80th Anniversary of the Atomic Bombings: Revisiting the Record

In this memorandum, Robert Oppenheimer discussed the consequences of an air burst of an atomic weapon and the precautions that the bomber crew needed to take. The weapon was composed of toxic material, and the explosion would emit radiation that would be “injurious within a mile” and “lethal within a radius of about six-tenths of a mile.” Moreover, “most of the [radioactive] activity will rise to a considerable height above the target and will remain as a fairly compact cloud for a period of hours after the detonation.” Because of that danger, he recommended safety measures for aircrews to take after the detonation. Oppenheimer did not mention any possibility that the bomb could produce radiation sickness, but he was aware of the problem.[17]

The experience of the Trinity detonation influenced Stafford Warren’s report to Groves about the military use of the “gadget.” (MED officials referred to a “gadget,” instead of a bomb, partly for security reasons but perhaps also to “ease their minds” about the purposes of their work[18] Warren discussed the impact of an explosion over a city, ranging from the radiation hazards to the production of fires. The fireball would require pilots to use special goggles to protect their eyes, and the radiation produced by the bomb could endanger troops entering a city after an explosion. Warren was giving advice on how to use the “gadget” as an “assault weapon,” and he recommended specific tactics to do so. At the end of the memo, Warren included a chart showing the dangers to “normal active troops” in terms of levels of exposure and the possibility of injuries. The range of exposure was from 30 to 500 roentgen, depending on how long a person was in the danger zone. At the highest levels of exposure, Warren estimated that many troops could experience “permanent damage.”

Groves’ report to General Marshall on Trinity emphasized blast effects but made a strikingly misleading statement about radiation effects, especially in light of what Stafford Warren had already written to him (Document 10). As Sean Malloy has noted, when Groves wrote that “No damaging effects are anticipated on the ground from radioactive materials,” he “stripped away virtually all of Warren's caveats and precautions (as well as his estimates of safe and unsafe dosages for occupying troops)."[19]

A few days after the Hiroshima bombing, Harold Jacobson, a New York City-based scientist who had briefly worked for the MED, wrote a widely distributed report, first published in the San Francisco Examiner, asserting erroneously and sensationally that the radiation would render Hiroshima uninhabitable for 70 years. Groves telephoned Oppenheimer about Jacobson’s article. Oppenheimer had not seen it and said “this is of course lunacy.” Oppenheimer also said that “based on the test in New Mexico there would be no appreciable activity on the ground and what little there was would decay very rapidly.” He authorized Groves to use that statement.

Under pressure from federal agents, Jacobson disowned his report, but it received wide publicity and reached Japanese audiences very quickly, on whom it had a significant impact.[20]

Soon after the atomic bombings, Robert Stone, director of the health division at the Metlab, expressed concern about radiation effects in a letter to a former student, Hymer Friedell, Stafford Warren’s deputy based at Site X. Wondering whether the “Japanese were warned that radiation hazards would remain after the explosion hazard had passed away,” Stone worried that health workers would be dangerously exposed. He wrote that failure to warn raised the possibility of guilt for the “unnecessary destruction of life.” Especially distressing to him was Oppenheimer’s response to the Jacobson report (as quoted above). “I could hardly believe my eyes when I saw a news release said to be quoting Oppenheimer and giving the impression that there is no radioactive hazard. Apparently all things are relative.”

A few days after the bombing of Nagasaki, a report from persons unknown went to General Groves on the “toxic effects” of the bomb. With Groves’ aversion to associating the idea of toxins and poisons with the bomb, he may have disliked this report, if he read it. It described in detail the creation of fallout and the biological impact of radiation doses at various levels and periods of time. It is possible that the report was prepared as background for Groves’ decision to approve the dispatch of a survey team to Japan to assess the damage and determine safety conditions before U.S. occupation troops arrived. In that connection, the table on page 4 concerning levels of exposure is similar to the table on page 3 of Stafford Warren’s memo to Groves on 25 July (see Document 2).

With Japan’s surrender expected, the U.S. high command accelerated planning for the occupation. Marshall informed Gen. Douglas MacArthur that Gen. Groves had directed MED officials on Tinian (where they had supervised the atomic bombing operations), to send investigative groups to Hiroshima and Nagasaki to assess the impact of the bombings and to determine whether conditions there were safe enough to admit U.S. forces. In addition, Groves wanted Farrell to send a team to Tokyo to check the status of Japanese nuclear research. When Japan surrendered, moving these plans forward became a complex task because the teams required optimum numbers of scientific and technical experts. By 5 September the first group had arrived in Japan.[21]

Reminding Marshall that he had sent “teams of investigators” to Japan, Groves further informed him in this memo that he wanted the teams to determine the impact of radioactivity on the Japanese. He believed that Japanese casualties from radiation were “unlikely,” but the “facts” had to be established.

