The horrifying crimes and brutal experiments of the secretive WWII Japanese ‘Unit 731’

After Japan seized control of Manchuria in 1931, military leaders identified the region as a practical location for developing new military technologies.

General Shirō Ishii, a microbiologist with military rank, proposed the establishment of a dedicated facility to explore the potential of biological warfare.

He convinced superiors that scientific weapons could offer Japan a strategic advantage in future conflicts. 

In 1936, Japanese authorities approved the creation of a military unit disguised as a public health organisation.

Its formal title was the “Epidemic Prevention and Water Purification Department of the Kwantung Army” but it gave no hint of its true purpose.

Behind this cover, Unit 731 operated with the intention to build deadly tools for use in war. 

At a site just outside the city of Harbin in northern China, construction began on a large site known as the Pingfang facility.

The location allowed the Japanese to work away from outside interference, while access to prisoners from the occupied population made sure a steady supply of human test subjects.

The site included research laboratories, administrative buildings, barracks, prison cells, and crematoria.

At its height, more than 3,000 staff worked there. 

Under the direct support of the Japanese high command, Unit 731 grew into a highly organised and well-funded project.

Its secrecy ensured that information rarely leaked beyond a tight circle of insiders. 

General Shirō Ishii was the founding architect of the program, as he was trained in medicine and public health, and he combined it with a scientific drive and military loyalty.

His early experiments attracted attention in Tokyo, where he secured funding and support from senior figures in the Imperial Army.

Ishii built a network of specialists from Japan’s leading medical universities instead of working alone, and was promoted to major general in 1941. 

At the beginning of 1942, Ishii stepped back from day-to-day command, though he continued to influence decisions from behind the scenes.

His position was formally filled by Lieutenant General Masaji Kitano, another military physician with prior involvement in the program.

Kitano maintained the operational focus and preserved the systems that Ishii had created.

Under his supervision, experiments continued without interruption. In fact, after the war, Kitano became a senior figure in the Green Cross pharmaceutical company in Japan, which became mired in scandals decades later. 

Among the key figures were Colonel Tomosada Yoshio and Major General Kawashima Kiyoshi.

They oversaw sections of the facility and coordinated operations between laboratories, supply teams, and medical teams to ensure that the unit carried out its work efficiently and without moral restraint. 

During its operation, Unit 731 drew in hundreds of researchers, guards, and assistants.

Many had academic qualifications in biology, chemistry, and medicine. Some joined the unit for personal advancement, while others did so out of belief in Japan’s military goals.

However, few expressed concern about the methods used or the cost in human life. 

The main goal of Unit 731 focused on the development of biological weapons that could cripple enemy populations.

Japan’s war planners wanted tools that could cause mass death without relying on conventional arms.

Disease, they believed, offered an invisible and uncontrollable form of destruction that could be directed at cities, armies, or supply chains. 

To accomplish this, the unit’s scientists required accurate data on how pathogens behaved inside the human body.

Infected prisoners were kept under continuous watch while researchers tracked the spread of illness.

They examined blood, tissue, and internal organs over time, and they adjusted variables and conditions to improve their results.

The pathogens tested included plague, anthrax, cholera, typhoid, and glanders. 

At the same time, experiments tested how long people could survive without water, how much cold the human body could endure, and what injuries resulted from explosive blasts.

Subjects were burned, frozen, or injected with toxins, and researchers forced them to ingest chemical agents. E

xplosives and flamethrowers were also tested on prisoners tied to stakes. 

In addition to laboratory work, Unit 731 tested weapons in the field. Japanese aircraft dropped ceramic bombs filled with plague-infected fleas onto villages in 1940.

Water sources were laced with cholera or typhoid. There are also accounts of outbreaks in cities such as Changde in 1941, although some historians dispute whether the contamination there was deliberate or resulted from unrelated causes. 

Behind the walls of the Pingfang compound, surgeons cut open living prisoners to observe the effects of untreated infections.

Victims were restrained without anaesthetic and subjected to organ removals, blood transfusions, or exposure to pathogens. 

In some rooms, doctors amputated arms and legs, then stitched them to other parts of the body to study shock and rejection.

Once tissue began to rot, the results were recorded and analysed. Some captured Soviet soldiers may have been used in frostbite tests, although the extent remains uncertain. 

Elsewhere in the compound, women were raped and impregnated so researchers could monitor the transmission of disease during pregnancy.

Some were deliberately infected with syphilis and gonorrhoea, while children were included in tests, particularly twins, whose development under controlled conditions offered comparisons useful to the scientists. 

Far from the facility, villagers in selected areas were targeted during field tests.

Food and clothing were tainted with deadly bacteria. Also, flea bombs released insects carrying plague into populated regions.

Victims had no warning, no treatment, and no chance of survival. 

The overwhelming majority of victims were Chinese civilians, many arrested without cause and taken from their homes.

Soldiers, suspected rebels, and political prisoners were also included. Other victims came from Korea, Mongolia, and the Soviet Union.

There are no verified records confirming the use of Allied prisoners in the experiments, and claims to that effect remain speculative. 

Upon arrival at Pingfang, prisoners received a number instead of a name. They were referred to as “logs” or maruta, a term that reduced people to just objects.

The term also came from a cover story that described the facility as a lumber mill.

Their background, age, or health condition made no difference. Once inside, they were expected to die in the course of research. 

Prisoners were housed in cells, given minimal food, and denied access to medical care. Most were unaware of what awaited them.

Some believed they would be relocated or released. Instead, they were drawn into a system that used them up and discarded them in crematoria. 

Throughout the war, Japanese commanders ignored any appeals for humane treatment.

The facility operated in complete secrecy, and soldiers who worked there were sworn to silence.

Guards who spoke out were punished or reassigned. Most complied without resistance. 

After Japan’s surrender in 1945, American occupation forces uncovered fragments of evidence from Unit 731.

Investigators collected documents, examined the site, and questioned some of the surviving personnel.

Reports reached the highest levels of U.S. command, including General Douglas MacArthur. 

Rather than prosecute those involved, American officials offered immunity to key scientists in 1947 in exchange for their research.

The United States wanted access to data that could support its own biological weapons program.

Much of the material was sent to Fort Detrick, Maryland, the centre of America’s biological warfare research.

In pursuit of this goal, it classified the findings and refused to share them with Allied governments. 

Several scientists who had led Unit 731 returned to civilian life. Some held posts in major universities, medical centres, or pharmaceutical companies.

Shirō Ishii avoided prosecution and lived in relative comfort until his death in 1959. His name never appeared before any war crimes tribunal. 

In contrast, the Soviet Union held its own trial at Khabarovsk in December 1949. A handful of Japanese officers received prison sentences, though the event gained little attention outside Eastern Europe.

Testimony showed the use of plague bombs and deliberate contamination of water supplies, but Western governments dismissed the trial as propaganda. 

Throughout the post-war decades, victims’ families sought recognition. Court cases, petitions, and protests failed to force any official apology.

Textbooks in Japan excluded the story. Politicians refused to address it. Public knowledge stayed limited until the 1990s, when former soldiers and researchers began to speak. 

Today, Unit 731 is one of the most horrific examples of human experimentation in modern history.

The crimes committed, once hidden and dismissed, show how easily scientific research can become a tool of cruelty under the shield of war.

The former Pingfang compound has since been turned into the Unit 731 Museum.

While commemorative efforts began in the 1980s, the official museum opened in 1996 and expanded in later decades to educate new generations about these atrocities.