Unit 731 was a covert biological and chemical warfare research and development unit of the Imperial Japanese Army that undertook lethal human experimentation during the Second Sino-Japanese War (1937–1945) and World War II. It was responsible for some of the most notorious war crimes carried out by Japanese personnel. Unit 731 was based at the Pingfang district of Harbin, the largest city in the Japanese puppet state of Manchukuo (now Northeast China).
It was officially known as the Epidemic Prevention and Water Purification Department of the Kwantung Army. Originally set up under the Kempeitai military police of the Empire of Japan, Unit 731 was taken over and commanded until the end of the war by General Shiro Ishii, an officer in the Kwantung Army. The facility itself was built between 1934 and 1939 and officially adopted the name “Unit 731” in 1941.
Ishii’s first facility was in the city of Harbin; however, the need for secrecy made it necessary for Ishii to relocate his group to a prison camp 60 miles away. After this camp was blown up by escapees, an installation called Ping Fan was constructed about 14 miles from Harbin. When completed in 1940, what became known as Unit 731 housed some 3,000 personnel. At a ceremony honoring the event, the now General Ishii made the facility’s purpose crystal clear. A doctor’s “god-given mission,” Ishii said, was to block and treat disease, but the work “upon which we are now about to embark is the complete opposite of these principles.” In the name of defeating Japan’s enemies, Ishii and his staff spent the next five years mixing witch’s brews of pathogens that cause some of the world’s most horrific diseases: anthrax, plague, gas gangrene, smallpox, and botulism, among others. They then used Chinese prisoners (dismissively termed maruta, or “logs”) as guinea pigs, forcing them to breathe, eat, and receive injections of deadly pathogens. Allied POWs were also allegedly targeted.
Between 3,000 and 12,000 men, women, and children—from which around 600 every year were provided by the Kempeitai—died during the human experimentation conducted by Unit 731 at the camp based in Pingfang alone, which does not include victims from other medical experimentation sites. Almost 70% of the victims who died in the Pingfang camp were Chinese, including both civilian and military. Close to 30% of the victims were Russian. Some others were South East Asians and Pacific Islanders, at the time colonies of the Empire of Japan, and a small number of Allied prisoners of war. The unit received generous support from the Japanese government up to the end of the war in 1945.
Ishii and other members of the Togo unit would draw 500 cc of blood from selected prisoners every few days. Once they had grown too weak to be of further use, they were “sacrificed” by lethal injection. Prior to disposal in the Zhong Ma crematorium, it was usual for the cadaver to be dissected. Ishii’s first crude attempts on biological weapons focused on three contagious diseases: anthrax, glanders and plague. Plague infected fleas lured from mice were used to produce a bacterium that was injected in to prisoners. Within ten to twelve days the infected “logs” were writhing with temperatures of 40 degrees Celsius. One prisoner survived in these conditions for nineteen days. All were eventually dissected while alive.
In another experiment two “bandits” were subjected to Phosgene gas, injected in to a brick-lined room. Another was injected with 15 mg of Potassium cyanide. Others burned under 20,000 volts of electricity. Not a fatal dose, they were later disposed of by poison injections. Still others were slowly roasted to death by lower but continuos voltages. All experiments were subject to meticulous record keeping.
The Unit was also keenly interested in “frostbite” experimentation. This was a particularly important project. Frostbite degraded military efficiency during the bitter Manchurian winters. By the time Ishii’s research facility was relocated to the massive Ping Fan complex in 1939, frostbite tests were routine. Echoing similar work by the notorious Nazi, Dr. Josep Mengele, naked prisoners – males and females – were subjected to sub-freezing temperatures. Later they were “defrosted” by a range of experimental techniques. It was usual for these “logs” to have their limbs beaten with sticks until they resounded with a hard, hollow ring – signifying the freezing process was complete.
All of these atrocities had been banned by the Geneva Convention, which Japan signed but did not ratify. By a bitter irony, the Japanese were the first nation to use radiation against a wartime enemy. Years before Hiroshima, Ishii had prisoners’ livers exposed to X-rays.