Truman’s announcement that the U.S. had dropped an atomic bomb on Hiroshima enabled Japanese scientists to make sense of reports of casualties with mysterious symptoms that soon emerged in Hiroshima and then Nagasaki. Two scientists at Oak Ridge’s Health Division, Paul Henshaw, a physicist (later a leader of the U.S. Atomic Bomb Casualty Commission [ABCC]), and Robert Coveyou, a mathematician, drew some conclusions about the health effects of the bombings as reported by United Press International: people who had looked healthy became weak “for unknown reasons,” and many died. Henshaw and Coveyou’s review of atomic bomb effects led them to find that “it seems highly plausible that a great many persons were subjected to lethal and sub-lethal dosages of radiation in areas where direct blast effects were possibly non-lethal.” It was “probable,” therefore, that radiation “would produce increments to the death rate and “even more probable” that a “great number of cases of sub-lethal exposures to radiation have been suffered.”[22]

Interested in having the press visit the Trinity test site but concerned about the Japanese reports of radiation sickness, Groves telephoned Louis Hempelmann and asked him about the present level of radioactivity. Groves then requested that Hempelmann write a short memorandum on radioactivity “stating how long it is in the general area covered and showing how it diminishes from time to time.” With respect to the crater, Hempelmann said there was a “fair amount” of radioactivity around it and that it was “fairly intense” for 100 feet (probably from ground zero). When Groves asked if it was safe for reporters to visit, Hempelmann replied that “they wouldn’t be so safe.” Thus, when Groves and Oppenheimer brought reporters to the site on September 11, 1945, everyone in the group wore protective white booties as a safety measure.

Radio broadcasts from Japan reported the effects of radiation sickness, but Gen. Groves and Dr. Charles Rea, a surgeon who was head of the base hospital at Oak Ridge, dismissed them as “propaganda.” Both agreed that the injuries were nothing more than “good thermal burns.” Rea had no specialized knowledge of radiation, but if Groves had read the secret memoranda on that subject that he had received, he may have been speaking disingenuously. Perhaps he was in denial about the radiation and was seeking assurance from Rea. If Groves was worried about the broader implications of bomb-caused radiation sickness, a strategy of denial was a way to protect the new weapon from charges that it, like poison gas, was on the other side of a “crucial moral threshold.”[23] What further upset Groves about the reports from Japan, as he disclosed at the end of the conversation, was that an “American started them off,” referring to the report by Harold Jacobson.

In this memorandum to Oppenheimer, George B. Kistiakowsky, who led explosives research at Los Alamos, reviewed pending issues, including the expansion of Los Alamos’s Site-S (which produced special lenses for plutonium bombs) and the future of the “Project.” But he began by briefly recounting the internal discussion over how to respond to Japanese reports about radiation sickness.[24] Kistiakowsky described how, in response to queries from Gen. Groves about the reports, he had teletyped recommendations that the Manhattan Project director had rejected. Kistiakowsky then asked Louis Hempelmann and others to prepare a memorandum for Groves on the effects of the bombings but seems to have hesitated in sending it after Groves said, during a press conference at Oak Ridge, Tennessee, that the accounts from Japan were “propaganda” and that radiation had not caused any deaths.[25] In light of the Hempelmann team’s findings, Kistiakowsky observed that Groves had “stuck his neck out by a mile.” A FOIA request and subsequent appeal to the National Nuclear Security Administration led to the unearthing of the Hempelmann memo [See Document 13, below] but not Kistiakowsky’s teletype.

With U.S. scientists and medical doctors on their way to Japan to study the impact of the bombings, more information and analysis on the impact of radiation would become available, but the results of those investigations would be classified for years, just like this preliminary assessment.

The memo that Kistiakowsky requested but was hesitant to send to Groves – prepared by Victor Weisskopf, Paul Aebersold, Louis H. Hempelmann, and Frederick Reines – did not mention the news reports from Japan about burn injuries and lingering deaths and suffering (thus avoiding any risk of being seen as sympathetic to the Japanese), but the authors estimated that radiation exposure was a probable cause of some fatalities, essentially confirming those accounts.

The four Los Alamos scientists and medical doctors who prepared the memorandum explained how an atomic explosion would have deadly “biological effects,” not only from the blast but also from gamma radiation and thermal energy, with other possible effects, such as those caused by radioactive “dust particles,” not calculable. They presented their findings in a table attached to an explanatory memorandum. For many Los Alamos scientists, this memorandum may have been a reminder of what they already knew.

The writers did not explain their methodology but may have been generalizing from the effects of weapons with an explosive yield in the range of 10 kilotons of T.N.T., which was Enrico Fermi’s initial estimate for the July 16, 1945, Trinity test. Whatever their methodology was, the table developed by the authors showed the impact on the ground metrically in terms of the radius and the distance from ground zero. The avoidance of references to yield estimates may have kept the classification level down.

The authors calculated the deadly impact of the blast itself (“flying debris, falling buildings, violent displacement, etc.”) and the extreme heat, which were the two primary effects contemplated by Los Alamos scientists who developed the bomb.[35] Blast effects were “lethal” within the radius of a half mile to a mile and even further, projecting overpressures of 27 pounds per square inch at 800 meters (about one-half mile) and 23 p.s.i. at 1000 meters (at 0.62 miles). The blast would not kill everyone within the range: “Freak survivals of individuals within this area would certainly occur,” according to the report, such as people who were inside hardened structures.

But those who lived through the initial blast would suffer exposure to “gamma radiation emitted within a few seconds after the explosion,” according to the report, which estimated that levels of 500 to 900 roentgen, found 800 to 900 meters from ground zero, would be lethal. “Freak survivors of the blast within this area would be killed by radiation,” the scientists said, although “death … might be delayed for a period of weeks.” Similarly, a 1945 U.S. Navy report found that people who were inside Hiroshima’s Bankers Club building survived the initial blast but “died later from radiation reaction, due in large part to scattered rays of secondary type.” As the Navy report explained, “This is at first difficult to understand, until one remembers that radiation entering through a window or other opening will strike floor[s] and wells and induce much secondary radiation.”

