Established in 1935, Unit 731 was officially known as the Epidemic Prevention and Water Purification Department of the Kwantung Army. Under the Imperial Japanese government, the unit worked to develop biological and chemical weapons and performed cruel and frequently fatal tests on detainees throughout the Second Sino-Japanese War (1937–1945) and World War II. These experiments are thought to be among the most inhumane war crimes ever carried out.
Formation of Unit 731
Japan began pursuing an aggressive, expansionist, and imperialist foreign policy in the early 1930s. In September 1931, Japan invaded Manchuria in northeastern China, established control over the region, and created the Manchukuo puppet state. Sino-Japanese relations began to crumble, resulting in the outbreak of the Second Sino-Japanese War in 1937.
Despite the 1925 Geneva Protocol ban on the development of chemical and biological weapons (entered into force in 1928; Japan was one of the signatories of the protocol), the Japanese Imperial government envisioned that in order to achieve its foreign policy goals in Asia and establish itself as a dominant power, the Japanese Imperial Army required aggressive modernization and innovation.
Following this goal, Unit 731 was established in 1935 near the Pingfang district of the Manchurian capital, Harbin, under Japanese occupation. With the stated goal of promoting public health, it became known as the Kwantung Army’s Epidemic Prevention and Water Purification Department.
In reality, the department’s goals included finding out how the human body might resist various illnesses and starvation, as well as testing and researching the impacts of recently discovered biological weapons on the human body.
At its initial stage, Unit 731 gathered volunteers to participate in the experiments. However, as the war intensified and the experiments expanded, the Japanese Imperial Army ultimately approved the use of prisoners of war for these experiments. The majority of the victims were Russian and Chinese. A small portion of Koreans and Mongolians were also included in the experiments.
The ideological justification for establishing Unit 731 was based on the assumption that the Chinese and Koreans were racially inferior to the Japanese. Centuries of conflict and rivalry with China and Korea in order to acquire dominance in East Asia contributed to the rise of Japanese nationalism. The Meiji Restoration from 1868 and the subsequent rapid industrialization and modernization of Japan further cemented the perception that Japanese advancement was the result of its racial and cultural superiority.
Thus, in the mid-20th century, Japan actively pursued the aim of establishing itself as a dominant power. The need to develop biological warfare was based on racial superiority: By weakening and eliminating “racially inferior” people in the region, Japan sought territorial expansion and regional dominance.
The Leadership of Unit 731
Ishii Shiro, widely known as the “[Josef] Mengele of the East,” is considered the founding father of biological warfare in Japan.
Drawing inspiration from the 1925 Geneva Protocol, he deduced that biological warfare must be an effective instrument to uphold Japan’s dominance, given how much it was feared and opposed.
Ishii Shiro began his career as an army doctor, finished medical school at Kyoto Imperial University, and was appointed head of the biological warfare research program established by the Japanese government in 1931. Ishii was able to advocate for his ideas to the Imperial Army’s higher authorities by arguing that the conventional military forces were more costly to maintain, while lethal pathogens and chemical weapons were alternatively inexpensive to develop and utilize.
According to Ishii, biological warfare research could be categorized into two pillars: “assault research” and “defense research.” Initially, Ishii and his team of researchers focused on the development of “defense research,” which meant creating new vaccines to safeguard the Japanese army from infectious diseases during the war efforts.
To conduct “assault research,” Ishii saw the need to establish a research site outside of Japanese territory. In doing so, Ishii implied that his experiments would not be ethically justified to conduct on racially superior Japanese citizens but would “be acceptable with supposedly lower races.”
When Japan invaded Manchuria in China in 1931 and occupied the whole territory in 1932, Ishii acquired the site abroad he needed.
In 1936, Japanese Emperor Hirohito ordered the creation of a network of biological weapons research units all over Asia. Unit 731, built in the Ping Fang district of Harbin, Manchuria, became the headquarters. It had 3,000 personnel, 150 buildings, and the capacity to allocate 600 prisoners at a time for experimental use.
The Japanese government supplied Dr. Ishii with leading scientists and physicians. Those who refused to participate were labeled Hikokumin (traitors). However, working with Dr. Ishii was held in such high esteem that most medical professionals saw it as a noble service to their country.
Unit 731 received almost unlimited equipment and funds from the Japanese government and had affiliated locations in Nanking (Unit 1644), Beijing (Unit 1855), and Changchun (Unit 100). The total number of personnel involved reached 20,000.
Human Experimentation at Unit 731
The intense construction of the Unit 731 buildings in Manchuria caused an interest in the local population. When asked what the building was meant for, ironically, the answer was a “lumber mill, and the people are the logs.” From this point, “log,” or maruta in Japanese, was widely used in reference to prisoners of Unit 731.
