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Atomic Bombing of Hiroshima and Nagasaki

Contributor: C. Peter Chen

ww2dbaseThis article covers the atomic bombing of Hiroshima and Nagasaki. For details on the conventional bombing of Japan, please see the article Bombing of Tokyo and Other Cities.

ww2dbaseOn 16 Jul 1945, while President of the United States Harry Truman was at Potsdam, Germany to meet with his Allied counterparts, long-waited results reached him: The Manhattan Project, the American effort at building the atomic bomb, successfully detonated the first bomb during a test at Los Alamos, New Mexico, United States. Truman, unwilling to risk the huge amount of lives that might be lost on both sides should the Allies invade the Japanese home islands, ordered the usage of the new technology. The scientists presented them with two such weapons, while the military sought uranium to produce a third.

ww2dbaseTarget Selection

ww2dbaseBetween 10 and 11 May 1945, Oppenheimer led a committee which came up with a list of cities most potentially suitable as targets of atomic attacks. The committee eventually arrived at the recommendation of four targets: Kyoto, Hiroshima, Yokohama, and Kokura.

ww2dbaseHiroshima was chosen as the first target due to its military and industrial values. As a military target, Hiroshima was a major army base that housed the headquarters of the Japanese 5th Division and the 2nd Army Headquarters. It was also an important port in southern Japan and a communications center. The mountains surrounding Hiroshima also contributed to Hiroshima being among one of the top choices among the short list of potential targets, for that the mountains might contain the destructive forces of an atomic blast in the target area, increasing the level of destruction.

ww2dbaseUS Secretary of War Henry Stimson voiced successfully against the selection of Kyoto as a target, arguing that the city held cultural importance to the world; he also had a personal attachment to the city as he and his wife traveled to Kyoto on their honeymoon many years prior.

ww2dbasePrior to the bombing, the United States Army conducted many missions over Japanese cities that were composed of very few B-29 bombers. The purpose of such flights were to wear down the alertness of Japanese anti-aircraft defense crew, whether gunners or fighter pilots, so that when the atomic bomb attacks arrived, perhaps some of the Japanese would let their guards down.

ww2dbaseHiroshima

6 Aug 1945

ww2dbaseThe B-29 Superfortress bomber Enola Gay of USAAF 393rd Bombardment Squadron, commanded by Colonel Paul Tibbets of the 509 Composite Bombardment Group, XX Air Force, lifted off from North Field of Tinian of the Mariana Islands on 6 Jun 1945 with their cargo code named "Little Boy". The crew was instructed that Hiroshima was to be their primary target; if Hiroshima could not be reached for any reason, including foul weather, Kokura or Nagasaki was to be chosen as alternate targets. They were accompanied by two other B-29 bombers which carried instrumentation and photography equipment. US Navy Captain William Parsons armed the bomb en route, and 30 minutes prior to reaching Hiroshima 2nd Lieutenant Morris Jeppson removed the bomb's safety devices. Enola Gay was accompanied by two other B-29 bombers: Great Artiste, with scientific instruments, was piloted by Major Charles Sweeney; Necessary Evil, with photography equipment, was piloted by Captain George Marquardt.

ww2dbaseAbout 60 minutes before the American bombers reached Hiroshima, they were detected by Japanese radar. Air raid warnings were sounded in several cities, including Hiroshima, but when it was determined that there were only three bombers, thus it was likely to be only a reconnaissance mission, some of the cities lifted the alarm. The Japanese military determined that aviation fuel was so precious that interceptors would not be launched just for three bombers. This might be caused from the regular visits that the US Army had been sending for the very purpose of making the Japanese lower their guards.

ww2dbaseWhen the bombers reached Hiroshima, they found the weather conditions to be ideal. At 0815 hours local time, from an altitude of 9,855 meters, "Little Boy" was released by bombardier Thomas Ferebee. 57 seconds later, at the predetermined altitude of 600 meters, the bomb detonated directly over Shima Surgical Clinic; the original aiming point was the Aioi Bridge, but wind blew it off course. The resulting blast was measured at 13 kilotons of TNT, reducing an area of one mile in radius to total ruin. Fires were started across an area 11.4 square-kilometers in size. Tibbets recalled:

A bright light filled the plane. The first shockwave hit us. We were eleven and a half miles slant range from the atomic explosion but the whole airplane cracked and crinkled from the blast.... We turned back to look at Hiroshima. The city was hidden by that awful cloud... mushrooming, terrible and incredibly tall.

ww2dbaseYoko Ota, a Japanese writer at Hiroshima at the time, could not comprehend what had happened to the city.