“Severe thermal burns (third degree) of the exposed skin” were expected within a mile of the blast site, although clothing or even “light shelter” would offer “considerable protection” from them. The “short intense exposure” to thermal radiation meant that the burns, later called “flash burns” were likely to be “even more serious than the most severe sunburns.” The authors used calories for measuring the levels of heat and light that people would experience at various distances. Because 8 calories/CM² was enough to cause third-degree burns, people exposed to 11 calories/CM² at 1400 meters would suffer burns that penetrated one millimeter of skin (the thickness of a credit card).

One incalculable effect was exposure to “radioactive material deposited on the ground.” While the memo said it would probably be “insignificant,” the authors noted the possibility of “unusual meteorological phenomena resulting in local precipitation or deposition of active material on falling dust particles.” Even Oppenheimer, in a statement cited by Dr. Robert Stone [See Document 5], had denied the possibility of radiation on the ground in Hiroshima or Nagasaki, but such effects would continue to be discussed in the media and in classified reports.[26]

Other “biological effects” of the bombings, such as “suffocation” or “burning to death,” could not be predicted, according to the memo. With so much emphasis placed on the blast, radiation, and thermal effects of the bombs, there is little to suggest that anyone predicted that mass fires would cause many deaths in Hiroshima and Nagasaki.

With U.S. scientists and medical doctors soon on their way to Japan to study the impact of the bombings, more information and analysis on the effects of radiation would become available, but the results of those investigations would be classified for years, just like this preliminary assessment.

In several conversations on September 7 Groves continued to dismiss reports of Japanese deaths from radiation effects. Speaking with Harvard University President James B. Conant, who was also a top Manhattan Project official, Groves said there was “no basis” to reports of deaths from radiation, but said that Col. Stafford Warren, the chief medical officer, was going to Japan to look into the problem. Groves also had a conversation with Dr. Charles Rea, head of the Oak Ridge base hospital, who explained to him the difference between leukemia, an increase in white blood cells, and leukopenia, a decrease in white cells that was experienced by people exposed to radiation effects.

Groves mentioned a document discussing “three different causes of casualties,” possibly a reference to the recent Los Alamos memorandum (which may have eventually reached Groves, despite Kistiakowsky’s hesitations). When Groves asked whether “diet” could be a cause of leukopenia, Rea said it wasn’t but suggested that “it could be caused by some medicines like benzidrine [sic].” As in an earlier conversation [See Document 11], Rea believed that post-explosion deaths in Japan were caused by “heat” but he added that deaths that occurred later “could be caused from the blast,” noting, for example, the cases of “people who are in accidents and who walk away apparently unharmed and die the next day.”

Speaking with Oppenheimer later that morning, it was evident that Groves bought into Rea’s story and not the findings of the Los Alamos staff. When Oppenheimer mentioned “delayed effects from radiation,” Groves said that Rea had accounted for the deaths as “delayed heat and blast cases.” On that, Oppenheimer made no comment. Groves would eventually accept that delayed radiation effects caused deaths [See Document 21].

With Groves seeking information that would refute the accounts of radiation sickness, General Farrell sent back reports that deemphasized the radiation problem. While recognizing that the “Japanese reports … are essentially correct, as to clinical effects from single gamma radiation dose,” Farrell qualified that statement by reporting that Stafford Warren found that only a “small percentage of injured survivors” had radiation sickness. He did not mention that when meeting with the U.S. and international press in Tokyo, he had derided accounts of radiation sickness as “Japanese propaganda.” Farrell also reported that “Warren found no measurable radioactivity on preliminary measurements under detonation site or elsewhere on ground, streets, ashes or other materials.” In fact, however, Warren and James Nolan were finding a “very slight amount of radioactivity on the ground.”[27]

When U.S. officials faced media reports of Japanese radiation sickness, they continued the denial approach. On 7 September, U.S. occupation authorities in Tokyo held a press conference after Australian reporter Wilfred Burchett published a story in the British Daily Express, “The Atomic Plague,” based on his visit to Hiroshima a few days earlier. The purpose of the briefing, led by General Farrell, was to deny the story. Burchett arrived near the end of the briefing; according to his account, when he declared that he had witnessed the harmful impact of radiation exposure (although he did not use those words), the general declared that he was a “victim [of] Japanese propaganda.” Farrell brought the briefing to an end.[28]

The next week, Farrell held a press briefing that began with a statement downplaying the radiation danger. Farrell asserted that “no measurable radioactivity [was] found under the point of detonation or elsewhere on the ground, streets, in the ashes or on other materials.” Citing Stafford Warren, he further asserted that “patients who were effected by radiation resulted from a single exposure to a dose of gamma radiation at the time of detonation” not from “deposit of dangerous amounts of radioactivity on the ground.” Equivocating a bit, Farrell declared that it was “not the whole truth … that personnel coming into the area to assist in evacuation were seriously injured.” It was “the opinion of our experts that there would be no residual radioactivity on the ground in dangerous amounts.” Although residual radiation would dissipate, those claims were doubtful because Japanese volunteers who helped with recovery efforts during the days after the detonations experienced radiation sickness.[29]

In this follow-up report on the destruction, Farrell focused on the blast damage. Without referring specifically to radiation, he cited Japanese reports that “anyone who entered the blast area from outside after the explosion has become sick.” Farrell’s report also included this information concerning Nagasaki from Japanese officials: “a number have died up to September 1st who did not seem to be wounded originally” and that “each day about twenty wounded were dying.”

