When Unit 731’s hidden compound in northeastern China was finally destroyed in August 1945, the colossal incinerators that had burned for nearly a decade were used one last time—not just to dispose of mutilated human remains, but to erase every trace of the horrors committed inside. With Hiroshima and Nagasaki flattened by atomic bombs and the Red Army closing in, orders arrived from a surrendering Tokyo demanding that all incriminating evidence be destroyed. Research facilities were gutted. Thousands of documents detailing vivisection, torture, weapons testing, and rape went up in flames.
Hundreds of kilograms of dried anthrax were destroyed, and evidence of biological attacks against Chinese cities turned to ash. All potential witnesses were killed. The 300 remaining prisoners were given a choice between suicide by cyanide or by hanging, while 600 forced laborers were summarily executed. There has not been a single documented survivor.
The Japanese personnel who still worked at the unit were told to disappear. Potassium cyanide vials were pressed into their hands. Just before they fled, Unit 731 blew up its own headquarters. The destruction, however, was largely in vain.
When the Tokyo War Crimes Trial began on May 3, 1946, the man most responsible for the atrocities—General Shirō Ishii, the ruthless director of Unit 731—was absent from the list of defendants. The victorious American occupiers did not want justice; they wanted the data. Millions of dollars flowed from Washington into the hands of anonymous former unit members in exchange for complete immunity. Most of those responsible for the biological and chemical warfare facility would never face justice, and many went on to forge comfortable, often celebrated careers in the medical industry.
The extent of Unit 731’s atrocities was only declassified decades later, and Japanese government officials continue to deny involvement to this day. —
To understand how such horrors were possible, one must look at Japan’s imperial ambitions in the early 1930s. In 1932, a song called the “Manchuria March” was among the most played in Japan, celebrating the bravery of soldiers killed in the Russo-Japanese War and in the recent conquest of Manchuria. The new puppet regime propped up there appeared to Japanese imperialists as a utopian dream.
Manchuria—a region as large as Britain and France combined—offered huge economic and industrial potential. It also provided a powerful outpost to watch over the nearby, recently colonized Korea. Japan’s Kwantung Army had seized the northern Chinese province in 1931 after the false flag Mukden Incident precipitated the full invasion. A modest Japanese presence had existed since the Treaty of Portsmouth in 1905, which ended the Russo-Japanese War and granted Japan permission to lease the southern branch of the China Far East Railway.
But Japan argued it should be allowed to exercise total authority within the South Manchuria Railway Zone, eventually stationing soldiers there under the facade of protecting the railway. Further south, the Republic of China’s nationalist government was looking to reassert control over a country weakened by warlordism. In 1929, troops under Manchurian warlord Zhang Xueliang had been defeated by the Soviet Red Army in a conflict over the Chinese Eastern Railway. The weakness of the Chinese military only emboldened the Japanese.
At 10 p. m. on September 18, 1931, a bomb laid by a Japanese lieutenant near a section of railway was detonated, killing no one. A train passed by the site without difficulty less than half an hour later.
Still, the Kwantung Army blamed Chinese nationalists—a perfect *casus belli* for a full-scale invasion. In response, Japanese troops attacked a nearby Chinese garrison. Within months, 40,000 Japanese soldiers had poured into the region. The new puppet state, dubbed Manchukuo, was born.
To feign legitimacy, Puyi—the last emperor of China, toppled after the fall of the Qing dynasty—was installed as its nominal leader. To much of the world, the policies seemed relatively legitimate. A journalist for *The Sun* in Sydney wrote that while the efficiency of Japan’s coup indicated careful organization, it must not be inferred that Japan was necessarily the aggressor. The journalist blamed anti-Japanese persecution and Soviet-inspired nationalism for provoking the invasion.
During the Tokyo War Crimes Trial more than a decade later, however, former prime ministers testified that the government in Tokyo had no control over the Kwantung Army’s decisions in Manchuria. The testimonies painted a picture of a small military clique completely beyond civilian control. Despite private doubts that seizing Manchuria would isolate Japan internationally, Emperor Hirohito published an imperial rescript praising the army for acting in “self-defense” against Chinese bandits. —
As the Kwantung Army established its foothold, proposals for a Japanese biological and chemical weapons program were just beginning.
At the head of this venture was Lieutenant General Shirō Ishii. Born on June 25, 1892, in the Japanese village of Chōta, a two-hour drive from central Tokyo, Ishii grew up in one of the wealthiest families in the area. Their vast land holdings gave the family an air of aristocracy. As the fourth son of patriarch Katsuya Ishii, his opportunities seemed limitless.
He attended Shiba Middle School, then the Fourth Higher School in Kanazawa, and by 1916 enrolled at Kyoto Imperial University’s faculty of medicine, graduating in 1920 and marrying the university president’s daughter. In his book on Unit 731 testimonies, historian Hal Gold regarded Ishii as “a problem for others—pushy, inconsiderate, and selfish. ” He spent a year as a commissioned military surgeon in the Imperial Army before returning for postgraduate medicine at Kyoto, where he disturbed classmates by completing lab work in the middle of the night and keeping pet bacteria in Petri dishes around the classroom. Over the next decade, Ishii was at the forefront of campaigns to establish Japan’s own biological weapons program.
He had taken a two-year tour of the West, conducting extensive research into the effects and possibilities of biological and chemical warfare. Wars of gas and bacteria were also far more affordable than conventional warfare. While germ warfare had been brutally exploited by colonial governments to subdue indigenous populations in the Americas and Australia since the 18th century, it was only in response to Germany’s use of biological weapons during World War I that the 1925 Geneva Protocol explicitly banned the use of germs in international armed conflicts. The prohibition only inspired Ishii.
