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160-627: On the day Hiroshima was destroyed by an atomic bomb , a single Ki-51 was responsible for the last Japanese sinking of a US warship, sinking USS  Bullhead  (SS-332) with all hands. The only complete survivor of Ki-51 is part of the collection of the Dirgantara Mandala Museum in Indonesia. The aircraft was found abandoned at the Babo Airfield in West Papua province . The aircraft

320-476: A cluster bomb or "cookie-cutter" configuration. It has been reported that during the height of the Cold War in the 1970s Moscow was targeted by up to 60 warheads. The reason that the cluster bomb concept is preferable in the targeting of cities is twofold: the first is that large singular warheads are much easier to neutralize as both tracking and successful interception by anti-ballistic missile systems than it

480-399: A 1 kt bomb is 0.22  km; for 100 kt, 1  km; and for 10 Mt, 4.7  km. Two distinct, simultaneous phenomena are associated with the blast wave in the air: Most of the material damage caused by a nuclear air burst is caused by a combination of the high static overpressures and the blast winds. The long compression of the blast wave weakens structures, which are then torn apart by

640-549: A Fat Man was dropped on Nagasaki. Over the next two to four months, the effects of the atomic bombings killed 90,000 to 166,000 people in Hiroshima and 60,000 to 80,000 people in Nagasaki; roughly half occurred on the first day. For months afterward, many people continued to die from the effects of burns, radiation sickness , and other injuries, compounded by illness and malnutrition. Despite Hiroshima's sizable military garrison, most of

800-482: A brighter color, such as asphalt. If such a weather phenomenon as fog or haze is present at the point of the nuclear explosion, it scatters the flash , with radiant energy then reaching burn-sensitive substances from all directions. Under these conditions, opaque objects are therefore less effective than they would otherwise be without scattering, as they demonstrate maximum shadowing effect in an environment of perfect visibility and therefore zero scatterings. Similar to

960-415: A certain reflection angle, the reflected wave and the direct wave merge and form a reinforced horizontal wave, known as the '" Mach stem " and is a form of constructive interference . This phenomenon is responsible for the bumps or 'knees' in the above overpressure range graph. For each goal overpressure, there is a certain optimum burst height at which the blast range is maximized over ground targets. In

1120-432: A foggy or overcast day, although there are few if any, shadows produced by the sun on such a day, the solar energy that reaches the ground from the sun's infrared rays is nevertheless considerably diminished, due to it being absorbed by the water of the clouds and the energy also being scattered back into space. Analogously, so too is the intensity at a range of burning flash energy attenuated, in units of J /cm , along with

1280-628: A greater loss of life; according to critics, the bombings were unnecessary for the war's end and were a war crime , raising moral and ethical implications. In 1945, the Pacific War between the Empire of Japan and the Allies entered its fourth year. Most Japanese military units fought fiercely, ensuring that the Allied victory would come at an enormous cost. The 1.25 million battle casualties incurred in total by

1440-407: A large amount of radioactive material is released into the environment. This form of radioactive contamination is known as nuclear fallout and poses the primary risk of exposure to ionizing radiation for a large nuclear weapon. Details of nuclear weapon design also affect neutron emission: the gun-type assembly Little Boy leaked far more neutrons than the implosion-type 21 kt Fat Man because

1600-401: A large area of Nagasaki , no true firestorm occurred in the city even though a higher yielding weapon was used. Many factors explain this seeming contradiction, including a different time of bombing than Hiroshima, terrain, and crucially, a lower fuel loading/fuel density than that of Hiroshima. Nagasaki probably did not furnish sufficient fuel for the development of a firestorm as compared to

1760-490: A large fraction of the city may be destroyed. The Emperor's palace in Tokyo has a greater fame than any other target but is of least strategic value." Edwin O. Reischauer , a Japan 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: ... the only person deserving credit for saving Kyoto from destruction

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1920-423: A large war industry, manufacturing parts for planes and boats, for bombs, rifles, and handguns. The center of the city contained several reinforced concrete buildings. Outside the center, the area was congested by a dense collection of small timber workshops set among Japanese houses. A few larger industrial plants lay near the outskirts of the city. The houses were constructed of timber with tile roofs, and many of

2080-785: A leaflet listing 11 or 12 cities targeted for firebombing; a total of 33 cities listed. With the text of this leaflet reading in Japanese "...   we cannot promise that only these cities will be among those attacked   ..." Hiroshima was not listed. In 1943, the United States and the United Kingdom signed the Quebec Agreement , which stipulated that nuclear weapons would not be used against another country without mutual consent. Stimson therefore had to obtain British permission. A meeting of

2240-537: A leaflet. Leaflet texts were prepared by recent Japanese prisoners of war because they were thought to be the best choice "to appeal to their compatriots". In preparation for dropping an atomic bomb on Hiroshima, the Oppenheimer-led Scientific Panel of the Interim Committee decided against a demonstration bomb and against a special leaflet warning. Those decisions were implemented because of

2400-455: A localized earthquake event is more probable. The first and fastest wave, equivalent to a normal earthquake's P wave , can inform the location of the test; the S wave and the Rayleigh wave follow. These can all be measured in most circumstances by seismic stations across the globe, and comparisons with actual earthquakes can be used to help determine estimated yield via differential analysis, by

2560-525: A meeting with the President and commanders on 18 June 1945, General George C. Marshall stated that "there was reason to believe" casualties for the first 30 days would not exceed the price paid for Luzon . Additionally, with the Japanese position rendered "hopeless" by an invasion of their mainland, Marshall speculated that Soviet entry into the war might be "the decisive action" needed to finally "[leverage] them into capitulation." Marshall began contemplating

2720-493: A moderate rain storm during an Operation Castle nuclear explosion were found to dampen, or reduce, peak pressure levels by approximately 15% at all ranges. Much of the destruction caused by a nuclear explosion is from blast effects. Most buildings, except reinforced or blast-resistant structures, will suffer moderate damage when subjected to overpressures of only 35.5 kilopascals (kPa) (5.15 pounds-force per square inch or 0.35 atm). Data obtained from Japanese surveys following

2880-463: A nuclear detonation . Eventually the shock wave dissipates to the point where the light becomes visible again giving rise to the characteristic double flash caused by the shock wave–fireball interaction. It is this unique feature of nuclear explosions that is exploited when verifying that an atmospheric nuclear explosion has occurred and not simply a large conventional explosion, with radiometer instruments known as Bhangmeters capable of determining

3040-406: A nuclear weapon is surrounded only by air, lethal blast and thermal effects proportionally scale much more rapidly than lethal radiation effects as explosive yield increases. This bubble is faster than the speed of sound . The physical damage mechanisms of a nuclear weapon (blast and thermal radiation) are identical to those of conventional explosives, but the energy produced by a nuclear explosion

3200-549: A peak of over 381,000 earlier in the war but prior to the atomic bombing, the population had steadily decreased because of a systematic evacuation ordered by the Japanese government . At the time of the attack, the population was approximately 340,000–350,000. Residents wondered why Hiroshima had been spared destruction by firebombing. Some speculated that the city was to be saved for U.S. occupation headquarters, others thought perhaps their relatives in Hawaii and California had petitioned