One of the witnesses to the attack on Hiroshima that members of the U.S. survey team met was Johannes Siemes, a German Jesuit priest and a Ph.D. historian who taught philosophy at Sophia University.[30] Escaping firebombed Tokyo, Siemes traveled to Hiroshima where he stayed in a Jesuit novitiate located in a nearby suburb, Nagatsuke. According to his eyewitness account, he felt the immediate blast effects of the bomb and witnessed the mass fires, the devastation and the human toll, which he tried to alleviate with the scant resources that were available. Noting that Japanese newspapers were reporting on an “atomic bomb,” Siemes discussed the connections between radiation sickness and the “gamma rays that had been sent out” by the explosion: there “seems to be some truth in the statement that the radiation had some effect on the blood” (an article published by Siemes in 1946 was more definitive on the relationship).[31]

During the weeks after the attack, Siemes wrote a moving account of his experience that he provided to Stafford Warren (under unclear circumstances), who took it to Dr. Averill Liebow, one of the members of the U.S. survey team. A U.S. immigrant, Liebow spoke German and on 27 September 1945 translated Siemes’ account, dictating it to a U.S. Army sergeant who typed it up. Liebow later modestly wrote that his translation “did less than full justice … to the style, excitement, and literary merit of the original German.”[32] When Stafford Warren sent a secret report to General Groves on the effects of the atomic bombings, he included a copy of the translation “for its value as background material” [See Document 19].[33]

Siemes’ account led the U.S. doctors to another priest, Wilhelm Kleinsorge, who had been in Hiroshima and was in a Tokyo hospital suffering from radiation sickness. He may have been the first such patient that the U.S. doctors met. Later, when the journalist John Hersey visited Tokyo to research the atomic bombings, he acquired a copy of Siemes’ narrative, which had a significant impact on the article that he published in The New Yorker.[34]

For its historical interest and importance, this is very likely an original, or certainly a very early copy, of Liebow’s translation as dictated in September 1945. This rendition is not wholly legible, however, and tidier versions of Siemes’ account are available, such as this online version, in the nicely typed format that went to General Groves, but also in the 1946 MED public report on the atomic bombings. Why Siemes’ report attracted such interest among U.S. officials is worth considering; such aspects as his straightforward narration, his raising of philosophical questions, and his European background may have been elements.

After returning from Japan, Warren, with the assistance of James F. Nolan, prepared a detailed preliminary report on the results of the atomic attacks on Hiroshima and Nagasaki. More information would be gleaned by the Navy’s team and later through the preparation of the report by the U.S.-Japan “Joint Commission of the Investigation of the Effects of the Atomic Bomb in Japan.” Even more data would be gathered by the Joint Commission’s successor, the Atomic Bomb Casualty Commission.

The report focused on medical findings, radioactivity measurements, and estimates of damage to structures. On casualties, Warren provided detailed information on the kinds of injuries suffered, including thermal burns and those caused by blast effects, and the delayed symptoms of radiation poisoning, which showed up after three to thirty days. He reported that of the “approximately 4000 patients admitted to hospitals [in both cities], 1300 or 33% showed effects of radiation and of this number approximately one-half died.”

Warren found persisting low levels of radiation at ground zero and several kilometers away. While finding that the “intensity of radiation is quite low [it] is measurable with the very sensitive instruments used.” In some cases, the acceptable tolerance dose “is exceeded slightly.” Referring to the spread of fallout, he cited Japanese data “that patients in Nagasaki as far away as 4 kilometers [showed] effects of radiation.”

The MED’s 1946 public report made similar points, denying any health injuries from induced or residual radiation. “Black rain” was not yet on Warren’s mental map, although the phenomenon is mentioned in the Navy report.

Robert Serber, an early Manhattan Project recruit, joined Los Alamos Laboratory in 1943, where he played a significant role in weapons design projects. This report on flash burns was one of the results of his participation in the MED mission to Japan in the September 1945 [Serber appears in Figure 58 in Document 29B]. Serber reported on the effects of the radiated energy—“the total energy liberated … into radiant heat and light”—produced by an atomic explosion. The flash burn produced by the radiated energy was not a major cause of damage, but its impact was “very evident” and caused many casualties, which were described in the Final Report [See Document 26].

Serber’s report reviewed other flash burn effects, including the charring of telephone poles and the yellowing of foliage that had been green. Serber was able to deduce the height of burst from the angle of shadows cast by window frames and preserved on the walls of a room on the fourth floor of the Hiroshima post office building. “This turned out to be 1880’ plus/minus 50’, the probable error being estimated from the agreement between measurements made on different shadows.” According to Serber, 1850 feet was the expected altitude for the detonation, but later estimates indicated that it was 1898 plus or minus 50 feet.

Serber found it difficult to reach “any definite conclusion on the efficacy of the flash in setting fires, either directly, or, conceivably, through the spreading of burning debris by the blast.” The problem was that Japanese houses included various “fire making agencies, such as stoves,” which the blast effects would have overturned. “At both Nagasaki and Hiroshima the radius of nearly complete demolition of Japanese housing by blast was larger than the radius of complete coverage by fire.”

