Six of the most disturbing “experiments” were carried out by Unit 731, the Imperial Japanese Army’s gruesome biological and chemical warfare research unit.

For hundreds of millions of people, World War II was a living nightmare. It’s as if all the world’s developed countries had a surplus of rage and hatred that they had been storing up, and it all erupted during the war years.

None of the areas in which World War II was fought lasted as long as what became known as the Pacific Theater. In fact, Japan may have started the war by attacking Manchuria in 1931, and it may have ended the war by invading China in 1937.

The disturbances and upheavals caused by these invasions shook China to its core, triggering a civil war and famine that killed more people than lived in Canada and Australia combined, and lasted until the country’s “liberation” by the Soviets in 1945.

And, of all the atrocities committed by Imperial Japan against the Chinese people during this brutal occupation — and there were some stunning crimes committed, even by World War II standards — the operations of Unit 731, the Japanese biological warfare unit that somehow plumbed new depths in what was already a nearly genocidal war, were probably the most heinous.

Despite its innocent beginnings as a research and public health agency, Unit 731 evolved into a production line for weaponized diseases that, if fully deployed, could have killed everyone on Earth several times over. All of this “progress” was, of course, built on the never-ending agony of human prisoners, who were used as test subjects and walking disease incubators until Unit 731 was disbanded at the end of the war.

In the violent past of Unit 731, these six programs stand out among a long list of atrocities:

Frostbite Testing

Yoshimura Hisato, a physiologist assigned to Unit 731, was intrigued by hypothermia. Hisato routinely submerged prisoners’ limbs in a tub of ice-filled water and held them there until the arm or leg had frozen solid and a coat of ice had formed over the skin as part of Maruta’s study on limb injuries. When struck with a cane, the limbs made a sound similar to a plank of wood, according to one eyewitness.

Frost bite testing unit 731

Hisato then experimented with various methods for rapidly rewarming the frozen appendage. He did this by dousing the limb in hot water, holding it near an open fire, and leaving the subject untreated overnight to see how long it took for the person’s own blood to thaw it out.


Unit 731 began as a research unit, looking into the effects of disease and injury on an armed force’s fighting ability. One component of the unit, dubbed “Maruta,” went beyond the usual bounds of medical ethics by observing injuries and disease progression in living patients.

Vivisection unit 731

Initially, these patients were army volunteers, but as the experiments reached the limits of what could be observed non-invasively, and as the supply of volunteers dried up, the unit turned to the study of Chinese POWs and civilian prisoners.

And as the concept of consent vanished, so did the researchers’ restraint. Unit 731 began referring to confined research subjects as “logs,” or “Maruta” in Japanese, around this time.

These experiments’ research methods were barbaric.

For example, vivisection is the practice of mutilating human bodies without anesthesia in order to study the operations of living systems. Thousands of men and women, mostly Chinese communist prisoners, as well as children and elderly farmers, were infected with diseases such as cholera and the plague, and their organs were removed for examination before they died, allowing researchers to study the effects of the disease without the decomposition that occurs after death.

Subjects’ limbs were amputated and reattached to the opposite side of the body, while others had their limbs crushed or frozen, or their circulation was cut off, to track the progression of gangrene.

Finally, once a prisoner’s body had been consumed, they were usually shot or killed by lethal injection, though some may have been buried alive. None of the Chinese, Mongolian, Korean, or Russian detainees assigned to Unit 731 survived.

Weapons test

The Japanese Army was deeply interested in the impact of various weapons. Unit 731 herded prisoners onto a firing range and blasted them from varying distances with a variety of Japanese weapons, including the Nambu 8 mm pistol, bolt-action rifles, machine guns, and grenades. The wound patterns and penetration depths on the bodies of the dead and dying inmates were then compared.

weapon testing

Bayonets, swords, and knives were also tested in this manner, though the prisoners were usually bound during these tests. Flamethrowers were also put through their paces on both covered and exposed skin. Furthermore, gas chambers were installed at unit facilities, and test subjects were exposed to nerve gas and blister agents.

Heavy objects were dropped on bound prisoners to study crush injuries, subjects were locked up and deprived of food and water to see how long humans could survive without them, and victims were given injections of mismatched human or animal blood to study transfusions and the clotting process.