3360-537: A point of comparison in the chart below, the most likely nuclear weapons to be used against countervalue city targets in a global nuclear war are in the sub-megaton range. Weapons of yields from 100 to 475 kilotons have become the most numerous in the US and Russian nuclear arsenals; for example, the warheads equipping the Russian Bulava submarine-launched ballistic missile ( SLBM ) have a yield of 150 kilotons. US examples are

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3520-573: A press conference that the Potsdam Declaration was no more than a rehash ( yakinaoshi ) of the Cairo Declaration , that the government intended to ignore it ( mokusatsu , "kill by silence"), and that Japan would fight to the end. 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

3680-498: A request from Winston Churchill that Britain be represented when the atomic bomb was dropped. William Penney and Group Captain Leonard Cheshire were sent to Tinian, but LeMay would not let them accompany the mission. The Little Boy bomb, except for the uranium payload, was ready at the beginning of May 1945. There were two uranium-235 components, a hollow cylindrical projectile and a cylindrical target insert. The projectile

3840-399: A result, the initial radiation becomes less of a hazard with increasing yield. With larger weapons, above 50 kt (200 TJ), blast and thermal effects are so much greater in importance that prompt radiation effects can be ignored. The neutron radiation serves to transmute the surrounding matter, often rendering it radioactive . When added to the dust of radioactive material released by the bomb,

4000-540: A series of landings by the U.S. Sixth Army intended to capture the southern third of the southernmost main Japanese island, Kyūshū . This was to be followed in March 1946 by Operation Coronet , the capture of the Kantō Plain , near Tokyo on the main Japanese island of Honshū by the U.S. First , Eighth and Tenth Armies, as well as a Commonwealth Corps made up of Australian, British and Canadian divisions. The target date

4160-461: A series of raids on strategic targets in Japan. This effort failed to achieve the strategic objectives that its planners had intended, largely because of logistical problems, the bomber's mechanical difficulties, the vulnerability of Chinese staging bases, and the extreme range required to reach key Japanese cities. Brigadier General Haywood S. Hansell determined that Guam , Tinian , and Saipan in

4320-676: A study by the Joint War Plans Committee, drawing on the experience of the Battle of Leyte , estimated that Downfall would result in 132,500 to 220,000 U.S. casualties, with U.S. dead and missing in the range from 27,500 to 50,000. Secretary of War Henry L. Stimson commissioned his own study by Quincy Wright and William Shockley , who estimated the invading Allies would suffer between 1.7 and 4 million casualties, of whom between 400,000 and 800,000 would be dead, while Japanese fatalities would have been around 5 to 10 million. In

4480-482: A total dose of one gray , "lethal" to ten grays. This is only a rough estimate since biological conditions are neglected here. Further complicating matters, under global nuclear war scenarios with conditions similar to that during the Cold War , major strategically important cities like Moscow and Washington are likely to be hit numerous times from sub-megaton multiple independently targetable re-entry vehicles , in

4640-420: A typical air burst, where the blast range is maximized to produce the greatest range of severe damage, i.e. the greatest range that ~10 psi (69 kPa) of pressure is extended over, is a GR/ground range of 0.4 km for 1 kiloton (kt) of TNT yield; 1.9 km for 100 kt; and 8.6 km for 10 megatons (Mt) of TNT. The optimum height of burst to maximize this desired severe ground range destruction for

4800-622: Is Henry L. Stimson, the Secretary of War at the time, who had known and admired Kyoto ever since his honeymoon there several decades earlier. Extant sources show that while Stimson was personally familiar with Kyoto, this was the result of a visit decades after his marriage, not because he honeymooned there. On 30 May, Stimson asked Groves to remove Kyoto from the target list due to its historical, religious and cultural significance, but Groves pointed to its military and industrial significance. Stimson then approached President Harry S. Truman about

4960-406: Is at the same temperature as the fuel powering the explosion). This causes vaporization of the surrounding material, resulting in its rapid expansion. Kinetic energy created by this expansion contributes to the formation of a shock wave which expands spherically from the center. Intense thermal radiation at the hypocenter forms a nuclear fireball which, if the explosion is low enough in altitude,

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5120-403: Is caused by the initial brilliant flash of light produced by the nuclear detonation. More light energy is received on the retina than can be tolerated but less than is required for irreversible injury. The retina is particularly susceptible to visible and short wavelength infrared light since this part of the electromagnetic spectrum is focused by the lens on the retina. The result is bleaching of

5280-430: Is close enough to the nuclear fireball to be drawn into it, and is thus heated to the necessary temperatures to do so; this is known as trinitite . At the explosion of nuclear bombs lightning discharges sometimes occur. Smoke trails are often seen in photographs of nuclear explosions. These are not from the explosion; they are left by sounding rockets launched just prior to detonation. These trails allow observation of

5440-441: Is common for long-range early warning radars . The effect is less for higher frequencies in the microwave region, as well as lasting a shorter time – the effect falls off both in strength and the affected frequencies as the fireball cools and the electrons begin to re-form onto free nuclei. A second blackout effect is caused by the emission of beta particles from the fission products . These can travel long distances, following

5600-447: Is entirely different from the gamma-ray induced pulse produced by Compton electrons. The heat of the explosion causes air in the vicinity to become ionized, creating the fireball. The free electrons in the fireball affect radio waves, especially at lower frequencies. This causes a large area of the sky to become opaque to radar, especially those operating in the VHF and UHF frequencies, which

5760-419: Is from kinetic energy. For an explosion in the atmosphere, the fireball quickly expands to maximum size and then begins to cool as it rises like a balloon through buoyancy in the surrounding air. As it does so, it takes on the flow pattern of a vortex ring with incandescent material in the vortex core as seen in certain photographs. This effect is known as a mushroom cloud . Sand will fuse into glass if it

5920-486: Is generally to the contrary to what other less technical sources state. The "oily" black soot particles, are a characteristic of incomplete combustion in the city firestorm. The element einsteinium was discovered when analyzing nuclear fallout. A side-effect of the Pascal-B nuclear test during Operation Plumbbob may have resulted in the first man-made object launched into space. The so-called "thunder well" effect from

6080-413: Is highly likely and radiation poisoning is almost certain if one is caught in the open with no terrain or building masking effects within a radius of 0–3 kilometres (0.0–1.9 mi) from a 1 megaton airburst, and the 50% chance of death from the blast extends out to ~8 kilometres (5.0 mi) from the same 1 megaton atmospheric explosion. An example that highlights the variability in the real world and

6240-477: Is not the case with thermionic tubes (or valves) which are relatively immune to EMP. A Faraday cage does not offer protection from the effects of EMP unless the mesh is designed to have holes no bigger than the smallest wavelength emitted from a nuclear explosion. Large nuclear weapons detonated at high altitudes also cause geomagnetically induced current in very long electrical conductors. The mechanism by which these geomagnetically induced currents are generated

6400-417: Is often associated with a mushroom cloud . In a high-altitude burst where the density of the atmosphere is low, more energy is released as ionizing gamma radiation and X-rays than as an atmosphere-displacing shockwave. The high temperatures and radiation cause gas to move outward radially in a thin, dense shell called "the hydrodynamic front". The front acts like a piston that pushes against and compresses