His work at Pingfan was applauded. Emperor Hirohito may not have known about Unit 731, but his family did. Hirohito’s younger brother toured the Unit, and noted in his memoirs that he saw films showing mass poison gas experiments on Chinese prisoners.
Japan’s prime minister Hideki Tojo, who was executed for war crimes in 1948, personally presented an award to Ishii for his contribution in developing biological weapons. Vast quantities of anthrax and bubonic plague bacteria were stored at Unit 731. Ishii manufactured plague bombs which could spread fatal diseases far and wide. Thousands of white rats were bred as plague carriers, and fleas introduced to feed on them.
Plague fleas were then encased in bombs, with which Japanese troops launched biological attacks on reservoirs, wells and agricultural areas.
Infected clothing and food supplies were also dropped. Villages and whole towns were afflicted with cholera, anthrax and the plague, which between them killed over the years an estimated 400,000 Chinese.
In 1922 Ishii had returned to Kyoto Imperial University to further his education and knowledge of bacteriology, serology, preventive medicine, and pathology. That same year he was sent to Kyushu. There, a highly contagious disease had become extremely aggressive and claiming many lives. The disease caused a severe amount of swelling to the brain and was extremely difficult to study. Ishii approached the problem from a different direction, rather than studying the disease (he was unable to do so efficiently because the problem lay in the brain where he was unable to get to before the patients died) he studied how to prevent effective water filtration so that soldiers weren’t drinking liquid parasites. He did this well, and because of it received much acclaim from his colleagues, and it is said that he even demonstrated how his product worked in front of the Emperor of Japan himself (supposedly Ishii swore by his filtration so much that he urinated in the filter and then proceeded to drink the clean water the filter produced). In April of 1928 Ishii left Japan to travel the world for two years studying. Ishii visited clinics and laboratories in almost thirty countries. He went everywhere from Russia to America, Germany and France. He returned with information he believed would drastically alter the fate of Japan.
Many of the human experiments were intended to develop new vaccines or treatments for medical problems the Japanese army faced. Many experiments remain secret, but an 18-page report prepared in 1945–and kept by a senior Japanese military officer until now–includes a summary of the unit’s research. The report was prepared in English for U.S. intelligence officials and it shows the extraordinary range of the unit’s work.
There are scores of categories that describe research about which nothing is known. It is unclear what the prisoners had to endure for entries like “studies of burn scar” and “study of bullets lodged in the brains.”
Scholars say that the research was not contrived by mad scientists and that it was intelligently designed and’ carried out. The medical findings saved many Japanese lives.
For example, Unit 731 proved that the best treatment for frostbite was not rubbing the Limb, which had been the traditional method but immersion in water a bit warmer than 100 degrees, but never mom than 122 degrees.
The cost of this scientific breakthrough was borne by those seized for medical experiments. They were taken outside and left with exposed arms, periodically drenched with water, until a guard decided that frostbite had set in. Testimony From a Japanese officer said this was determined after the “frozen arms, when struck with a short stick, emitted a sound resembling that which a board gives when it is struck.”
In 1944, when Japan was nearing defeat, Tokyo’s military planners seized on a remarkable way to hit back at the American heartland: they launched huge balloons that rode the prevailing winds to the continental United States. Although the American Government censored re. ports at the time, some 200 balloons landed in Western states, and bombs carried by the balloons killed a woman in Montana and six people in Oregon.
Half a century later, there is evidence that it could have been far worse; some Japanese generals proposed loading the balloons with weapons of biological warfare, to create epidemics of plague or anthrax In the United States. Other army units wanted to send cattleplague virus to wipe out the American livestock industry or grain smut to wipe out the crops.
Monument for Unit 731 in TokyoThere was a fierce debate in Tokyo, and a document discovered recently suggests that at a crucial meeting in late July 1944 it was Hideki Tojo – whom the United States later hanged for war crimes – who rejected the proposal to use germ warfare against the United States.
Partly because the Americans helped cover up the biological warfare program in exchange for its data, Gen. Shiro Ishii, the head of Unit 731, was allowed to live peacefully until his death from throat cancer in 1959. Those around him in Unit 731 saw their careers flourish in the postwar period, rising to positions that included Governor of Tokyo, president of the Japan Medical Association and head of the Japan Olympic Committee.