In practice, the researchers at Unit 731 investigated the effects of various infections on the human body, such as syphilis. Researchers actively studied the symptoms, ways of onset of the disease, and its treatment. They forcibly infected male prisoners with the pathogens and observed the transmission process of these pathogens among female prisoners through coerced sexual interactions.
Special gas chambers were set up to investigate test subjects’ reactions and durability against blister gas and nerve gas. The effects of high G-forces and prolonged X-ray exposure on the human body were also examined.
One of Unit 731’s physiologists, Yoshimura Hisato, was particularly interested in hypothermia. Hisato’s inhumane experiments included submerging prisoners’ limbs in ice-cold water until they became frozen and a coat of ice formed over them. Hisato recorded the length of time it took for frostbites to appear on human bodies and used a variety of techniques to quickly thaw the frozen limbs (hot water, fire, or leaving the subject untreated).
At Unit 731, active vivisection—the practice of performing surgery on living organisms for research or experimental purposes—was carried out without the use of anesthesia. Prisoners were infected with deadly diseases (such as cholera and plague) and vivisected to study the effects of the diseases on human organs.
Unit 731 in Practice
The Japanese Imperial Army first utilized the results of the inhumane experiments at Unit 731 in October 1940 against the inhabitants of Kaiming Street in Ningbo, Zhejiang, China. Japanese planes dropped wheat, corn, and cotton infected with the bubonic plague in targeted areas. Just days following the attack, more than 100 people died of the disease.
Ningbo authorities erected a four-meter isolation wall around the area, but unable to contain the spread of the disease, Kaiming Street was eventually burned. The Ningbo region remained closed until the 1960s and is widely known as the “plague field.”
Another instance of attempted Japanese biological warfare is the siege of Bataan in the Philippines in March 1942. Japan intended to unleash 200 pounds, or almost 150 million insects, of fleas that spread the plague. However, the plan never came to reality. The battle was over by the time the assault was prepared.
The Battle of Iwo Jima, which took place against the United States in February and March 1945, was another botched biological siege. Two gliders carrying pathogens were to be towed over the battlefield and released, but the gliders did not reach their destination.
By 1945, Japan was struggling to advance against the Allied Powers of World War II. Operation PX, also known as Operation Cherry Blossoms at Night, was the Japanese plan for a biological attack on cities in southern California. The plan was scheduled to be executed on September 22, 1945. According to the operation, aircraft were to be launched from I-400-class submarines. They were ordered to drop “bombs” containing the plague-infested fleas. Operation PX failed due to the opposition of Army Chief of Staff General Yoshijiro Umezu.
The Legacy of Unit 731
Japan was defeated in World War II. As the Allied forces entered Japan, they began to investigate war crimes and atrocities committed by researchers at Unit 731. The information became available to the US intelligence agencies and military personnel through interrogation of the Japanese political and military officials involved in the establishment and functioning of Unit 731.
Lt. Col. Murray Sanders of the US Army recommended to US President Harry Truman and General Douglas MacArthur in 1945 that Unit 731 should be kept secret and used to further the United States’ scientific endeavors in the context of the Cold War. President Truman accepted. Thus, Dr. Ishi and his subordinates received immunity from prosecution as war criminals.
Both the experimental locations and the subsequent documents were destroyed. The primary explanation for how the United States and Japan managed to keep the history of Unit 731 secret during the Cold War was the fact that no victim who entered the facility survived.
Despite the inhumane nature of the experiments, medical researchers and leaders of the units continued to live without the legal consequences of their brutal actions. They kept working in medical facilities, institutions, and different industries. Dr. Shiro Ishii returned to private practice. He passed away in 1959 from throat cancer.
Up until the 1990s and the end of the Cold War, Japan’s biological and chemical weapons program was mainly kept in the shadows.
Regarding the matter, historian and Professor Emeritus of History at California State University, Sheldon Harris, in his authoritative history of the Japanese biological warfare program, argues:
“The questions of ethics and morality as they affected scientists in Japan and in the United States never once entered into a single discussion… In all the considerable documentation that has survived… not one individual is chronicled as having said [biological warfare] human experiments were an abomination and that their perpetrators should be prosecuted. The only concern voiced was that of the possibility of exposure that would cause the United States some embarrassment should word of the bargain ever become public knowledge.”
Only in the late 1990s did Japan acknowledge the existence of Unit 731 by disclosing testimonies from former members, photographs, and documentary evidence.
The history and legacy of Unit 731 are both violent and cruel, corresponding to sadistic indulgence in the name of science, without producing any meaningful results for Japan militarily or politically during World War II. Much like the acquired research results had no significant implications on the scientific advancements of the United States during the Cold War.
