Unit 731 Site (Pingfang, Harbin)

Unit 731 (731部隊, Nana-san-ichi Butai), formally designated as the Epidemic Prevention and Water Purification Department of the Kwantung Army (関東軍防疫給水部本部), was the Imperial Japanese Army's covert biological and chemical warfare research program. Its sprawling headquarters complex was constructed in the Pingfang District of Harbin, in the Japanese puppet state of Manchukuo (present-day Heilongjiang Province, China), approximately 24 kilometers south of the Harbin city center.

The unit was established in 1933 as a small research group under Army surgeon Shiro Ishii (石井四郎), who had studied biological warfare techniques abroad and convinced the military leadership of their strategic potential. In 1936 the program was formally expanded and incorporated into the Kwantung Army, and work began on a massive purpose-built facility at Pingfang. The compound encompassed over 150 buildings spread across 6 square kilometers, including laboratories, operating rooms, prison blocks, cremation furnaces, an airfield, barracks, a power station, and a railway siding. At its peak, the unit employed approximately 3,000 personnel, including some of Japan's most prominent medical researchers.

The facility's most notorious activities were its human experiments. Prisoners — predominantly Chinese civilians and soldiers, but also Koreans, Mongolians, Russians, and Allied POWs — were subjected to horrific procedures without anesthesia. Victims were deliberately infected with plague, cholera, typhoid, anthrax, and other pathogens to study disease progression. Vivisections were performed on living subjects to observe the effects of disease on internal organs. Other experiments involved frostbite exposure, hypobaric pressure chambers, blood transfusion between incompatible blood types, and weapons testing on live targets. Prisoners were dehumanizingly referred to as "maruta" (丸太, meaning "logs"), a reference to the facility's cover story as a lumber mill. At least 3,000 people are generally accepted to have been killed within the facility, with some estimates running to 10,000 or more, while the field use of biological weapons across China — including the deliberate contamination of water supplies and aerial dispersal of plague-infected fleas — is estimated to have killed a further 200,000 people or more.

As Soviet forces advanced into Manchuria in August 1945, Unit 731 personnel attempted to destroy the facility and all evidence of their activities. Buildings were dynamited, documents were burned, and remaining prisoners were killed. Despite these efforts, the physical remains of the complex survived in part. After the war, the United States granted immunity to Unit 731's leadership — including Ishii himself — in exchange for exclusive access to their biological warfare research data, a decision that effectively suppressed public knowledge of the program for decades.

Today, the site is preserved as the Museum of Evidence of War Crimes by Japanese Army Unit 731 (侵華日軍第七三一部隊罪証陳列館). Originally opened in 1985, the museum underwent a major expansion in 2015, with a new 9,997-square-meter exhibition hall divided into six thematic zones covering the history of Japanese biological warfare, the structure of Unit 731, human experimentation, weapons development, field deployment, and postwar evidence and trials. Several original buildings remain on site, including the headquarters building and boiler room chimney. The museum is designated as a National Key Cultural Relics Protection Site by the Chinese government and receives hundreds of thousands of visitors annually. It stands as one of the most important memorial sites documenting Japanese wartime atrocities and the history of biological warfare.