I could not understand why our surroundings had changed so greatly in one instant. I thought it might have been something which had nothing to do with the war, the collapse of the earth which it was said would take place at the end of the world.

ww2dbaseAbout 70,000 to 80,000 people were killed immediately, many of whom probably had no idea what had happened. The 560 grams of Uranium 235 took about 10 nanoseconds of fission before a flash of light burst out of the bomb casing, releasing the first wave of gamma rays that traveled nearly at the speed of light. In 1/10,000 of a second, a second burst of gamma rays was released. In 3 milliseconds, a plasma fireball began to form. In 91 milliseconds, the bottom of the plasma fireball began to reach the top of the tallest buildings beneath the detonation. Soon after, a shock wave which traveled at twice the speed of sound came. The human nervous system required 1/30 of a second to register, and 1/10 of a second to flinch, thus for those who were close to the detonation, the blood in the victims' brains were likely evaporating before they could feel anything.

ww2dbaseThey were the lucky ones. Many of the about 70,000 who were injured by the bomb suffered much worse fate.

ww2dbaseMany who survived the initial flash became severely burned, even though the flash only lasted for a fraction of a second. Many people who were burned so quickly and so severely that, as survivors told, they resembled living pieces of charcoal, wandering mindlessly unless they collapsed and died. Many people were miraculously saved by shock cocoons, thick concrete walls, or other opportune defense against the gamma rays, fireball, and shock wave, but many of them would fall victim of radiation poisoning, some dying violently while vomiting out their insides while others simply slipped away. While doctors and other medical professionals could do little for the radiation poisoning that they knew nothing about, they could do little even with the more traditional injuries. Most of the city's hospitals were located in the area of Hiroshima that was destroyed, thus over 90% of medical professionals were killed at the moment of detonation. On top of that, medical equipment, medicine, and most other things that they needed to treat their patients were destroyed. To make matters worse, radiation was at dangerous levels even days after the explosion, thus some of those who escaped harm without even a single bruise would suddenly lose all their hair and suffer unstoppable nosebleeds seemingly out of nowhere. By the end of 1945, Hiroshima's atomic bomb victims would increase to somewhere between 90,000 and 150,000.

ww2dbaseA significant portion of those who were killed at Hiroshima were Korean workers. It was estimated that 10,000 to 20,000 Koreans made up of the total 70,000 to 80,000 who died in the initial few days of the bombing.

ww2dbaseAs Hiroshima suddenly turned into a manifestation of hell on Earth, with an estimated 69% of the city destroyed, it was difficult for anyone to believe that "Little Boy" actually misfired: only 1.38% of its Uranium fissiled.

ww2dbaseIt was unknown who first reported the terrible news to Tokyo, but it certainly did not come from Hiroshima. One of the first military reports came from the naval base at Kure, fifteen miles south of Hiroshima. From the civilian side, the Tokyo facilities of the Japanese Broadcasting Corporation noticed that the Hiroshima station had gone off the air, and attempts to reach the station by telephone had failed. Since no large formations of bombers were detected, Japanese leadership generally thought that, despite rumors of a horrible explosion, whatever had happened probably was not as serious as the rumors suggested. An Army pilot was dispatched to fly a staff officer over Hiroshima to provide an accurate report. While still 160 kilometers from Hiroshima, they observed thick black smoke rising from the city. As they got closer, the level of destruction could no longer be denied. "Practically all living things, human and animal, were literally seared to death", reported a Japanese radio station hours later.