6560-410: Is responsible for warming the atmospheric nitrogen close to the bomb and causing the creation of atmospheric NOx smog components. This, as part of the mushroom cloud , is shot into the stratosphere where it is responsible for dissociating ozone there , in the same way combustion NOx compounds do. The amount created depends on the yield of the explosion and the blast's environment. Studies done on

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6720-416: 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 Target Committee stated that "It was agreed that psychological factors in the target selection were of great importance. Two aspects of this are (1) obtaining

6880-404: Is that this tactic along with limiting the risk of failure reduces individual bomb yields, and therefore reduces the possibility of any serious collateral damage to non-targeted nearby civilian areas, including that of neighboring countries. This concept was pioneered by Philip J. Dolan and others. Gamma rays from the nuclear processes preceding the true explosion may be partially responsible for

7040-404: Is usually millions of times more powerful per unit mass, and temperatures may briefly reach the tens of millions of degrees. Energy from a nuclear explosion is initially released in several forms of penetrating radiation. When there is surrounding material such as air, rock, or water, this radiation interacts with and rapidly heats the material to an equilibrium temperature (i.e. so that the matter

7200-464: Is when several smaller incoming warheads are approaching. This strength in numbers advantage to lower yield warheads is further compounded by such warheads tending to move at higher incoming speeds, due to their smaller, more slender physics package size, assuming both nuclear weapon designs are the same (a design exception being the advanced W88 ). The second reason for this cluster bomb, or 'layering' (using repeated hits by accurate low yield weapons)

7360-653: The Boeing B-29 Superfortress , and deployed to Tinian in the Mariana Islands . The Allies called for the unconditional surrender of the Imperial Japanese armed forces in the Potsdam Declaration on 26 July 1945, the alternative being "prompt and utter destruction". The Japanese government ignored the ultimatum. The consent of the United Kingdom was obtained for the bombing, as was required by

7520-601: The Combined Policy Committee , which included one Canadian representative, was held at the Pentagon on 4 July 1945. Field Marshal Sir Henry Maitland Wilson announced that the British government concurred with the use of nuclear weapons against Japan, which would be officially recorded as a decision of the Combined Policy Committee. As the release of information to third parties was also controlled by

7680-534: The Einstein–Szilard letter to Roosevelt in 1939. This prompted preliminary research in the United States in late 1939. Progress was slow until the arrival of the British MAUD Committee report in late 1941, which indicated that only 5 to 10 kilograms of isotopically -pure uranium-235 were needed for a bomb instead of tons of natural uranium and a neutron moderator like heavy water . Consequently,

7840-544: The Interim Committee was created by Stimson at the urging of leaders of the Manhattan Project and with the approval of Truman to advise on matters pertaining to nuclear technology . They agreed that the atomic bomb was to be used (1) against Japan at the earliest opportunity, (2) without special warning, and (3) on a "dual target" of military installation surrounded by other buildings susceptible to damage. During

8000-512: 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 October 1944. The XXI Bomber Command began missions against Japan on 18 November 1944. The early attempts to bomb Japan from

8160-467: The Quebec Agreement , and orders were issued on 25 July by General Thomas Handy , the acting chief of staff of the United States Army , for atomic bombs to be used against Hiroshima, Kokura , Niigata , and Nagasaki. These targets were chosen because they were large urban areas that also held militarily significant facilities. On 6v August, a Little Boy was dropped on Hiroshima. Three days later,

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8320-571: The W76 and W88 warheads, with the lower yield W76 being over twice as numerous as the W88 in the US nuclear arsenal. For the direct radiation effects the slant range instead of the ground range is shown here because some effects are not given even at ground zero for some burst heights. If the effect occurs at ground zero the ground range can be derived from slant range and burst altitude ( Pythagorean theorem ). "Acute radiation syndrome" corresponds here to

8480-467: The abdominal cavity , which contain air, are particularly injured. The damage causes severe hemorrhaging or air embolisms , either of which can be rapidly fatal. The overpressure estimated to damage lungs is about 70 kPa. Some eardrums would probably rupture around 22 kPa (0.2 atm) and half would rupture between 90 and 130 kPa (0.9 to 1.2 atm). Nuclear weapons emit large amounts of thermal radiation as visible, infrared, and ultraviolet light, to which

8640-416: The atomic bombings of Hiroshima and Nagasaki found that 8 psi (55 kPa) was sufficient to destroy all wooden and brick residential structures. This can reasonably be defined as the pressure capable of producing severe damage. The blast wind at sea level may exceed 1,000 km/h, or ~300 m/s, approaching the speed of sound in air. The range for blast effects increases with the explosive yield of

8800-419: The electromagnetic spectrum , with the surroundings. The environment of the explosion (e.g. submarine, ground burst , air burst , or exo-atmospheric) determines how much energy is distributed to the blast and how much to radiation. In general, surrounding a bomb with denser media, such as water, absorbs more energy and creates more powerful shock waves while at the same time limiting the area of its effect. When

8960-481: The instrument of surrender on 2 September, effectively ending the war . In the final year of World War II , the Allies prepared for a costly invasion of the Japanese mainland . This undertaking was preceded by a conventional bombing and firebombing campaign that devastated 64 Japanese cities, including an operation on Tokyo . The war in the European theatre concluded when Germany surrendered on 8 May 1945, and

9120-428: The ionosphere . Electronics can be shielded by wrapping them completely in conductive material such as metal foil; the effectiveness of the shielding may be less than perfect. Proper shielding is a complex subject due to the large number of variables involved. Semiconductors , especially integrated circuits , are extremely susceptible to the effects of EMP due to the close proximity of their p–n junctions , but this

9280-399: The 393d Bombardment Squadron plus one from the 216th Army Air Force Base Unit, and transported to North Field, arriving on 2 August. At the time of its bombing, Hiroshima was a city of industrial and military significance. A number of military units were located nearby, the most important of which was the headquarters of Field Marshal Shunroku Hata 's Second General Army , which commanded

9440-422: The 3rd Anti-Aircraft Division, including units from the 121st and 122nd Anti-Aircraft Regiments and the 22nd and 45th Separate Anti-Aircraft Battalions. In total, an estimated 40,000 Japanese military personnel were stationed in the city. Hiroshima was a supply and logistics base for the Japanese military. The city was a communications center, a key port for shipping, and an assembly area for troops. It supported

9600-475: The 509th Composite Group about the possibility of a B-29 crashing on takeoff, Birch had modified the Little Boy design to incorporate a removable breech plug that would permit the bomb to be armed in flight. The first plutonium core , along with its polonium - beryllium urchin initiator , was transported in the custody of Project Alberta courier Raemer Schreiber in a magnesium field carrying case designed for

9760-523: The 509th Composite Group moved by rail on 26 April 1945, to its port of embarkation at Seattle , Washington. On 6 May the support elements sailed on the SS Cape Victory for the Marianas, while group materiel was shipped on the SS Emile Berliner . The Cape Victory made brief port calls at Honolulu and Eniwetok but the passengers were not permitted to leave the dock area. An advance party of

