The files were released on Monday by the National Security Archive, a private research organization based at George Washington University in Washington, DC.
The findings show US Army Gen. Leslie Groves, who oversaw the Manhattan Project, lied to Congress and the American public about the harmful effects of radiation exposure. They also reveal J. Robert Oppenheimer, the director of the Los Alamos lab at the center of the project and the subject of a recently released major motion film, knew about Groves’ deception and did nothing to correct it.
At first, Groves claimed the radioactive materials were harmless out of simple ignorance, but later it became deliberate deception, the files show.
The day prior, Groves told reporters that radiation had caused no deaths, dismissing reports in Asian newspapers as “propaganda.” While the Imperial Japanese government had announced its surrender on August 15, the war was not formally concluded until the peace treaty was signed on September 2.
Later reports from November of that year described further cases of radiation sickness among Japanese victims. One report by the Manhattan Project’s chief medical officer, Stafford Warren, dated November 27 described thousands of cases in Japanese hospitals that were consistent with the effects of radiation poisoning, which US scientists had already closely documented up-close after several of their own suffered catastrophic irradiation and died while developing the atom bomb.
The report was addressed to Groves, who three days later, told the Senate Special Committee on Atomic Energy when asked about “radioactive residue” in Hiroshima and Nagasaki: “There is none. That is a very positive ‘none.’”
Groves acknowledged many had died from radiation exposure, but claimed it was from the time the bomb went off and not from fallout. In a shutter-inducing moment of the testimony, he claimed radiation victims would die “without undue suffering. In fact, they say it is a very pleasant way to die.”
Other documents show that while the atom bomb was still in development, the scientists already feared a toxic “cloud” of “radioactive dust” could be stirred up by the weapon’s explosion and loiter in the air for “hours after the detonation.” They urged Groves to evacuate the test site prior to the Trinity blast that July, but Groves dismissed their fears, accusing them of being “a Hearst propagandist” - that is, a writer for a notorious muckraking newspaper.
Five days after the Trinity test, on July 21, 1945, Warren wrote in a document included in the dossier that “the dust outfall from the various portions of the cloud was potentially a very serious hazard over a band almost 30 miles wide extending almost 90 miles northeast of the site,” adding that there was still “a tremendous amount of radioactive dust floating in the air.”
However, nine days later, Groves told US Army Chief of Staff Gen. George Marshall that “no damaging effects are anticipated on the ground from radioactive materials” by using the weapon.