You know how this works
In 1945, with WWII nearing its end, the walls closed in on the Japanese. The pressure was on and General Ishii feared what would follow the defeat of the Japanese Army.
Ishii ordered the cleansing of evidence that could incriminate Unit 731 and himself, including the human evidence.
Some 600 Chinese and Manchurian laborers working at the Pingfan facility were shot, the remaining 300 prisoners were gassed or poisoned, and facilities were destroyed.
The Pingfan facility proved to be a little too resilient. Parts of the Pingfan research complex were built with heavy concrete and withstood simple dynamite demolition attempts. So, workers loaded 80 trucks with 50,000 pounds of explosives and crashed them into the complex walls.
That attempt failed as well and parts of the Pingfan facility still stand to this day. Like this rat breeding cage…
With as much evidence destroyed as possible, Unit 731 researchers fled. General Ishii swore his scientists to silence and ordered them to disappear.
Run, but You Can’t hide
Many managed to escape the grip of Allied forces, but some did not and fell into the hands of microbiologist Lieutenant Colonel Murray Sanders, the officer chosen to investigate Japanese biological warfare on behalf of the United States.
LTC Sanders began his investigation with General Ishii's research assistant, Dr. Naito Ryoichi. While Ryoichi initially resisted interrogation, he didn't last long. LTC Sanders soon discovered that Dr. Ryoichi feared prosecution, especially prosecution by the communists.
Sanders leveraged this fear by threatening to offer Ryoichi up to the Soviets for interrogation and eventual prosecution. Ryoichi gave in and wrote a manuscript detailing some of Unit 731's exploits and a unit hierarchy map. However, Ryoichi did not disclose any human testing.
Sanders doubted Ryoichi's denial of human experimentation. Despite those doubts, he forwarded the information disclosed by Ryoichi to General McArthur, the Supreme Allied Commander.
Plot Twists of History
It's when the information of Unit 731 reaches McArthur that history starts to get confusing.
Instead of encouraging further investigation and prosecution of Unit 731 as you might expect, McArthur, with directions from Washington D.C., moved forward with a policy of immunity from war crime prosecution and public disclosure for Unit 731 and its members.
The policy was based on the idea that the “value to the U.S. of Japanese BW data is of such importance to national security as to far outweigh the value accruing from ‘war crimes’ prosecution.”
From that point forward, the United States was extremely protective of Japanese biological warfare data.
In 1947, the Soviet Union submitted a formal request to interrogate members of Unit 731. Following his orders from Washington, McArthur granted the request but dictated strict terms under which the interrogation could take place.
These terms included a requirement that all information gained must remain secret from all other countries and that American investigators be present during interrogations.
The U.S. even went so far as briefing up Ishii and other members of Unit 731 prior to their meetings with the Soviets. They were instructed not to divulge any important information to the Soviets and to not mention the discussions they'd previously had with the U.S.
Basically, Washington wanted complete control over Unit 731’s data.
The Cover-Up
The International Prosecution Section possibly had the heaviest hand in ensuring Unit 731 immunity. Frank S. Travenner Jr., Acting Chief of Counsel, not only dismissed Soviet claims of Unit 731 war crimes but actually threw out eye-witness testimony Soviets gained during their interrogations that could have implicated high-up Japanese officials in the crimes.
Travenner wrote to Soviet associate prosecutor Major-General A. N. Vasiliev that:
No evidence was brought to light which would indicate that these experiments were being made at the direction of the General Staff in Tokyo or that any reports have been received relating to these experiments. Chance of success…so slight that it is not considered wise or reasonable to request the U.S.S.R. to produce the witnesses under the circumstances.
Like McArthur, Travenner took his cues from Washington. In a letter from the Army Deputy Chief of Staff in reference to Unit 731, Travenner was told:
no action be taken on prosecution or any form of publicity
And that:
This is by direct order of the C-in-C [Commander-in-Chief] and CS [Chief of Staff]. Such publicity must be avoided in interests of defense and security of the US.
Travenner took this mandate seriously. A colleague of his, Colonel Thomas H. Morrow, produced evidence of chemical and bacteriological warfare which Travenner and the International Prosecution Section swiftly deemed insufficient for even raising the issue at court.
Morrow was then reassigned to a post in Washington.
Day in Court
The Military Tribunal of the Far East convened in 1946. Of the Unit 731 members who did stand trial, only those who had ties to the Pearl Harbor attack or the invasion of China were charged and sentenced.
Two additional reports were published before the end of the tribunal, the Fell Report, and the Hill and Victor Report. Both of these reports published evidence of human experimentation. The Hill and Victor Report concluded that:
Evidence gathered in this investigation has greatly supplemented and amplified previous aspects of this field. It represents data which have been obtained by Japanese scientists at the expenditure of many millions of dollars and years of work. Information had accrued with respect to human susceptibility to those diseases as indicated by specific infectious doses of bacteria. Such information could not be obtained in our laboratories because of scruples attached to human experimentation.
Despite evidence showing Unit 731 committed the worst medical atrocities in human history, life went on for Ishii and his men. Tamura Yoshio, a Pingfan alumnus, recalled that most people who were members of Unit 731 “simply pretended not to know anything about what they had done”.
General Shiro Ishii, the man who started this all, was never prosecuted and was allowed to live out the rest of his life in peace. He died of throat cancer in 1959.
U.S. Applications
As more information on Unit 731 comes to light, the question of what the U.S. did with the data remains mostly unanswered.
We do know, however, the U.S. military dropped plague bombs during the Korean war. Chinese footage of the war shows U.S. shells releasing insects into the open. Tests conducted by an independent research group on those insects returned positive for Bubonic plague.
At least one U.S. pilot is documented as having admitted to carrying such munitions. These accounts hint at why Washington found it prudent to cover up crimes against humanity.
If we include the lives lost to U.S applications of Unit 731 technology, the toll is likely to ring much higher than half a million logs.
Sources
https://web.archive.org/web/20190731012542/https://www.umflint.edu/sites/default/files/groups/Research_and_Sponsored_Programs/MOM/b.altheide.pdf
https://www.archives.gov/files/iwg/japanese-war-crimes/select-documents.pdf
https://www.nytimes.com/1995/03/17/world/unmasking-horror-a-special-report-japan-confronting-gruesome-war-atrocity.html?pagewanted=all