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9920-523: The 509th had attached to it on Tinian 51 civilian and military personnel from Project Alberta , known as the 1st Technical Detachment. The 509th Composite Group's 393d Bombardment Squadron was equipped with 15 Silverplate B-29s. These aircraft were specially adapted to carry nuclear weapons, and were equipped with fuel-injected engines, Curtiss Electric reversible-pitch propellers , pneumatic actuators for rapid opening and closing of bomb bay doors and other improvements. The ground support echelon of

10080-501: The Allies advanced towards Japan, conditions became steadily worse for the Japanese people. Japan's merchant fleet declined from 5,250,000 gross register tons in 1941 to 1,560,000 tons in March 1945, and 557,000 tons in August 1945. The lack of raw materials forced the Japanese war economy into a steep decline after the middle of 1944. The civilian economy, which had slowly deteriorated throughout

10240-484: The Allies turned their full attention to the Pacific War . By July 1945, the Allies' Manhattan Project had produced two types of atomic bombs: " Little Boy ", an enriched uranium gun-type fission weapon , and " Fat Man ", a plutonium implosion-type nuclear weapon . The 509th Composite Group of the United States Army Air Forces was trained and equipped with the specialized Silverplate version of

10400-639: The Earth's magnetic field lines. When they reach the upper atmosphere they cause ionization similar to the fireball but over a wider area. Calculations demonstrate that one megaton of fission, typical of a two-megaton H-bomb, will create enough beta radiation to blackout an area 400 kilometres (250 miles) across for five minutes. Careful selection of the burst altitudes and locations can produce an extremely effective radar-blanking effect. The physical effects giving rise to blackouts also cause EMP, which can also cause power blackouts. The two effects are otherwise unrelated, and

10560-528: The Earth's magnetic field to produce a coherent nuclear electromagnetic pulse (NEMP) which lasts about one millisecond. Secondary effects may last for more than a second. The pulse is powerful enough to cause moderately long metal objects (such as cables) to act as antennas and generate high voltages due to interactions with the electromagnetic pulse. These voltages can destroy unshielded electronics. There are no known biological effects of EMP. The ionized air also disrupts radio traffic that would normally bounce off

10720-462: The Manhattan Project took place at dozens of sites across the United States, and even some outside of its borders. It would ultimately cost over US$ 2 billion (equivalent to about $ 27 billion in 2023) and employ over 125,000 people simultaneously at its peak. Groves appointed J. Robert Oppenheimer to organize and head the project's Los Alamos Laboratory in New Mexico , where bomb design work

10880-706: The Marianas proved just as ineffective as the China-based B-29s had been. Hansell continued the practice of conducting so-called high-altitude precision bombing , aimed at key industries and transportation networks, even after these tactics had not produced acceptable results. These efforts proved unsuccessful due to logistical difficulties with the remote location, technical problems with the new and advanced aircraft, unfavorable weather conditions, and enemy action. Hansell's successor, Major General Curtis LeMay , assumed command in January 1945 and initially continued to use

11040-561: The Pacific, the Allies returned to the Philippines , recaptured Burma , and invaded Borneo . Offensives were undertaken to reduce the Japanese forces remaining in Bougainville , New Guinea and the Philippines. In April 1945, American forces landed on Okinawa , where heavy fighting continued until June. Along the way, the ratio of Japanese to American casualties dropped from five to one in

11200-461: The Philippines to two to one on Okinawa. Although some Japanese soldiers were taken prisoner , most fought until they were killed or committed suicide . Nearly 99 percent of the 21,000 defenders of Iwo Jima were killed. Of the 117,000 Okinawan and Japanese troops defending Okinawa in April to June 1945, 94 percent were killed; 7,401 Japanese soldiers surrendered, an unprecedentedly large number. As

11360-555: The Quebec Agreement, discussion then turned to what scientific details would be revealed in the press announcement of the bombing. The meeting also considered what Truman could reveal to Joseph Stalin , the leader of the Soviet Union , at the upcoming Potsdam Conference , as this also required British concurrence. Orders for the attack were issued to General Carl Spaatz on 25 July under the signature of General Thomas T. Handy ,

11520-451: The U.S. government to avoid bombing Hiroshima. More realistic city officials had ordered buildings torn down to create long, straight firebreaks . These continued to be expanded and extended up to the morning of 6 August 1945. Effects of nuclear explosions The effects of a nuclear explosion on its immediate vicinity are typically much more destructive and multifaceted than those caused by conventional explosives . In most cases,

11680-632: The USAAF; and scientists John von Neumann , Robert R. Wilson and William Penney from the Manhattan Project. The Target Committee met in Washington on 27 April; at Los Alamos on 10 May, where it was able to talk to the scientists and technicians there; and finally in Washington on 28 May, where it was briefed by Tibbets and Commander Frederick Ashworth from Project Alberta, and the Manhattan Project's scientific advisor, Richard C. Tolman . The Target Committee nominated five targets: Kokura (now Kitakyushu ),

11840-489: The United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki , respectively. The bombings killed between 150,000 and 246,000 people, most of whom were civilians, and remain the only use of nuclear weapons in an armed conflict. Japan surrendered to the Allies on 15 August, six days after the bombing of Nagasaki and the Soviet Union's declaration of war against Japan and invasion of Japanese-occupied Manchuria . The Japanese government signed

12000-541: The United States in World War II included both military personnel killed in action and wounded in action . Nearly one million of the casualties occurred during the last year of the war, from June 1944 to June 1945. In December 1944, American battle casualties hit an all-time monthly high of 88,000 as a result of the German Ardennes Offensive . Worried by the losses sustained, President Roosevelt suggested

12160-593: The acting chief of staff, since Marshall was at the Potsdam Conference with Truman. It read in part: That day, Truman noted in his diary that: This weapon is to be used against Japan between now and August 10th. I have told the Sec. of War, 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

12320-467: The air echelon, consisting of 29 officers and 61 enlisted men, flew by C-54 to North Field on Tinian, between 15 and 22 May. There were also two representatives from Washington, D.C., Brigadier General Thomas Farrell , the deputy commander of the Manhattan Project, and Rear Admiral William R. Purnell of the Military Policy Committee, who were on hand to decide higher policy matters on

12480-452: The air raids to preserve fighter aircraft to counter the expected invasion. By mid-1945 the Japanese only occasionally scrambled aircraft to intercept individual B-29s conducting reconnaissance sorties over the country, to conserve supplies of fuel. In July 1945, the Japanese had 137,800,000 litres (1,156,000 US bbl) of avgas stockpiled for the invasion of Japan. About 72,000,000 litres (604,000 US bbl) had been consumed in

12640-479: The atmosphere is largely transparent. This is known as "flash". The chief hazards are burns and eye injuries. On clear days, these injuries can occur well beyond blast ranges, depending on weapon yield. Fires may also be started by the initial thermal radiation, but the following high winds due to the blast wave may put out almost all such fires, unless the yield is very high where the range of thermal effects vastly outranges blast effects, as observed from explosions in

12800-485: The atomic attack, and the Japanese could deny the atomic bomb was lethal, making the mission less likely to produce surrender. Allied prisoners of war might be moved to the demonstration site and be killed by the bomb. They also worried that the bomb might be a failure, as the Trinity test was that of a stationary device, not an air-dropped bomb. In addition, although more bombs were in production, only two would be available at

