U.S. forces ordered all mail items sent to ex-Unit 731 members to be censored
U.S. forces instructed the General Headquarters of the Allied Forces to censor mail items sent to 21 people linked to Japan's notorious Unit 731 that conducted research on germ warfare during World War II, it has emerged.
Taketoshi Yamamoto, professor of media history at Waseda University, has found a relevant document from among U.S. official documents preserved at the National Diet Library.
"The censorship occurred before the Tokyo Tribunal of War Criminals. It may have been necessary for granting Unit 731 members immunity from prosecution," said Yamamoto.
After Japan's defeat in the war, U.S. forces granted Unit 731 members immunity from prosecution as war criminals in return for providing data on the unit's human testing and other experiments. However, it had not been known that U.S. forces were monitoring the moves of former Unit 731 members and others linked to the unit by censoring mail items sent to them.
The document, dated Feb. 15, 1946, was sent from the U.S. Army to the Civil Censorship Department (CCD) of the Allied Forces' General Headquarters. It was treated as a secret document.
It instructed the CCD to censor mail items sent to 12 people including Shiro Ishii, head of Unit 731; Ryoichi Naito, an aide to Ishii and the founder of pharmaceutical firm Green Cross; and Kanji Ishihara, former lieutenant general with the defunct Imperial Japanese Army who played a key role in the Manchurian Incident.
The document states that the CCD should closely examine any reference to Ishii and germ warfare and meetings between those involved.
The document also lists nine other people with a medical background, who had allegedly worked at the unit's research facility. U.S. forces required the CCD to pay close attention to their moves.
The lists of 21 people include figures that have not been known as those linked to Unit 731.
U.S. forces began to question those linked to the unit in September 1945, shortly after they occupied Japan. They attempted to draw detailed information on the unit's activities by hinting at granting them immunity from prosecution as war criminals.
In 1947, U.S. forces decided not to prosecute members of Unit 731 in return for providing data on their experiments.