To develop legislation governing the use of atomic energy in the United States, the U.S. Senate created a Special Committee that held a series of public hearings in late 1945 and early 1946. In his testimony on 28 November 1945, Gen. Groves discussed the scope of the Manhattan Project, the problem of international control, and the destructive effects of atomic explosions. He did not provide a factual account of radiation effects, however, although the information provided by Stafford Warren would have made reasonably informative answers entirely possible. Perhaps wanting to preserve secrecy or possibly unwilling to admit uncertainty, Groves made bizarre and misleading statements to the senators.

When Senator Warren Austin (R-VT) asked Groves if there was any radioactive “residue” at Hiroshima or Nagasaki, Groves ignored Warren’s report with a definitive answer: “there is none. That is a very positive ‘none.’” While the senators did not believe there was anything morally wrong about the radioactive effects, Sen. Richard Russell (D-GA) observed that there was “tremendous fear” in the United States of atomic energy and its use, which made him want to know more. On radioactivity and the bombings generally, Groves said that he saw no choice between inflicting radioactivity on a “few Japanese” and saving “10 times as many American lives.” He claimed that no one suffered radiation injury “excepting at the time that the bomb actually went off, and that is an instantaneous damage.”

Groves continued to go out on a limb by declaring that it “really would take an accident for … the average person, within the range of the bomb to be killed by radioactive effects.” Going further out on a limb, Groves stated that the victims of radiation whose exposure was not enough to kill them instantly would die “without undue suffering. In fact, they say it is a very pleasant way to die.” Groves’ testimony has received scathing criticism as an “outrageous untruth” (Peter Wyden) and “patently untrue” (Eileen Welsome).[35]

Groves briefly quoted several passages from Johannes Siemes’ account, noting that the Jesuits had been among the “most accurate reporters of world events.” The final excerpt covered the philosophical debates between Siemes and his colleagues as to whether the atomic bomb was “in the same category as poison gas” – not to be used against civilians – or whether “total war in its present form is justifiable even when it serves a just purpose. Does it not have material and spiritual evil as its consequences which far exceed whatever good might result?”

While the Washington Post and the New York Times published accounts of the hearings, neither discussed Groves’ unusual testimony on radiation effects. By contrast, the Washington Evening Star provided a more detailed account of Groves’ testimony, although the reporter trustingly repeated and minimized the radiation claims: “Army inspections have shown convincingly, [Groves] said, that no one will be killed by radiation left after the bomb exploded, although such radiation may have been fatal to a few at the moment of the explosion.”[36]

In striking contrast to Groves’ testimony was the statement of Los Alamos physicist Philip Morrison, who had been with the U.S. group surveying weapons damage in Hiroshima and Nagasaki during September-October 1945. He gave the Senate Special Committee a thorough and affecting presentation of the damage inflicted by the initial blast, thermal effects, radiation and fire. In contrast to Groves, who said radiation sickness was “a very pleasant way to die,” Morrison described how those who survived the blast and heat “died anyway … from a further effect, the effects of radiumlike rays emitted in great number from the bomb at the instant of the explosion.” Highly impressed by the testimony, one of the Committee members, Senator Edwin Johnson (D-Co) said that “I should like to say to the witness, to Mr. Morrison, that he is the most eloquent witness that I have ever heard since I have been around Congress.” That would be far from the last public praise for Morrison, who became a well-known and respected advocate for the cause of nuclear disarmament.

The U.S. Navy sent an intelligence group – a “technical mission” – to do a wide-ranging investigation of a variety of topics, mainly involving naval technology but also the impact of the atomic bombings. Coordinated by Captain Clifton G. Grimes, Fleet Intelligence Officer in Charge of Intelligence for the Joint Intelligence Center, Pacific Oceans Area (JIC-POA), the technical mission to Japan had a staff of nearly 300 (including Japanese-Americans) who prepared dozens and dozens of reports based on captured documents and field work involving interviews/interrogations. The medical team, led by Naval Reserve Captain Shields Warren, a Harvard pathologist, produced two reports on the atomic bombings, including this report, which contains the striking finding: “The atomic bomb is the most terrible agent of destruction known to man.”[37]

Illustrated with culturally insensitive graphs, the Navy report provided broad coverage of radiation exposure, including “secondary” or “residual radiation” and their effects. The report provided detailed information on the fallout problem, with a finding of “physiologically significant” levels of “residual radiation” in outlying areas after the bombings, including potentially dangerous levels in Nagasaki’s Nishiyama district. One of the data points was a reference [see page 45] to what became known in Japan as “black rain” – radioactive “droplets of yellow-brown liquid” that fell after the explosion.[38]

The official guidance given to the MED, Army, and Navy teams was to investigate but not to participate in treatment because that could have been seen as an admission of “moral responsibility.” In practice, however, the situation was complex: doctors for all three groups gave advice to their Japanese colleagues, sometimes provided medical supplies, and gave their evaluation of specific cases, which had implications for treatment regimens. This pattern continued during the work of the Atomic Bomb Casualty Commission.[39]