12960-537: The blast wave effects such as from upset stoves and furnaces. In Hiroshima on 6 August 1945, a tremendous firestorm developed within 20 minutes after detonation and destroyed many more buildings and homes, built out of predominantly 'flimsy' wooden materials. A firestorm has gale-force winds blowing in towards the center of the fire from all directions. It is not peculiar to nuclear explosions, having been observed frequently in large forest fires and following incendiary raids during World War II. Despite fires destroying

13120-399: The blast winds. The compression, vacuum and drag phases together may last several seconds or longer, and exert forces many times greater than the strongest hurricane . Acting on the human body, the shock waves cause pressure waves through the tissues. These waves mostly damage junctions between tissues of different densities (bone and muscle) or the interface between tissue and air. Lungs and

13280-420: The blast's normally invisible shock wave in the moments following the explosion. The heat and airborne debris created by a nuclear explosion can cause rain; the debris is thought to do this by acting as cloud condensation nuclei . During the city firestorm which followed the Hiroshima explosion, drops of water were recorded to have been about the size of marbles . This was termed black rain and has served as

13440-461: The bomb case. Building a bomb case of materials which transmitted rather than absorbed the neutrons could make the bomb more intensely lethal to humans from prompt neutron radiation. This is one of the features used in the development of the neutron bomb . The seismic pressure waves created from an explosion may release energy within nearby plates or otherwise cause an earthquake event. An underground explosion concentrates this pressure wave, and

13600-470: The bombing campaign to be further escalated. Aircraft flying from Allied aircraft carriers and the Ryukyu Islands also regularly struck targets in Japan during 1945 in preparation for Operation Downfall. Firebombing switched to smaller cities, with populations ranging from 60,000 to 350,000. According to Yuki Tanaka , the U.S. fire-bombed over a hundred Japanese towns and cities. The Japanese military

13760-624: The burning of combustible material. Fire experts suggest that unlike Hiroshima, due to the nature of modern U.S. city design and construction, a firestorm in modern times is unlikely after a nuclear detonation. This does not exclude fires from being started but means that these fires will not form into a firestorm, due largely to the differences between modern building materials and those used in World War II-era Hiroshima. There are two types of eye injuries from thermal radiation: flash blindness and retinal burn . Flash blindness

13920-442: The chance that one of them might be a dud. If the test were made on some neutral territory, it was hard to believe that Japan's determined and fanatical military men would be impressed. If such an open test were made first and failed to bring surrender, the chance would be gone to give the shock of surprise that proved so effective. On the contrary, it would make the Japanese ready to interfere with an atomic attack if they could. Though

14080-426: The city and 267,000 buildings in a single night. It was the deadliest bombing raid of the war, at a cost of 20 B-29s shot down by flak and fighters. By May, 75 percent of bombs dropped were incendiaries designed to burn down Japan's "paper cities". By mid-June, Japan's six largest cities had been devastated. The end of the fighting on Okinawa that month provided airfields even closer to the Japanese mainland, allowing

14240-410: The corresponding free electrons. The system then immediately emits electromagnetic (thermal) radiation, the nature of which is determined by the temperature. Since this is of the order of 10 degrees, most of the energy emitted within a microsecond or so is in the soft X-ray region. Because temperature depends on the average internal energy/heat of the particles in a certain volume, internal energy or heat

14400-414: The damage to modern urban areas has found that most scaling laws are too simplistic and tend to overestimate nuclear explosion effects. The scaling laws that were used to produce the table below assume (among other things) a perfectly level target area, no attenuating effects from urban terrain masking (e.g. skyscraper shadowing), and no enhancement effects from reflections and tunneling by city streets. As

14560-411: The dead were civilians. Scholars have extensively studied the effects of the bombings on the social and political character of subsequent world history and popular culture , and there is still much debate concerning the ethical and legal justification for the bombings. According to supporters, the atomic bombings were necessary to bring an end to the war with minimal casualties and ultimately prevented

14720-519: The defense of all of southern Japan, and was located in Hiroshima Castle . Hata's command consisted of some 400,000 men, most of whom were on Kyushu where an Allied invasion was correctly anticipated. Also present in Hiroshima were the headquarters of the 59th Army , the 5th Division and the 224th Division , a recently formed mobile unit. The city was defended by five batteries of 70 mm and 80 mm (2.8 and 3.1 inch) anti-aircraft guns of

14880-451: The effect of being indoors is Akiko Takakura. Despite the lethal radiation and blast zone extending well past her position at Hiroshima, Takakura survived the effects of a 16 kt atomic bomb at a distance of 300 metres (980 ft) from the hypocenter, with only minor injuries, due mainly to her position in the lobby of the Bank of Japan, a reinforced concrete building, at the time. In contrast,

15040-404: The electrons are removed entirely from the atoms, thus causing ionization. Others are raised to higher energy (or excited) states while still remaining attached to the nuclei. Within an extremely short time, perhaps a hundredth of a microsecond or so, the weapon residues consist essentially of completely and partially stripped (ionized) atoms, many of the latter being in excited states, together with

15200-408: The energy released from a nuclear weapon detonated within the lower atmosphere can be approximately divided into four basic categories: Depending on the design of the weapon and the location in which it is detonated, the energy distributed to any one of these categories may be significantly higher or lower. The physical blast effect is created by the coupling of immense amounts of energy, spanning

15360-535: The energy released in the explosion, depending on the yield of the device. In urban areas, the extinguishing of fires ignited by thermal radiation may matter little, as in a surprise attack fires may also be started by blast-effect-induced electrical shorts, gas pilot lights, overturned stoves, and other ignition sources, as was the case in the breakfast-time bombing of Hiroshima. Whether or not these secondary fires will in turn be snuffed out as modern noncombustible brick and concrete buildings collapse in on themselves from

15520-464: The entire war. In February 1945, Prince Fumimaro Konoe advised Emperor Hirohito that defeat was inevitable, and urged him to abdicate. Even before the surrender of Nazi Germany on 8 May 1945, plans were underway for the largest operation of the Pacific War, Operation Downfall , the Allied invasion of Japan. The operation had two parts: set to begin in October 1945, Operation Olympic involved

15680-417: The explosion. The height of burst and apparent size of the fireball, a function of yield and range will determine the degree and extent of retinal scarring. A scar in the central visual field would be more debilitating. Generally, a limited visual field defect, which will be barely noticeable, is all that is likely to occur. When thermal radiation strikes an object, part will be reflected, part transmitted, and

15840-429: The final adjustments of the bomb the Japanese defenders should attack, a faulty move might easily result in some kind of failure. Such an end to an advertised demonstration of power would be much worse than if the attempt had not been made. It was now evident that when the time came for the bombs to be used we should have only one of them available, followed afterwards by others at all-too-long intervals. We could not afford

16000-408: The following fireball, as they may superheat nearby air and/or other material. The vast majority of the energy that goes on to form the fireball is in the soft X-ray region of the electromagnetic spectrum, with these X-rays being produced by the inelastic collisions of the high-speed fission and fusion products. It is these reaction products and not the gamma rays which contain most of the energy of

