroshima time, went as planned and the gravity bomb known as "Little Boy" took 43 seconds to fall from the aircraft flying at 31,060 feet (9,470 m) to the predetermined detonation height about 1,900 feet (580 m) above the city.

The 'Enola Gay' traveled 11.5 miles (18.5 km) before it felt the shock waves from the blast; due to crosswind, it missed the aiming point, the Aioi Bridge, by approximately 800 feet (240 m) and detonated directly over Shima Surgical Clinic; it created a blast equivalent to about 13 kilotons of TNT (54 TJ); the U-235 weapon was considered very inefficient, with only 1.38% of its material fissioning; the radius of total destruction was about one mile (1.6 km), with resulting fires across 4.4 square miles (11 km2).

The Americans estimated that 4.7 square miles (12 km2) of the city were destroyed; Japanese officials determined that 69% of Hiroshima's buildings were destroyed and another (6 to 7)% damaged; some 70,000 to 80,000 people, or some 30% of the population of Hiroshima were killed immediately and another 70,000 injured; over 90% of the doctors and 93% of the nurses in Hiroshima were killed or injured, most had been in the downtown area which received the greatest damage.

The Atomic Bomb That Was Dropped On Hiroshima:

On the 6th August 1945 a 'Little Boy' type, uranium-235 gun-type nuclear weapon was dropped on the city of Hiroshima; it was 28 inches in diameter and 120 inches long; it weighed about 9,000 pounds and had a yield approximating 15,000 tons of high explosives; it created a mushroom cloud which billowed up around 20,000 feet over Hiroshima.

Japanese realisation Of The Bombing:

The Tokyo control operator of the Broadcasting Corporation of Japan noticed that the Hiroshima station had gone off the air; he tried to re-establish his program by using another telephone line, but it too had failed; about 20 minutes later the Tokyo railroad telegraph center realised that the main line telegraph had stopped working just north of Hiroshima.

From some small railway stops within 9.9 mile (16 kilometres) of the city came unofficial and confused reports of a terrible explosion in Hiroshima; all these reports were transmitted to the headquarters of the Imperial Japanese Army General Staff; military bases repeatedly tried to call the Army Control Station in Hiroshima; the complete silence from that city puzzled the men at headquarters; they knew that no large enemy raid had occurred and that no sizeable store of explosives was in Hiroshima at that time.

A young officer of the Japanese General Staff was instructed to fly immediately to Hiroshima, to land, survey the damage and return to Tokyo with reliable information for the staff; it was generally felt at headquarters that nothing serious had taken place and that the explosion was just a rumor; the staff officer went to the airport and took off for the southwest; after flying for about three hours, while still nearly 99 miles (160 kilometres) from Hiroshima, he and his pilot saw a great cloud of smoke from the bomb; in the bright afternoon, the remains of Hiroshima were burning.

Their plane soon reached the city, around which they circled in disbelief; a great scar on the land still burning and covered by a heavy cloud of smoke was all that was left; they landed south of the city and the staff officer, after reporting to Tokyo, immediately began to organise relief measures; by the 8th August 1945, newspapers in the USA were reporting that broadcasts from Radio Tokyo had described the destruction observed in Hiroshima as "Practically all living things, human and animal, were literally seared to death."

Hiroshima Casualty Estimates:

Video footage taken in Hiroshima in March 1946 showed victims with severe burns; according to the U.S. Department of Energy the immediate effects of the blast killed approximately 70,000 people in Hiroshima; estimates of total deaths by the end of 1945 from burns, radiation and related disease, the effects of which were aggravated by a lack of medical resources, range from 90,000 to 166,000; some estimates state up to 200,000 had died by 1950, due to cancer and other long term effects; another study states that from 1950 to 2000, 46% of leukemia deaths and 11% of solid cancer deaths among bomb survivors were due to radiation from the bombs, the statistical excess being estimated to 94 leukemia and 848 solid cancers.

After Hiroshima:

After the Hiroshima bombing, Truman issued a statement announcing the use of the new weapon; he stated, "We may be grateful to Providence" that the German atomic bomb project had failed and that the USA and its allies had "spent two billion dollars on the greatest scientific gamble in history-and won."; Truman then warned Japan that if they do not now accept our terms, they may expect a rain of ruin from the air, the like of which has never been seen on this earth; behind this air attack will follow sea and land forces in such numbers and power as they have not yet seen and with the fighting skill of which they are already well aware.