Like Stafford Warren, Shields Warren found the Siemes narrative compelling and presented it in its entirety. The report included first-hand accounts by various Japanese who had been in Hiroshima and Nagasaki at the time of the bombings. In addition, the report had the benefit of collaboration with Japanese university-based researchers, who provided maps and other information, such as estimates of blast pressure. The report also drew on interviews with scientists for a brief estimate of Japanese wartime nuclear physics research. One of them, Professor Masao Tsuzuki with Tokyo Imperial University (now University of Tokyo), had used rabbits in radiation effects research in the 1920s. Tsuzuki worked closely with members of the U.S. survey teams, but as has been noted, he could be caustic. When Philip Morrison, with Los Alamos’ Weapons Physics Division, met Tsuzuki in Tokyo, the latter slapped him on the knee, saying, to the effect: “the Americans—they are wonderful. It has remained for them to conduct the human experiment.”[40]

A leading member of the British mission to the Manhattan Project, physicist and mathematician William Penney, conducted research that helped establish the optimum height of burst for the detonations above Hiroshima and Nagasaki to maximize their destructiveness. As a member of the team of scientists and medical doctors who traveled to the two cities during September-October 1945, Penney collected evidence on the physical destruction cause by the bombs, which he analyzed in this report.

Through visual inspection of flagpoles, shrines, cans, glass panels, wooden floors, and other things damaged in the blasts, and noting the distance of each from ground zero, Penney estimated the peak pressure, in pounds per square inch (p.s.i.), experienced by various objects and structures. Summarizing his results on pages 59-60, Penney estimated a peak pressure of 100 p.s.i. in Nagasaki based on damage to an earthenware drainpipe found 1200 feet from ground zero. For Hiroshima, Penney estimated a peak pressure of 35 p.s.i. at ground zero based on damage to the door of a safe. Penney’s report was probably the first systematic look at the problem of peak pressure, which would be a subject of continuing interest for war planners and civil defense specialists.

Penney’s summary of his major conclusions tacitly credited the calculations of Los Alamos scientists: Not only did “the bombs [perform] exactly according to design in their height of burst,” they were “placed in such positions that they could not have done more damage by any alternative bursting point.” Thus, the “extent of the blast damage was exactly that predicted.” In other words, the point of aerial detonation was to maximize damage, not to reduce radioactive fallout, as some later claimed.[41]

Penney explained that his report could guide any future use of atomic weapons: “the information collected would enable reasonably accurate predictions to be made of the blast damage likely to be caused in any city where an atomic explosion was conceivable.”

On destruction by fire, Penney observed that it was “tremendous” in both cities, but he did not attach any “special significance” to it, because he believed that it was a “property more of the cities themselves than of the bomb.” Writing that the explosions did not start any fires “instantly,” Penney said that “straw and many grass mats which were hanging outside to air, were ignited immediately and no doubt some fires were started in this way.” A “more likely cause” of fires, in his view, were “charcoal braziers, one of which was to be found in nearly every house.” He further added that the Japanese observed “many peculiar effects due to ‘fire winds’” that were not accurately recorded.

Commenting on radioactivity in a brief section about the “morale” effect of the bombings, Penney observed that the “danger of radioactive contamination on the ground terrified the whole population and had resulted in only spasmodic attempts at clearing debris.”

Among Penney’s “Main Results” were his estimates of the explosive yields for the Hiroshima and Nagasaki detonations. Penney estimated 5 kilotons (kt) of T.N.T. for Hiroshima and 20 kt for Nagasaki. The latter estimate would turn out to be roughly accurate, but 5 kt for Hiroshima was quite low. Years later, Penney and British colleagues produced an estimate of 12 kt for Hiroshima. In 1946, when Penney prepared this report, other Los Alamos scientists and officials were trying to establish yield estimates, but this was difficult for lack of precise data, such as the Enola Gay’s “true altitude” when it dropped the weapon.[42] During the 1980s, Los Alamos published estimates of 15 kt for Hiroshima and 21 kt for Nagasaki, acknowledging that “the outside limits of uncertainties in these values are believed to be 20 percent for Hiroshima and 10 percent for Nagasaki.

According to the British Mission, the purpose of its report “was less to list the damage which it found in Japan than to draw lessons from what was found which would be applicable to European targets and in particular, to Civil Defense in Great Britain.” With that underlying premise, the Mission declared that 50,000 was “the most important figure which this report contains”: it was the “standardized kill rate” of one atomic bomb.

The Mission arrived at the 50,000 number after reviewing the destruction caused by the atomic explosions, beginning with the blast and fire effects and then the “New Effects” of radiation and burns. Fire caused by explosive blast but also by heat effects was “the cause of much of the destruction.” Following a detailed account of structural and other damage caused by the blast (p. 53), the authors provided estimates of the explosive yields that were “somewhat academic and of doubtful value.” For Hiroshima, they estimated some 2600 tons of TNT; for Nagasaki, some 3270 tons. Those numbers were, as suspected, way off base because the explosive yields were in the range of 15,000 and 21,000 tons, respectively.

The Mission’s review of “New Effects,” included flash burns, heat and fire effects, and radioactivity. The “primary and secondary fires must be regarded as active dangers from atomic bombs.” The radiated heat produced high temperatures that “create conditions exceptionally favourable to the emergence and continuance of serious fires, however [they were] caused.” The discussion of radioactive effects and their health impacts downplayed “induced” (or residual) radiation as a cause of casualties but saw greater danger “for days or longer” from “primary fission products” caused by detonations on the ground or at lower altitudes.