ww2dbaseWith all communications capability and infrastructure destroyed in the Hiroshima area, reports with exact details flowed in extremely slowly delaying any kind of decision process. The Japanese government, completely in a state of shock, did not communicate with the Allies. Truman initially ordered a halt of bombings on Japan, but as he received no words from Tokyo, he took the lack of response as a sign of Japanese arrogance and a sign of the refusal to surrender. "If they do not now accept our terms, they may expect a rain of ruin from the air the likes of which has never been seen on this earth", he said. He later gave the go-ahead to drop the second atomic weapon on Japan.

ww2dbaseNagasaki

9 Aug 1945

ww2dbaseThe second bombing was originally planned to be against the city of Kokura, which housed a major army arsenal, on 11 Aug. The schedule was moved up by two days to 9 Aug, however, due to predicted bad weather moving in on 10 Aug. The atomic bomb "Fat Man" was loaded onto B-29 Superfortress bomber Bockscar, commanded by Major Charles Sweeney of USAAF 393rd Squadron, who had piloted the bomber Great Artiste during the Hiroshima atomic bombing. Similar to the Hiroshima attack, two other B-29 bombers accompanied Bockscar; the Great Artiste, piloted by Captain Frederick Bock (who usually flew Bockscar, named after himself), with scientific instrumentation and Big Stink, piloted by Lieutenant Colonel James Hopkins, Jr., with photography equipment. Unlike the Hiroshima attack, "Fat Man" was already armed when the bomber took off due to the complexity of the Plutonium bomb. This concerned Sweeney, as this meant that a big jolt, not overly rare during takeoffs, might detonate the bomb if the electrical safety plugs failed; as history would show, an accidental detonation did not happen. As Bockscar began its approach toward Japan, fuel would be his only concern; the bomber had a problem with the transfer pump with his reserve fuel tank, and the mission was deemed too important to be delayed simply for a malfunctioning pump.

ww2dbaseWhen Bockscar and Great Artiste reached the rendezvous point, however, Big Stink was nowhere to be found. Unable to locate him after 40 minutes, Sweeney decided to proceed with the mission without Big Stink.

ww2dbaseSweeney had hoped that, despite better defended by the Japanese, the skies over Kokura would be clear enough for them to conduct the bomb run. He knew the Kokura was a much greater military target when compared to the secondary target, Nagasaki. To his disappointment, Kokura was 70% cloud covered. He was ordered that the bombardier must be able to visually identify the target point before releasing the bomb, thus he made three runs over Kokura, expending the precious fuel that he had little of. All three runs failed to give them the chance to properly identify their target, and Sweeney made the decision to go for the secondary target, Nagasaki. Had he had enough fuel, he would have flown in a northwestern direction, then circle back for an eastward approach for Nagasaki; given his fuel situation, Sweeney had his navigator plot a straight line for his target. A quick calculation revealed that, even if they only make one run at Nagasaki and head straight to Okinawa, rather than Iwo Jima as originally planned, they already had too little fuel to make the trip.

ww2dbaseThe city of Nagasaki was one of the most important sea ports in southern Japan. Although it was not among the list of potential targets selected by Oppenheimer's committee, it was added later due to its significance as a major war production center for warships, munitions, and other equipment. This was the very reason why Sweeney hoped that Kokura would have clear weather for the attack, thus avoiding an attack on Nagasaki which housed a greater civilian population.

ww2dbaseAt 0750 hours in the morning of 9 Aug, the presence of American bombers in the general area in southern Japan caused the city of Nagasaki to sound the air raid alarms, but the "all clear" signal was given at 0830. The two attacking bombers were visually detected at Nagasaki at 1053, but like at Hiroshima many radar station commanding officers thought this small flight must be on a reconnaissance mission; a few radar station operators who had learned about Hiroshima, however, knew what was coming, and braced for impact. As Bockscar approached, US Navy Commander Frederick Ashworth, the weaponeer, approved Sweeney's request to drop the bomb by radar, rather than by establishing visual contact with the aiming point, should weather once again interfere.

ww2dbaseAt about 1100 hours, bombardier Captain Kermit Beahan aboard Bockscar, previously unable to find his original aiming point near the center of Nagasaki, found a break in the clouds directly over another aiming point. This aiming point was over the Urakami Valley that housed the namesake district in the Nagasaki suburbs, which hosted industrial complexes devoted to war production. Beahan signaled that he was ready to proceed with the attack.