16160-561: The government position. Japan's willingness to surrender remained conditional on the preservation of the kokutai (Imperial institution and national polity ), assumption by the Imperial Headquarters of responsibility for disarmament and demobilization, no occupation of the Japanese Home Islands , Korea or Formosa , and delegation of the punishment of war criminals to the Japanese government. At Potsdam, Truman agreed to

16320-454: The greatest psychological effect against Japan and (2) making the initial use sufficiently spectacular for the importance of the weapon to be internationally recognized when publicity on it is released.   ... Kyoto has the advantage of the people being more highly intelligent and hence better able to appreciate the significance of the weapon. Hiroshima has the advantage of being such a size and with possible focussing from nearby mountains that

16480-451: The group is exposed to 60 to 180 rems, 50% will become sick with radiation poisoning . If medically treated, all of the 60–180 rems group will survive. If the group is exposed to 200 to 450 rems, most if not all of the group will become sick; 50% will die within two to four weeks, even with medical attention. If the group is exposed to 460 to 600 rems, 100% of the group will get radiation poisoning, and 50% will die within one to three weeks. If

16640-466: The group is exposed to 600 to 1000 rems, 50% will die in one to three weeks. If the group is exposed to 1,000 to 5,000 rems, 100% of the group will die within 2 weeks. At 5,000 rems, 100% of the group will die within 2 days. Researchers from the University of Nicosia simulated, using high-order computational fluid dynamics , an atomic bomb explosion from a typical intercontinental ballistic missile and

16800-565: The home islands area in April, May and June 1945. While the Japanese military decided to resume attacks on Allied bombers from late June, by this time there were too few operational fighters available for this change of tactics to hinder the Allied air raids. The discovery of nuclear fission in 1938 made the development of an atomic bomb a theoretical possibility. Fears that a German atomic bomb project would develop atomic weapons first, especially among scientists who were refugees from Nazi Germany and other fascist countries, were expressed in

16960-484: The home islands, backed by a civilian militia of 28 million. Casualty predictions varied widely, but were extremely high. The Vice Chief of the Imperial Japanese Navy General Staff , Vice Admiral Takijirō Ōnishi , predicted up to 20 million Japanese deaths. The Americans were alarmed by the Japanese buildup, which was accurately tracked through Ultra intelligence. On 15 June 1945,

17120-596: The industrial buildings were also built around timber frames. The city as a whole was highly susceptible to fire damage. It was the second largest city in Japan after Kyoto that was still undamaged by air raids, primarily because it lacked the aircraft manufacturing industry that was the XXI Bomber Command's priority target. On 3 July, the Joint Chiefs of Staff placed it off limits to bombers, along with Kokura, Niigata and Kyoto. The population of Hiroshima had reached

17280-438: The initial gamma radiation includes that arising from these reactions as well as that resulting from the decay of short-lived fission products. The intensity of initial nuclear radiation decreases rapidly with distance from the point of burst because the radiation spreads over a larger area as it travels away from the explosion (the inverse-square law ). It is also reduced by atmospheric absorption and scattering. The character of

17440-466: The leader of the world for the common welfare cannot drop that terrible bomb on the old capital [Kyoto] or the new [Tokyo]. He and I are in accord. The target will be a purely military one. The 16 July success of the Trinity Test in the New Mexico desert exceeded expectations. On 26 July, Allied leaders issued the Potsdam Declaration , which outlined the terms of surrender for Japan. The declaration

17600-431: The light hydrogen nuclei (protons) predominating in the exploded TNT molecules (surrounding the core of Fat Man) slowed down neutrons very efficiently while the heavier iron atoms in the steel nose forging of Little Boy scattered neutrons without absorbing much neutron energy. It was found in early experimentation that normally most of the neutrons released in the cascading chain reaction of the fission bomb are absorbed by

17760-429: The many buildings on the flat terrain at Hiroshima. As thermal radiation travels more or less in a straight line from the fireball (unless scattered), any opaque object will produce a protective shadow that provides protection from the flash burn. Depending on the properties of the underlying surface material, the exposed area outside the protective shadow will be either burnt to a darker color, such as charring wood, or

17920-437: The material is a poor thermal conductor, the heat is confined to the surface of the material. The actual ignition of materials depends on how long the thermal pulse lasts and the thickness and moisture content of the target. Near ground zero where the energy flux exceeds 125 J /cm , what can burn, will. Farther away, only the most easily ignited materials will flame. Incendiary effects are compounded by secondary fires started by

18080-459: The matter. Truman agreed with Stimson, and Kyoto was temporarily removed from the target list. Groves attempted to restore Kyoto to the target list in July, but Stimson remained adamant. On 25 July, Nagasaki was put on the target list in place of Kyoto. It was a major military port, one of Japan's largest shipbuilding and repair centers, and an important producer of naval ordnance. In early May 1945,

18240-470: The meetings on 31 May and 1 June, scientist Ernest Lawrence had suggested giving the Japanese a non-combat demonstration. Arthur Compton later recalled that: It was evident that everyone would suspect trickery. If a bomb were exploded in Japan with previous notice, the Japanese air power was still adequate to give serious interference. An atomic bomb was an intricate device, still in the developmental stage. Its operation would be far from routine. If during

18400-421: The missions over Japan were flown by single unescorted bombers with a single payload to accustom the Japanese to this pattern. They also simulated actual atomic bombing runs, including the directions of ingress and egress with respect to the wind. Tibbets himself was barred from flying most missions over Japan for fear that he might be captured and interrogated. On 5 April 1945, the code name Operation Centerboard

18560-573: The modelling of the high-frequency (>4 Hz) teleseismic P wave amplitudes. However, theory does not suggest that a nuclear explosion of current yields could trigger fault rupture and cause a major quake at distances beyond a few tens of kilometers from the shot point. The following table summarizes the most important effects of single nuclear explosions under ideal, clear skies, weather conditions. Tables like these are calculated from nuclear weapons effects scaling laws. Advanced computer modelling of real-world conditions and how they impact on

18720-418: The multi-megaton range. This is because the intensity of the blast effects drops off with the third power of distance from the explosion, while the intensity of radiation effects drops off with the second power of distance. This results in the range of thermal effects increasing markedly more than blast range as higher and higher device yields are detonated. Thermal radiation accounts for between 35 and 45% of

18880-523: The nature of explosions. For air bursts at or near sea level, 50–60% of the explosion's energy goes into the blast wave , depending on the size and the yield of the bomb . As a general rule, the blast fraction is higher for low yield weapons. Furthermore, it decreases at high altitudes because there is less air mass to absorb radiation energy and convert it into a blast. This effect is most important for altitudes above 30  km, corresponding to less than 1 percent of sea-level air density. The effects of

19040-419: The nuclear reactions in the form of kinetic energy. This kinetic energy of the fission and fusion fragments is converted into internal and then radiation energy by approximately following the process of blackbody radiation emitting in the soft X-ray region. As a result of numerous inelastic collisions, part of the kinetic energy of the fission fragments is converted into internal and radiation energy. Some of