At the beginning of the discussion of killed and wounded was a general statement that pointed to the complex causes of fatalities: Near the explosion’s center, a “high proportion of casualties, probably the bulk (except insofar as these were killed as it were several times over, by each casualty producing agent separately) died from secondary injuries.” The latter were either “mechanical injuries,” for example, “people being struck by falling buildings” (caused by blast effects), or burns. Concerning the latter, “it is probable that many people were burned because the fires started simultaneously in many places while they were trapped under or hemmed in by debris.” On injuries caused by over-pressure, the Mission was skeptical, noting reports of only a handful of ruptured ear drums respectively in Hiroshima or Nagasaki.

The review of fatalities in Hiroshima found that a range between 70,000 and 90,000 was more likely, but “probably not more than 120,000. For Nagasaki, 40,000 killed was the number “widely accepted by medical authorities,” but the Mission’s “preferred estimate” was 34,000 based on its calculations from “samples of known pre- and post-raid population and population movements.”

Drawing on the casualty estimates, the Mission found that “the standardized kill rate of one atomic bomb, air burst as in Japan and of similar size, exceeded 50,000.” That kill rate is “the expected number of killed in an area in which the density of population is uniform and 44 per acre—roughly the average density in central London.” According to the Mission’s report, “it is clear that the most serious danger presented by the atomic bomb is in producing casualties,” with the problem of “protection against gamma ray casualties in particular [being] exceptionally grave and difficult.”

Sometime during 1946, the British government published the substance of the Mission’s report, with photos.[43] The publication was a bowdlerized version, for example, by excluding the discussion of a “standardized kill rate” for atomic weapons. No doubt, British officials believed that information was too sensitive for public disclosure.

Following the interim report prepared by Stafford Warren was a final report, distributed in April 1946. Henry Barnett [Shown in Figure 58 in Document 28A], a pediatrician who went to medical school with Nolan and Hempelmann, played a key role in preparing this report along with Joseph Howland, an Army doctor at Oak Ridge who was later involved in human radiation experiments. Richard A. Tybout, a Corps of Engineers officer, prepared the chapter on radiation effects. The report has been declassified for decades, at least since fiscal year 1979, and is included here to show what U.S. government officials were learning at that time about radiation effects.

To protect the “health and morale of occupation troops,” the final report sought to “observe the total effects of the atomic bombs on the cities and the people exposed,” with the “specific objectives” of investigating “any unique effects due to radiation.” The Manhattan Project’s leaders saw that as important; first, because the Japanese were reporting the “appearance of uncanny delayed effects in persons exposed to the bombs which seemed unquestionably to be due to radiation.” Second, the Japanese were also “stating that people going into the cities after the bombings were developing similar symptoms.” For the well-being of U.S. occupation forces, it became “imperative” to determine whether those reports were valid. “This was the primary purpose of the entire mission.” That deeper knowledge of the “total effects” of atomic weapons on targeted areas and populations would provide useful data for future war planning was left unsaid but perhaps implied.

The report began with a summary of the damage and destruction and continued with casualty estimates and medical findings on injuries and radiation effects. The 200-page detailed medical study included chapters on pathology and the impact of gamma radiation with disturbing photographs of victims. None of this evidence upholds Groves’ glib statement about a “pleasant way to die.” Also included in the report are several accounts by U.S. and Japanese doctors on injuries caused by the explosions. One of them, by Dr. Masoa Shiotsuki, was on the scene at Omura Naval Hospital at Nagasaki when patients began to arrive. The medical study includes the text of the original preliminary report at PDF pages 163-178.

For fatalities, the final report estimated 78,000 in Hiroshima and 35,000 in Nagasaki, with an additional 37,000 and 30,000 injured, respectively. As the Interim Report noted, however, “The total number of causalities with the percentage of deaths and the distribution of the causalities and death, particularly in relation to the effects of radiation, can only be roughly estimated at the present time and may never be accurately known.”

As for the exact cause of fatalities, they could also only be guessed, and, “as was so aptly stated in the British Report, those near the center were probably ‘killed as it were several times over, by each casualty producing agent separately.’” According to the Final Report, “the proper order of importance for possible causes of [immediate] death … is burns [including flash burns], mechanical injury [“falling debris”], and blast.” As for deaths from radiation injury, information concerning hospital patients in both cities indicated a mortality rate of around 16 percent, although subsequent studies would show higher percentages.

On residual radioactivity, the report found “a small quantity of induced radioactivity … [but] it had not been sufficient to cause any demonstrable harm to persons living in the two cities after the bombings.” From the standpoint of the U.S. Army, that was a crucial point because of the initial concern that U.S. occupying forces could possibly be at risk of radiation exposure. There was more to say about residual radiation, however, because Navy medics raised telling questions about it in subsequent studies [See below].

Accompanying this report were two massive photographic studies on blast and fire damage to the cities. [See Documents 27A-C and 28 A-B]

Varley’s three-volume report includes photographs and captions prefaced by an overview of the physical damage and destruction caused by blast effects and fires, including estimates of the height of burst, William Penney’s estimates of peak blast pressures, the causes of fire spread, “unusual effects,” and casualty-producing effects. For total fatalities, Varley suggested a number far higher than the estimate in the main “Final Report,” “probably between the official figure of 92,000 and 126,000 reported by the Vice-Director of the Red Cross Hospital at Hiroshima.”