ww2dbaseAt 1100 hours, the Great Artiste, the scientific aircraft, dropped instruments attached to three parachutes. Also inside this package was an unsigned letter to Professor Ryokichi Sagane, a leading nuclear physicist of Japan who had befriended American nuclear physicists prior to the war, urging him to advise Japanese leadership to surrender to avoid further atomic attacks.

ww2dbaseAt 1101 hours, Beahan released the bomb over Urakami. 43 seconds later, the "Fat Man" bomb containing about 6.4 kilograms of Plutonium 239 detonated at the altitude of 469 meters over the halfway point between the Mitsubishi Steel and Arms Works in the south and the Mitsubishi-Urakami Ordnance Works (a factory producing torpedoes) in the north. Ground Zero was about 3 kilometers northwest of the original aiming point near the center of Nagasaki. The resulting blast was much greater than the "Little Boy" blast that devastated Hiroshima three days earlier. Somewhere between 40,000 to 75,000 people were immediately killed by the explosion equivalent to the detonation of 21 kilotons of TNT, and everything within 1 kilometer from Ground Zero were reduced to total ruin. Fires were started as far as 3.2 kilometers from Ground Zero. The heat generated by the bomb was estimated at 3,900 degrees Celcius, and the blast created winds up to 1,005 kilometers per hour in speed. Because the detonation had taken place in a valley, the center of Nagasaki was shielded by the mountains and hills that surrounded Urakami, thus large parts of Nagasaki proper were relatively unharmed by the initial blast. By the end of 1945, death tolls directly related to "Fat Man" reached 80,000.

ww2dbaseAbout 2,000 of the deaths at Nagasaki were Korean workers.

ww2dbaseAs Bockscar flew toward Okinawa after the bombing, Sweeney did everything he could to conserve fuel. He lowered the speed of his propellers, while he lowered his altitude periodically to gravity to increase his speed rather than using his fuel. When he had Okinawa in sight, one of his engines gave out. After he was not able to get any control tower's attention, he fired off every single emergency flare he had in Bockscar, and his apparently strange act finally got someone attention, and made a safe landing quite literally on the last drops of fuel. As the B-29 aircraft was surrounded by fire trucks and ambulances (his display of flares signaled all kinds of emergencies), a high-level order came from Tinian Island, requiring the crews at Okinawa to give whatever Bockscar required for a return trip to Tinian.

ww2dbaseGeorge Weller, one of the first reporters to reach Nagasaki after the attack, and certainty the first western journalist to do so, compiled a report that was censored and would not become published until Jun 2005. In it, he noted:

Look at the pushed-in façade of the American consulate, three miles from the blast's center, or the face of the Catholic cathedral, one mile in the other direction, torn down like gingerbread, and you can tell that the liberated atom spares nothing in its way.

ww2dbaseEpilogue

ww2dbaseOn the very same day of the Nagasaki bombing, the Soviet Union tore up her non-aggression pact with Japan and invaded the Japanese-held northeastern China. The triple shock of Hiroshima, Nagasaki, and the new front against Russia finally pushed Japan definitively toward settling for peace. Should Japan choose to continue the war, however, the United States expected to complete a third atomic bomb by late Aug or early Sep, with three more in Sep, and plans to use them were certainly being considered.

ww2dbaseRecall that during the Nagasaki bombing, American scientists inserted an unsigned letter to Professor Ryokichi Sagane in the instruments that were dropped just prior to the bomb to record scientific data. The letter urged Sagane to advise Japanese leadership to surrender to avoid further atomic attacks. This letter actually did not get delivered to him until a month later. In 1949, American nuclear physicist Luis Alvarez who had been a friend of Sagane's from before the war revealed himself to be one of the authors of this letter; he met with Sagane and signed the letter.

ww2dbaseSources: Mainichi Daily News, the Last Train from Hiroshima, the Pacific Campaign, Wikipedia.

Last Major Update: Mar 2010

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