Inside Unit 731, Japan's Gruesome WWII Human Experiment Program

By: John Donovan  | 
unit 731
A building on the site of the Harbin bioweapon facility of Unit 731 stands in ruins today. Japanese troops, including those in Unit 731, developed and produced germ weapons based on experiments on human beings and used the weapons against Chinese civilians. Wikimedia/(CC BY-SA 3.0)

Key Takeaways

  • Unit 731, a Japanese Imperial Army program, conducted deadly medical experiments and biological weapons testing on Chinese civilians during WWII.
  • Thousands of prisoners were killed in cruel experiments, and perhaps hundreds of thousands more died from biological weapons testing.
  • The true extent of Unit 731's actions was shielded from public knowledge for years, with the U.S. granting immunity to top officials in exchange for research.

For years after World War II, in most of what was considered the "civilized" world, the truth behind Japanese Imperial Army Unit 731 was quietly swept away. Facts were suppressed. Memories questioned. Reports denied.

Even today, the true extent of Unit 731's wartime actions — horrendous, deadly medical experiments and lethal biological weapons testing on unsuspecting Chinese civilians — is known largely only to historians and scholars.


But the facts are out there for those who seek them. And for those who seek to use them for their own personal reasons.

"I think that it has become a piece of this tortured dialogue over the war between Japan and China. The Chinese have seized upon this quite a bit. And the Japanese right, the nationalist right, their basic view is that, 'Oh, the Chinese. This is all political.' ... And there is a certain truth to that," says Daniel Sneider, a lecturer in international policy at Stanford's Freeman Spogli Institute for International Studies. "There is a 'uses of the past' question here. Perhaps you could say it's cynical in that everybody does it."

The truth is that Japan's Unit 731 committed some of the most heinous war crimes ever. Thousands of prisoners were killed in cruel human experiments at Unit 731, which was based near the northeastern China city of Harbin, north of the Korean peninsula and on a border with Russia. Perhaps hundreds of thousands more — maybe as many as a half-million — were killed when the Japanese tested their biological weapons on Chinese civilians.

The exact number of dead is not known. It may never be known.

"It's very difficult to calculate," says Yue-Him Tam, a history professor at Minnesota's Macalester College and co-author of a book entitled, "Unit 731: Laboratory of the Devil, Auschwitz of the East (Japanese Biological Warfare in China 1933-1945)." Tam, born and raised in China, has taught a class at Macalester on war crimes and memory in contemporary East Asia for more than 20 years. "If you include those victims who suffered from the other activities — not necessarily just used as human guinea pigs — the bombs in China ... it's very difficult to calculate."

unit 731
These ruins are all that's left of the Japanese germ factory run by Unit 731, a covert biological and chemical warfare research and development unit of the Imperial Japanese Army during World War II.
Xiaolu Chu/Getty Images


The Start of Unit 731

Unit 731 — its official name was the Epidemic Prevention and Water Purification Department of the Kwantung Army — was formed before World War II began (at least for the U.S., which didn't officially enter the war until December 1941). It came about sometime in the mid-1930s when Japan and China went to war, a conflict that eventually morphed into World War II's war in the Pacific theater.

The Unit's charge was clear from the beginning: testing, producing and storing biological weapons. Such activities were outlawed by at least two international treaties at the time, though the Japanese did not ratify the 1925 Geneva protocol. It didn't matter.


From the start, Unit 731, under General Shirō Ishii, was merciless.

Among the thousands of experiments conducted on prisoners: vivisections without anesthesia; injections of venereal diseases to examine their spread; amputations to study blood loss; removal of other body parts and organs; starvation; and deliberate exposure to freezing temperatures to examine the effects of frostbite. From a 1995 article in The New York Times, relating a story from a medical assistant in Unit 731:

The Chinese prisoner had been deliberately infected with the plague as part of a research project — the full horror of which is only now emerging — to develop plague bombs for use in World War II. After infecting him, the researchers decided to cut him open to see what the disease does to a man's inside. No anesthetic was used, [the former medical assistant] said, out of concern that it might have an effect on the results.

Reportedly, not one of the thousands of prisoners that were experimented on — most of whom were Chinese, though many were Russian or Korean — survived.

Later, the Japanese took especially virulent forms of the plague and other pathogens that were developed at Unit 731, put them in canisters and dropped them on nearby towns to see if their weapons would work. They did.

Thousands of these still-dangerous bombs remain in the Chinese countryside today, Tam says. Some people still suffer from the Japanese "dirty" bombs.

At one time, the Japanese hatched a plan to infect fleas with a plague manufactured at Unit 731 and drop flea-filled bombs, launched from planes stored aboard submarines, on San Diego in a mission code-named Operations Cherry Blossoms at Night. The war ended before the plan could be executed.