On fire damage, Varley reported that the atomic detonation caused “an immediate widespread incendiary effect.” The radiant heat was of “high intensity” but was not long enough to produce “sustained combustion of wood construction except in isolated cases.” According to Varley, “the uncontrolled fires that swept the city were mainly of secondary origin,” caused by the rapid collapse of frame buildings with many small and rapidly spreading fires produced by “overturned charcoal braziers, gas leaks, and possibly from electrical short-circuits.”

The PDF published here draws on the two copies of the report held by the National Archives, one in Record Group 77 of the Textual Records Division and the other in the Still Pictures Division. Photos are missing from both but the latter is more complete, with captions and photos in their proper order for the most part. Yet a few photos that appear in the version held by Textual Records do not appear in the Still Pictures copy, so several from the former have been interpolated in the version published herein, including a photo of the Commercial Museum showing the direction of the blast effects that struck the building, the “View Near ‘Zero Point,’” and the “Destruction Near Zero Point.”

A large, color-coded map showing the extent and severity of the devastation can only be found folded up in the copy of Volume I of the report held by the Still Pictures Division. Volume I also includes a chart with a “profile” of the peak pressure from the detonation based on a line that begins with the zero point and includes such buildings as the electrical company, the library, and city hall.

See description of Document 27A

See description of Document 27A

Note: The photos in these two volumes are slightly warped from sitting in an archival box for decades. They do not make optimum reproductions when using an overhead scanner such as ScanSnap.

The massive two-volume report on Nagasaki prepared by Maj. Walter C. Youngs [depicted in Volume I, figure 59] provided detailed analysis of the types of damage caused by blast and fire to buildings and other structures. On the fires, Youngs noted the impact of radiant heat and the blast’s secondary effects, concluding that the “overall damage from fire was practically as great as that caused by the blast concussion.” Youngs found that the percentage of casualties was very closely related to the distance from zero point and to the type of protection afforded,” for example whether people were out in the open or inside large buildings. “Casualties were heavier in wooden and masonry buildings, which were collapsed by the blast, than in the stronger structural steel and reinforced concrete buildings.” For numbers of fatalities in Nagasaki, the report provided a range of 35,000 to 40,000 as the “best” estimate.

Volume I of the Nagasaki report includes three folded up “Profile” charts, with their directions beginning from the zero point on the map. Drawing on numbers computed by William Penney, the profiles delineated peak pressures in pounds per square inch over densely built up areas, fields, and woods, including some specific structures (medical school, hospital, and a public school.

Volume I of the report includes discussion of a map showing the extent of devastation within concentric circles from zero point. The map itself has disappeared from the copy of Volume I, but a folded-up copy is in a supplementary volume in the same archival box, “Structural Damage in Nagasaki, Book I,” also prepared by Maj. Youngs. The rendering is more careful than the Hiroshima numbers computed by William Penney. The profiles delineated peak pressures in pounds per square inch over densely built-up areas, fields, and woods, including some specific structures (medical school, hospital, and a public school.

The captions for figures 31 and 32 in this volume, of “Japanese natives,” have an odd flavor of late 19th-early 20th century anthropology. Figure 31 probably depicts two recently discharged veterans while the caption for figure 32 indicates that it is of the “typical war-time dress of natives,” not recognizing that the Japanese dressed in various traditional and modern styles of clothing whether in war or peace. Thus, in contrast to the older kimono-clad older woman in figure 32, the young woman was wearing a jumper or pinafore, a type of dress that had been popular in the West for decades.

Like the copy of Varney’s Hiroshima report, many photographs are missing from the copy of the Nagasaki report. Unfortunately, there is no backup copy at the Still Pictures Division. There are additional compendiums of Nagasaki photographs in the same RG 77 collection, but they are too large to scan.

See description of Document 28A

Prepared by Shields Warren, this is a study in the histology, or microscopic anatomy, of atomic bombing victims based on data from autopsies conducted by Japanese and U.S. medical specialists. Written for the use of specialists, the report provides detailed coverage of the impact of ionizing radiation on the body’s organs. Slightly more accessible are the conclusions, which include a chronological presentation of the “pattern of injuries” from the moment of detonation through the weeks that followed, as more and more sickened or died from radiation exposure.

Part II of the report discussed residual radioactivity at Nagasaki on the basis of the research of Japanese scientists with Kyushu Imperial University (now Kyushu University) and the Institute of Physical and Chemical Research in Tokyo. Their data, evaluated by Warren as “essentially sound,” was the basis of diagrams at the close of the report, including the “detailed location of the explosion center” and the “pattern of deposition of fission products.”

This highly technical report on residual radioactivity by the Naval Medical Research Institute at Bethesda complemented the work of the Naval Medical Mission on the same topic. It found that the “deposition of fission products” (not yet called fallout) from the atomic bombings produced residual radiation in areas around Hiroshima and Nagasaki. The other source of residual radioactivity was “the production of radioactive isotopes in the ground materials by the extremely intense neutron and gamma ray production incident to the explosion.”

Two areas of Hiroshima and Nagasaki received close scrutiny. One was the village of Takasu, downwind from Hiroshima. There, the “residual activity in the Hiroshima area as a whole was far below physiologically significant intensity.” In the Nishiyama area of Nagasaki, however, the report found that “the maximal tolerance dose of radiation was exceeded for a sufficient length of time … to produce significant physiological effects but that it fell below the maximal tolerance dose fairly quickly.” Further research by Japanese experts with Kyushu Imperial University found “significant, although slight physiological effects” that were “capable of producing a measurable physiological change.”