Leaflets urging quick surrender were dropped over Japan by the 509th Composite Group, but the Japanese government still did not react to the Potsdam Declaration; Emperor Hirohito, the government and the war council were considering four conditions for surrender; the preservation of the kokutai, Imperial institution and national polity, assumption by the Imperial Headquarters of responsibility for disarmament and demobilisation, no occupation of the Japanese Home Islands, Korea, or Formosa, and delegation of the punishment of war criminals to the Japanese government.

The Soviet Foreign Minister Vyacheslav Molotov had informed Tokyo of the Soviet Union's unilateral abrogation of the Soviet–Japanese Neutrality Pact on the 5th April; at two minutes past midnight on the 9th August, Tokyo time, Soviet infantry, armour and air forces had launched the Manchurian Strategic Offensive Operation; 4 hours later, word reached Tokyo that the Soviet Union had declared war on Japan; the senior leadership of the Japanese Army began preparations to impose martial law on the nation, with the support of Minister of War Korechika Anami, in order to stop anyone attempting to make peace.

The Nagasaki Bombing:

Responsibility for the timing of the second bombing was delegated to Tibbets; scheduled for the 11th August against Kokura, the raid was moved forward by 2 days to avoid a 5 day period of bad weather forecast to begin on the 10th August; 3 bomb pre assemblies had been transported to Tinian, labeled F-31, F-32, and F-33 on their exteriors; on the 8th August, a dress rehearsal was conducted off Tinian by Sweeney using Bockscar as the drop airplane; assembly F-33 was expended testing the components and F-31 was designated for the 9th August mission.

On the morning of the 9th August 1945, the B-29 Superfortress 'Bockscar', flown by Sweeney's crew, carried Fat Man, with Kokura as the primary target and Nagasaki the secondary target; the mission plan for the second attack was nearly identical to that of the Hiroshima mission, with two B-29s flying an hour ahead as weather scouts and two additional B-29s in Sweeney's flight for instrumentation and photographic support of the mission.

Sweeney took off with his weapon already armed but with the electrical safety plugs still engaged; this time Penney and Cheshire were allowed to accompany the mission, flying as observers on the third plane, 'Big Stink', which was flown by the group's Operations Officer, Lieutenant Colonel James I. Hopkins, Jr. Observers aboard the weather planes reported both targets clear.

When Sweeney's aircraft arrived at the assembly point for his flight off the coast of Japan, 'Big Stink', failed to make the rendezvous; Bockscar and the instrumentation plane circled for 40 minutes without locating Hopkins; already 30 minutes behind schedule, Sweeney decided to fly on without Hopkins; by the time they reached Kokura a half hour later, a 70% cloud cover had obscured the city, prohibiting the visual attack required by orders.

After three runs over the city and with fuel running low because a transfer pump on a reserve tank had failed before take-off, they headed for their secondary target, Nagasaki; fuel consumption calculations made en route indicated that 'Bockscar' had insufficient fuel to reach Iwo Jima and would be forced to divert to Okinawa.

After initially deciding that if Nagasaki were obscured on their arrival the crew would carry the bomb to Okinawa and dispose of it in the ocean if necessary, the weaponeer, Navy Commander Frederick Ashworth, decided that a radar approach would be used if the target was obscured; at about 07:50, Japanese time, an air raid alert was sounded in Nagasaki, but the "all clear" signal was given at 08:30; when only two B-29 Superfortresses were sighted at 10:53, the Japanese apparently assumed that the planes were only on reconnaissance and no further alarm was given.

A few minutes later at 11:00, 'The Great Artiste', the support B-29 flown by Captain Frederick C. Bock, dropped instruments attached to three parachutes; these instruments also contained an unsigned letter to Professor Ryokichi Sagane, a nuclear physicist at the University of Tokyo who studied with three of the scientists responsible for the atomic bomb at the University of California, Berkeley, urging him to tell the public about the danger involved with these weapons of mass destruction.

The messages were found by military authorities but not turned over to Sagane until a month later; in 1949, one of the authors of the letter, Luis Alvarez, met with Sagane and signed the document; at 11:01, a last minute break in the clouds over Nagasaki allowed Bockscar's bombardier, Captain Kermit Beahan, to visually sight the target as ordered.

The Fat Man weapon, containing a core of about 14 lbs (6.4 kilograms) of Plutonium, was dropped over the city's industrial valley; it exploded 43 seconds later at 1,539 feet (469 metres) above the ground halfway between the Mitsubishi Steel and Arms Works in the south and the Mitsubishi-Urakami Ordnance Works, Torpedo Works, in the north.