19200-615: The only way to destroy their production capabilities, shifting from precision bombing to area bombardment with incendiaries. Like most strategic bombing during World War II , the aim of the air offensive against Japan was to destroy the enemy's war industries, kill or disable civilian employees of these industries, and undermine civilian morale . Over the next six months, the XXI Bomber Command under LeMay firebombed 64 Japanese cities. The firebombing of Tokyo , codenamed Operation Meetinghouse , on 9–10 March, killed an estimated 100,000 people and destroyed 41 km (16 sq mi) of

19360-587: The possibility of a demonstration that would not destroy human lives was attractive, no one could suggest a way in which it could be made so convincing that it would be likely to stop the war. The possibility of a demonstration was raised again in the Franck Report issued by physicist James Franck on 11 June and the Scientific Advisory Panel rejected his report on 16 June, saying that "we can propose no technical demonstration likely to bring an end to

19520-400: The psychological impact of bombing, and reduce the international stigma of area-bombing cities. Even with the warnings, Japanese opposition to the war remained ineffective. In general, the Japanese regarded the leaflet messages as truthful, with many Japanese choosing to leave major cities. The leaflets caused such concern that the government ordered the arrest of anyone caught in possession of

19680-433: The purpose by Philip Morrison . Magnesium was chosen because it does not act as a neutron reflector . The core departed from Kirtland Army Air Field on a C-54 transport aircraft of the 509th Composite Group's 320th Troop Carrier Squadron on 26 July, and arrived at North Field 28 July. Three Fat Man high-explosive pre-assemblies, designated F31, F32, and F33, were picked up at Kirtland on 28 July by three B-29s, two from

19840-474: The radiation received at a given location also varies with the distance from the explosion. Near the point of the explosion, the neutron intensity is greater than the gamma intensity, but with increasing distance the neutron-gamma ratio decreases. Ultimately, the neutron component of the initial radiation becomes negligible in comparison with the gamma component. The range for significant levels of initial radiation does not increase markedly with weapon yield and, as

20000-431: The reaction until all the world's atmospheric nitrogen was consumed. Hans Bethe was assigned to study this hypothesis from the project's earliest days, and he eventually concluded that such a reaction could not sustain itself on a large scale due to cooling of the nuclear fireball through an inverse Compton effect. Richard Hamming was asked to make a similar calculation just before the first nuclear test , and he reached

20160-420: The rest absorbed. The fraction that is absorbed depends on the nature and color of the material. A thin material may transmit most of the radiation. A light-colored object may reflect much of the incident radiation and thus escape damage, like anti-flash white paint. The absorbed thermal radiation raises the temperature of the surface and results in scorching, charring, and burning of wood, paper, fabrics, etc. If

20320-506: The resulting blast wave to see how it would affect people sheltering indoors. They found that the blast wave was enough in the moderate damage zone to topple some buildings and injure people caught outdoors. However, sturdier buildings, such as concrete structures, can remain standing. The team used advanced computer modelling to study how a nuclear blast wave speeds through a standing structure. Their simulated structure featured rooms, windows, doorways, and corridors and allowed them to calculate

20480-408: The same blast wave is uncertain, not least of which, because of the masking effect of modern city landscapes on thermal and blast transmission are continually examined. When combustible frame buildings were blown down in Hiroshima and Nagasaki, they did not burn as rapidly as they would have done had they remained standing. The noncombustible debris produced by the blast frequently covered and prevented

20640-431: The same conclusion. Nevertheless, the notion has persisted as a rumor for many years and was the source of apocalyptic gallows humor at the Trinity test where Enrico Fermi took side bets on atmospheric ignition. Survivability is highly dependent on factors such as if one is indoors or out, the size of the explosion, the proximity to the explosion, and to a lesser degree the direction of the wind carrying fallout. Death

20800-416: The same precision bombing tactics, with equally unsatisfactory results. The attacks initially targeted key industrial facilities but much of the Japanese manufacturing process was carried out in small workshops and private homes. Under pressure from United States Army Air Forces (USAAF) headquarters in Washington, LeMay changed tactics and decided that low-level incendiary raids against Japanese cities were

20960-428: The similar naming can be confusing. About 5% of the energy released in a nuclear air burst is in the form of ionizing radiation : neutrons , gamma rays, alpha particles and electrons moving at speeds up to the speed of light. Gamma rays are high-energy electromagnetic radiation; the others are particles that move slower than light. The neutrons result almost exclusively from the fission and fusion reactions, while

21120-439: 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; Yokohama , an urban center for aircraft manufacture, machine tools, docks, electrical equipment and oil refineries; Niigata , a port with industrial facilities including steel and aluminum plants and an oil refinery; and Kyoto , a major industrial center. The target selection

21280-408: The slant/horizontal range of a nuclear explosion, during fog or haze conditions. So despite any object that casts a shadow being rendered ineffective as a shield from the flash by fog or haze, due to scattering, the fog fills the same protective role, but generally only at the ranges that survival in the open is just a matter of being protected from the explosion's flash energy. The thermal pulse also

21440-567: The source of a book and film by the same name . Black rain is not unusual following large fires and is commonly produced by pyrocumulus clouds during large forest fires. The rain directly over Hiroshima on that day is said to have begun around 9 a.m. with it covering a wide area from the hypocenter to the northwest, raining heavily for one hour or more in some areas. The rain directly over the city may have carried neutron activated building material combustion products, but it did not carry any appreciable nuclear weapon debris or fallout, although this

21600-478: The spot. Along with Captain William S. Parsons , the commander of Project Alberta, they became known as the "Tinian Joint Chiefs". In April 1945, Marshall asked Groves to nominate specific targets for bombing for final approval by himself and Stimson. Groves formed a Target Committee, chaired by himself, that included Farrell, Major John A. Derry, Colonel William P. Fisher, Joyce C. Stearns and David M. Dennison from

21760-400: The start of August, and they cost billions of dollars, so using one for a demonstration would be expensive. For several months, the U.S. had warned civilians of potential air raids by dropping more than 63 million leaflets across Japan. Many Japanese cities suffered terrible damage from aerial bombings; some were as much as 97 percent destroyed. LeMay thought that leaflets would increase

21920-418: The surrounding medium to make a spherically expanding shock wave . At first, this shock wave is inside the surface of the developing fireball, which is created in a volume of air heated by the explosion's "soft" X-rays. Within a fraction of a second, the dense shock front obscures the fireball and continues to move past it, expanding outwards and free from the fireball, causing a reduction of light emanating from

22080-449: The total effect of nuclear blasts on the ozone layer have been at least tentatively exonerating after initial discouraging findings. Gamma rays from a nuclear explosion produce high energy electrons through Compton scattering . For high altitude nuclear explosions, these electrons are captured in the Earth's magnetic field at altitudes between 20 and 40 kilometers where they interact with

22240-425: The uncertainty of a successful detonation and also because of the wish to maximize shock in the leadership . No warning was given to Hiroshima that a new and much more destructive bomb was going to be dropped. Various sources gave conflicting information about when the last leaflets were dropped on Hiroshima prior to the atomic bomb. Robert Jay Lifton wrote that it was 27 July, and Theodore H. McNelly wrote that it