Meanwhile, long-term X-ray exposure sterilized and killed thousands of research participants, as well as caused horrific burns when the emitting plates were miscalculated or held too close to the subjects’ nipples, genitals, or faces.

Unit 731 personnel loaded human beings into large centrifuges and spun them at higher and higher speeds until they lost consciousness and/or died, which usually happened around 10 to 15 G’s, though young children showed a lower tolerance for acceleration forces.

Syphilis Experiments

Since the venereal disease has been the bane of organized militaries since Ancient Egypt, it stands to reason that the Japanese military would be interested in syphilis symptoms and treatment.

Syphilis Experiment unit 731

To learn what they needed to know, doctors assigned to Unit 731 infected prisoners with the disease and withheld treatment to observe the illness’s uninterrupted progression. However, a modern treatment, a primitive chemotherapy agent called Salvarsan, was sometimes given over a period of months to observe the side effects.

To ensure effective disease transmission, syphilitic male prisoners were ordered to rape both female and male fellow inmates, who would then be monitored to see if the disease developed. If the first exposure did not result in infection, more rapes would be arranged until it did. 

Rape And Forced Pregnancy

Rape became a regular feature of Unit 731’s experiments, in addition to syphilis.

Female prisoners of childbearing age, for example, were sometimes forcibly impregnated in order to subject them to weapon and trauma experiments.

The pregnant subjects were opened up and the effects on the fetuses were studied after they were infected with various diseases, exposed to chemical weapons, or suffered crush injuries, bullet wounds, or shrapnel injuries.

The plan appears to have been to translate the teams’ findings into civilian medicine, but if Unit 731’s researchers ever published their findings, the papers did not survive the war.

Germ Warfare

The entire foundation of Unit 731’s research was in support of their larger mission, which by 1939 was to develop horrifying weapons of mass destruction for use against the Chinese population, as well as presumably American and Soviet forces if the time came.

Germ Warfare unit 731

To that end, Unit 731 went through tens of thousands of prisoners at various facilities throughout Manchuria that had been occupied by imperial forces for years. Inmates at these facilities were infected with several of the most lethal pathogens known to science, including Yersinia pestis, which causes bubonic and pneumonic plague, and typhus, which the Japanese hoped would spread from person to person after deployment and depopulate disputed areas.

Doctors monitored patients for rapid onset of symptoms and rapid progression in order to breed the most lethal strains possible. Prisoners who survived were shot, but those who became ill the fastest were bled to death on a mortuary table, and their blood was used to infect other prisoners, the sickest of whom were bled to pass on the most virulent strain to a new generation.

One member of Unit 731 recalled that very sick and unresisting prisoners were laid out on the slab so that a line could be inserted into their carotid artery. When the majority of the blood had been extracted and the heart was no longer able to pump, an officer in leather boots climbed onto the table and jumped on the victim’s chest with enough force to crush the ribcage, causing another dollop of blood to spurt into the container.

When the plague bacillus was thought to be of sufficient lethality, the last generation of infected prisoners were exposed to massive numbers of fleas, Y. pestis’ preferred vector of contagion. After that, the fleas were packed in dust and sealed inside clay bomb casings.
On October 4, 1940, Japanese bombers dropped these casings over the Chinese village of Quzhou, each containing 30,000 fleas that had sucked blood from a dying prisoner. Witnesses to the raid described fine reddish dust settling on surfaces throughout town, followed by a rash of painful flea bites that afflicted nearly everyone.

According to contemporary accounts, more than 2,000 civilians died of plague as a result of this attack, and another 1,000 or so died in nearby Yiwu after the plague was carried there by sick railway workers. Other anthrax attacks in the area killed approximately 6,000 more people.

After Hiroshima and Nagasaki were bombed, the Soviet Army invaded Manchuria and annihilated the Japanese Army, and the Emperor read his infamous surrender declaration over the radio, Unit 731 was officially disbanded in August 1945.

Its records were mostly burned, erasing any useful information the team had accumulated over the course of 13 years of research. Researchers mostly reintegrated into civilian life in occupied Japan as if nothing had happened, with many of them rising to positions of prominence on university faculties.

Japan has never apologized for, and China has never forgiven, the countless atrocities committed by Japanese forces against China between 1931 and 1945. As the last witnesses to this history grow old and die, it’s possible that the issue will be forgotten.

Leave a comment

Your email address will not be published. Required fields are marked *