This was nearly 1.9 miles (3 kilometres) northwest of the planned hypocenter; the blast was confined to the Urakami Valley and a major portion of the city was protected by the intervening hills; the resulting explosion had a blast yield equivalent to 21 kilotons of TNT (88 TJ); the explosion generated heat estimated at 3,900 °C (7,050 °F) and winds that were estimated at 624 mph (1,005 km/h).

Nagasaki Casualty Estimates:

Casualty estimates for immediate deaths range from 40,000 to 75,000; total deaths by the end of 1945 may have reached 80,000; at least eight known POWs died from the bombing and as many as 13 POWs may have died, including a British Commonwealth citizen, and seven Dutch POWs; one American POW, Joe Kieyoomia, was in Nagasaki at the time of the bombing but survived, reportedly having been shielded from the effects of the bomb by the concrete walls of his cell; the radius of total destruction was about 1 mile (1.6 km), followed by fires across the northern portion of the city to 2 miles (3.2 km) south of the bomb; the Mitsubishi-Urakami Ordnance Works, the factory that manufactured the type 91 torpedoes released in the attack on Pearl Harbor, was destroyed in the blast.

The Atomic Bomb That Was Dropped On Nagasaki:

On the 9th August 1945 a 'Fat Man' type, plutonium-239 implosion nuclear weapon was dropped on the city of Nagasaki; it was 60 inches in diameter and 128 inches long; it weighed about 10,000 pounds and had a yield approximating 21,000 tons of high explosives; it created a mushroom cloud which billowed up around 45,000 feet over Nagasaki.

Until the 9th August, the Japanese war council had still insisted on its four conditions for surrender; on that day Hirohito ordered Kido to "quickly control the situation ... because the Soviet Union has declared war against us."; he then held an Imperial conference during which he authorised minister Togo to notify the Allies that Japan would accept their terms on one condition, that the declaration "does not compromise any demand which prejudices the prerogatives of His Majesty as a Sovereign ruler."

On the 10th August, the Japanese government presented a letter of protest for the atomic bombings to the government of the USA, via the government of Switzerland; on the 12th August, the Emperor informed the imperial family of his decision to surrender; one of his uncles, Prince Asaka, then asked whether the war would be continued if the kokutai could not be preserved; Hirohito simply replied "of course."; As the Allied terms seemed to leave intact the principle of the preservation of the Throne, Hirohito recorded on the 14th August his capitulation announcement which was broadcast to the Japanese nation the next day despite a short rebellion by militarists opposed to the surrender.

In his declaration, Hirohito referred to the atomic bombings: "Moreover, the enemy now possesses a new and terrible weapon with the power to destroy many innocent lives and do incalculable damage. Should we continue to fight, not only would it result in an ultimate collapse and obliteration of the Japanese nation, but also it would lead to the total extinction of human civilization. Such being the case, how are We to save the millions of Our subjects, or to atone Ourselves before the hallowed spirits of Our Imperial Ancestors? This is the reason why We have ordered the acceptance of the provisions of the Joint Declaration of the Powers."

On the 15th August 1945, six days after the bombing of Nagasaki, Emperor Hirohito authorised the final decision to surrender and Japan announced its surrender to the Allies, signing the Instrument of Surrender on the 2nd September 1945, officially ending WWII.

In his "Rescript to the soldiers and sailors" delivered on the 17th August, he stressed the impact of the Soviet invasion and his decision to surrender, omitting any mention of the bombs; during the year after the bombing, approximately 40,000 USA troops occupied Hiroshima, while Nagasaki was occupied by 27,000 troops.

Within the first 2 to 4 months of the bombings, the acute effects killed 90,000 to 166,000 people in Hiroshima and 60,000 to 80,000 in Nagasaki, with roughly half of the deaths in each city occurring on the first day; the Hiroshima prefecture health department estimated that, of the people who died on the day of the explosion, 60% died from flash or flame burns, 30% from falling debris and 10% from other causes; during the following months, large numbers died from the effect of burns, radiation sickness and other injuries, compounded by illness.

In a U.S. estimate of the total immediate and short term cause of death, (15 to 20)% died from radiation sickness, (20 to 30)% from burns and (50 to 60)% from other injuries, compounded by illness; in both cities, most of the dead were civilians, although Hiroshima had a sizeable garrison.

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