22400-571: The underground explosion may have launched a metal cover plate into space at six times Earth's escape velocity , although the evidence remains subject to debate. In 1942, there was speculation among the scientists developing the first nuclear weapons in the Manhattan Project that a sufficiently large nuclear explosion might ignite the Earth's atmosphere: heat from the explosion might fuse pairs of atmospheric nitrogen atoms, forming carbon and oxygen while releasing further energy which would sustain

22560-512: The unknown person sitting outside, fully exposed, on the steps of the Sumitomo Bank , next door to the Bank of Japan, received lethal third-degree burns and was then likely killed by the blast, in that order, within two seconds. With medical attention, radiation exposure is survivable to 200 rems of acute dose exposure. If a group of people is exposed to a 50 to 59 rems acute (within 24 hours) radiation dose, none will get radiation sickness. If

22720-509: The use of a weapon that 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 MacArthur ensured that Chemical Warfare Service units were trained in their use. Consideration

22880-408: The use of atomic bombs on Germany as soon as possible, but was informed the first usable atomic weapons were still months away. America's reserves of manpower were running out. Deferments for groups such as agricultural workers were tightened, and there was consideration of drafting women. At the same time, the public was becoming war-weary, and demanding that long-serving servicemen be sent home. In

23040-402: The visual pigments and temporary blindness for up to 40 minutes. A retinal burn resulting in permanent damage from scarring is also caused by the concentration of direct thermal energy on the retina by the lens. It will occur only when the fireball is actually in the individual's field of vision and would be a relatively uncommon injury. Retinal burns may be sustained at considerable distances from

23200-433: The war, reached disastrous levels by the middle of 1945. The loss of shipping also affected the fishing fleet, and the 1945 catch was only 22 percent of that in 1941. The 1945 rice harvest was the worst since 1909, and hunger and malnutrition became widespread. U.S. industrial production was overwhelmingly superior to Japan's. By 1943, the U.S. produced almost 100,000 aircraft a year, compared to Japan's production of 70,000 for

23360-405: The war; we see no acceptable alternative to direct military use." Franck then took the report to Washington, D.C., where the Interim Committee met on 21 June to re-examine its earlier conclusions; but it reaffirmed that there was no alternative to the use of the bomb on a military target. Like Compton, many U.S. officials and scientists argued that a demonstration would sacrifice the shock value of

23520-414: The weapon and also depends on the burst altitude. Contrary to what might be expected from geometry, the blast range is not maximal for surface or low altitude blasts but increases with altitude up to an "optimum burst altitude" and then decreases rapidly for higher altitudes. This is caused by the nonlinear behavior of shock waves. When the blast wave from an air burst reaches the ground it is reflected. Below

23680-469: The work was accelerated, first as a pilot program, and finally in the agreement by Roosevelt to turn the work over to the U.S. Army Corps of Engineers to construct the production facilities necessary to produce uranium-235 and plutonium-239 . This work was consolidated within the newly created Manhattan Engineer District, which became better known as the Manhattan Project , eventually under the direction of Major General Leslie R. Groves, Jr. . The work of

23840-427: Was 30 July. The USAAF history noted that eleven cities were targeted with leaflets on 27 July, but Hiroshima was not one of them, and there were no leaflet sorties on 30 July. Leaflet sorties were undertaken on 1 and 4 August. Hiroshima may have been leafleted in late July or early August, as survivor accounts talk about a delivery of leaflets a few days before the atomic bomb was dropped. Three versions were printed of

24000-529: Was also given to using biological weapons . While the United States 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 Chengdu in China to make

24160-492: Was assigned. The officer responsible for its allocation in the War Department 's Operations Division was not cleared to know any details of it. The first bombing was later codenamed Operation Centerboard I, and the second, Operation Centerboard II. The 509th Composite Group had an authorized strength of 225 officers and 1,542 enlisted men, almost all of whom eventually deployed to Tinian. In addition to its authorized strength,

24320-467: Was carried out. Two different types of bombs were eventually developed: a gun-type fission weapon that used uranium-235, called Little Boy , and a more complex implosion-type nuclear weapon that used plutonium-239, called Fat Man . There was a Japanese nuclear weapon program , but it lacked the human, mineral, and financial resources of the Manhattan Project, and never made much progress towards developing an atomic bomb. The 509th Composite Group

24480-551: Was chosen to allow for Olympic to complete its objectives, for troops to be redeployed from Europe, and the Japanese winter to pass. Japan's geography made this invasion plan obvious to the Japanese; they were able to predict the Allied invasion plans accurately and thus adjust their defensive plan, Operation Ketsugō , accordingly. The Japanese planned an all-out defense of Kyūshū, with little left in reserve. In all, there were 2.3 million Japanese Army troops prepared to defend

24640-468: Was completed on 15 June, and the target insert on 24 July. The projectile and eight bomb pre-assemblies (partly assembled bombs without the powder charge and fissile components) left Hunters Point Naval Shipyard , California, on 16 July aboard the cruiser USS  Indianapolis , and arrived on Tinian on 26 July. The target insert followed by air on 30 July, accompanied by Commander Francis Birch from Project Alberta. Responding to concerns expressed by

24800-449: Was constituted on 9 December 1944, and activated on 17 December 1944, at Wendover Army Air Field , Utah, commanded by Colonel Paul Tibbets . Tibbets was assigned to organize and command a combat group to develop the means of delivering an atomic weapon against targets in Germany and Japan. Because the flying squadrons of the group consisted of both bomber and transport aircraft, the group

24960-456: Was designated as a "composite" rather than a "bombardment" unit. Due to its remoteness, Tibbets selected Wendover for his training base over Great Bend, Kansas and Mountain Home, Idaho . Each bombardier completed at least 50 practice drops of inert or conventional explosive pumpkin bombs , targeting islands around Tinian and later the Japanese home islands, until as late as 14 August 1945. Some of

25120-773: Was likely stripped for spare parts and later abandoned. Before the aircraft was recovered, its propeller blade was cut off, with its engine cowling and cockpit canopy was missing. The aircraft was recovered from Babo airfield in 1987, was restored and then displayed with Indonesian Air Force markings at the Dirgantara Mandala Museum. Data from Japanese Aircraft of the Pacific War General characteristics Performance Armament Aircraft of comparable role, configuration, and era Related lists Atomic bombings of Hiroshima and Nagasaki Second Sino-Japanese War On 6 and 9 August 1945,

25280-476: 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". The atomic bomb was not mentioned in the communiqué. On 28 July, Japanese papers reported that the declaration had been rejected by the Japanese government. That afternoon, Prime Minister Kantarō Suzuki declared at

25440-464: Was subject to the following criteria: These cities were largely untouched during the nightly bombing raids, and the Army Air Forces agreed to leave them off the target list so accurate assessment of the damage caused by the atomic bombs 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

25600-523: Was unable to stop the Allied attacks and the country's civil defense preparations proved inadequate. Japanese fighters and anti-aircraft guns had difficulty engaging bombers flying at high altitude. From April 1945, the Japanese interceptors also had to face American fighter escorts based on Iwo Jima and Okinawa. That month, the Imperial Japanese Army Air Service and Imperial Japanese Navy Air Service stopped attempting to intercept

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