After the U.S. dropped atomic bombs on Japan and effectively ended the war in 1945, Japanese leaders ordered the destruction of Unit 731, which included more than 150 buildings and two airports. As the victorious Allied forces approached, many hundreds of remaining prisoners were killed. The thousands of people who worked in the place and conducted experiments on healthy, living humans scattered, many never to face justice.

unit 731
This photo shows the frostbitten hands of a Chinese prisoner at Unit 731 who was taken outside in winter by Japanese troops for an experiment on how best to treat frostbite.
Xinhua via Getty Images


America's Shameful Part

The top doctors and soldiers at Unit 731 kept careful records of their experiments, and used them to leverage their way to freedom after the war. When the Allies swept into China, they agreed to grant Ishii and many of his associates immunity from prosecution for war crimes. The reasons: The U.S. wanted Unit 731's research for its own use, and it wanted to keep that information out of the hands of others, including the Russians. Thus, for years, the true nature of what went on in Unit 731 was shielded from public knowledge.

Some of the truth came out in the Khabarovsk War Crimes Trial, held in that Russian city in December 1949. Twelve members of Unit 731 and associated units were tried. All were found guilty and imprisoned. Despite that trial, though, much of what went on in Harbin was immediately classified by the U.S. government and remained clouded in secrecy.


More details about Unit 731 are still being unearthed. A confession from a unit commander, written to U.S. interrogators at a base in Maryland shortly after the war, was released in August 2021 by a Chinese provincial agency. Chinese and Russian news outlets heralded the release, which highlighted America's part in using the information gathered by Unit 731, hiding it and protecting its sources from further prosecution.

"The United States is not the outsider to this. Previously, I think the tendency was for the people in the United States to think, 'This is a problem between Japan and its neighbors.' But not only were we of course the major combatant in the war, we shaped the postwar settlement, including decisions like the one concerning Unit 731," Sneider says. "We made the big decisions about what was a war crime and what wasn't ... We're the creator of the postwar order, and therefore we have responsibility and involvement in dealing with the issues that were left, unfortunately, unresolved."

unit 731
This exhibit at The Museum of Evidence of War Crimes by Japanese Army Unit 731 in Harbin, shows how the Japanese would freeze prisoner's hands and then pour hot water over them to test how they thawed.
Global Photos


Dealing With Unit 731 Today

Research on 731 continues to be conducted all over the world. As recently as 2018, the Japanese government provided a list of more than 3,600 members of Unit 731 to a Japanese scholar. Yet even with more information, with politicians and the governments of various countries opening their records, the facts remain largely in the shadows and in some dispute.

In China, with the resurgent government now not as dependent on Japan as it was in the years following World War II, the Chinese are demanding more answers, eager to hold old rival Japan responsible.


For their part, most Japanese are not nearly as willing to engage in discussions about what is considered by many Japanese as a shameful period in that country's history. Some say the surge in Chinese interest in Unit 731 is nothing more than political in nature.

The U.S. is dealing with its own internal demons about its history with Unit 731.

These varying viewpoints, and others in the region and throughout the world, complicate matters. From 2006 to 2016, Sneider and others at Stanford's Walter H. Shorenstein Asia-Pacific Research Center conducted a project, "Divided Memories and Reconciliation," aimed at examining the historical memory of the wartime period in Asia. These histories, viewed differently, go directly to ideas about national identity and nationalism. They are tricky histories to examine, uncovering differences that often stay unresolved.

"Sometimes the truth is pretty elusive," says Sneider. "To some degree, the goal is not necessarily always to establish 'the fact.' That's a good goal, but it may not be possible. The goal, if you're seeking reconciliation, the goal may be to understand the different perceptions of the other.

"In Japan, wartime memory is highly contested within Japan. They've been battling over these issues since 1945. Sometimes it's important just for Koreans and Chinese and Americans to understand what's going on within Japan. That path is contrived; to try to get to reconciliation by agreeing on what happened."

People may not agree on how many people were killed by the criminals in Unit 731, who did it, how it was done, or why it occurred. They can, and should, look critically upon America's decisions after the war, too.

But this much is indisputable: What happened in Unit 731 was an abomination.

In August 2015, The Museum of Evidence of War Crimes by Japanese Army Unit 731 opened in an area just south of Harbin, a city of more than 5 million people. Tam is among the millions who have visited the site.

"The room where they experimented with poisonous gas, there are still walls standing there, and the walls are really thick, almost like 1-meter [3.2-feet] thick, to prevent leaking of something. When I saw these things, I was really shedding tears as to how people can do that," Tam says. "It was very moving.

"I am a historian. The most important thing that matters to me is the facts. I want to find out the facts. And that was a fact, Unit 731. The crimes they committed and produced are facts."

General Shirō Ishii
General Shirō Ishii, seen on the left in wartime and on the right at a "reunion" for those who worked at Unit 731 after World War II, was never charged with war crimes.
Wikimedia/(CC BY-SA 3.0)


Frequently Asked Questions

How did Unit 731's activities impact international laws on human experimentation?
The atrocities committed by Unit 731 highlighted the need for stricter international laws, contributing to the development of the Nuremberg Code and other ethical guidelines for human experimentation.
What were the long-term health effects on survivors of Unit 731's experiments?
Survivors suffered severe physical and psychological trauma, including chronic illnesses, disfigurement and PTSD.