He soon followed the Japanese Army into Manchuria, initiating the first phase of Japan’s biological weapons program in a precursor to the infamous Unit 731. —
While the biological weapons facility was given a fairly legitimate mandate by Imperial Japan, it was well understood that its operation should be kept at an obvious distance from Tokyo. Manchuria offered two major incentives: safe separation from the government and an abundance of test subjects. Harbin was the first stop for Ishii and his few hundred army men when they arrived in 1932.
But it quickly became clear that conducting such operations in the bustling metropolis would be too visible. Boarding the now firmly Japanese South Manchuria Railway, Ishii and his men went south. In an impoverished neighborhood with about 300 homes and shops, the vast fields in the south were what attracted Ishii and his men. Everyone living in the village was forced out in three days.
Houses were torched, and Ishii moved in. A restricted military zone was established over a 500-square-meter plot, and highly surveilled Chinese laborers were recruited to help with construction. Brick buildings went up, and an airport was built. The final design contained two main sections: one for living quarters, offices, and dining areas; the other for the organization’s very core—laboratories, prisons, munitions factories, and, importantly, a colossal crematorium.
This first compound became known as the Zhongma Fortress. Twenty-four-hour security guards were stationed at the double iron doors. The facility was bound by three-meter-high walls covered in barbed and electric wire. Even trains passing by were made to keep their shades drawn.
According to Hal Gold, the life expectancy of inmates held in the fortress was said to be just one month after arrival. Early tests sought to determine how long a person could last on water alone, how much blood could be drawn from prisoners, and how inmates fared after injections of plague bacteria. If a prisoner survived an experiment but was too weak for further tests, they were killed instantly. The facility wouldn’t last long.
In August 1936, after a heavy downpour deactivated the compound’s searchlights and electric fence, one prisoner planned an escape. During the autumn harvest festivals, an inmate named Lee grabbed a guard’s hands and hit him on the head. Lee took the keys from the guard’s waist, unlocked nearby cells, and with dozens of other prisoners ran through the compound, forming a human ladder against the final wall. Lee insisted on forming the base of the ladder.
As others climbed out, one final shout was heard from Lee before a barrage of bullets crashed against the wall. While most escapees were either gunned down or recaptured, a few men reached a nearby village. Five years after the facility had been established, the secret of the Zhongma Fortress was out—and so were Ishii’s men. —
The publicity from the escape testimony was enough to cause a clandestine relocation to a much larger site in Pingfang, a region much closer to Harbin.
Unit 731 was one of several units established as covert branches of the Epidemic Prevention Research Laboratory at the Japanese Army Military Medical School in Tokyo, dedicated to the development of biological warfare. A year after his promotion to second-class senior Army surgeon in 1935, an undeterred Ishii was given the keys to the official Unit 731. Soon his career ascent triggered even a personal transformation. A former member of the unit recalled that on first meeting, Ishii was “slovenly dressed, his uniform covered with food stains and ashes from numerous cigarettes.
” But when the two met again in Manchuria, Ishii was “dressed immaculately, his uniform was spotless, and his sword was tied correctly. ”
Especially after Japan’s invasion of China in 1937, the number of biological and chemical warfare units increased rapidly. At the operation’s peak, about 20,000 personnel were employed across the units. Unit 731 had by far the largest backing in Pingfang.
As with the Zhongma Fortress, hundreds of villages were expelled. Ishii’s men—now including civilians—took over a sprawling walled city made up of more than 70 buildings, likely finished around 1939. This time, no one would lay eyes on the unit. Even aircraft entering the airspace above the compound would be shot down.
The prison cells were built side by side. Each room contained a flushable toilet, wooden flooring, and thick concrete walls. A hole was built near the floor through which prisoners would extend an arm to receive injections or have blood drawn. Cells were kept clean and prisoners relatively well fed to keep test results standardized.
Three massive incinerators were built and quickly put to use. One former employee recalled: “The bodies always burned up fast because all the organs were gone. The bodies were empty. ”
Screams could be heard from every corner of the complex—the hum of low-pressure chambers, the relentless rattle of shackles, the whirl of human-sized centrifuges, and the constant crackle rising from the furnaces.
Hundreds of guards sat in complete emotional detachment as Unit 731 charged ahead. Chinese and Korean citizens were the unit’s most common victims, but exiled Russians in the region were also regularly captured by military police and brought back for testing. —
The atrocities that took place inside Unit 731 over its near-decade of operations were horrific, and the experiments only grew in morbidity. Prisoners were infected with plague, dysentery, cholera, and typhus.
Bacteria would be injected, and once the first stages of infection could be examined, prisoners were taken to the dissection room. One former unit member described a victim “stripped and placed on the table screaming, trying to fight back,” strapped down and still screaming frightfully. A doctor stuffed a towel into his mouth, then with one quick slice of the scalpel, opened him up. Vivisection became second nature to the medical men running the unit.
Plague-infected wheat flour was poured onto nearby villages from the air. Village dogs were captured, fed cholera-laced pork, and sent back. The Chinese cities of Ningbo, Changde, and Nanjing were the worst hit, with tens of thousands of people killed in the subsequent epidemics. At production peak, the Japanese manufactured 300 kilograms of plague, 500 kilograms of anthrax, 800 kilograms of typhoid, and 1,000 kilograms of cholera each month.
Forty-five kilograms of plague-carrying fleas were incubated per production cycle. There were reports of dozens of victims who lost hands and feet as a result of frostbite testing. Even babies born to prisoners were subjected to subfreezing temperatures. These tests directly informed accepted practices still used to deal with frostbite today.
According to Hal Gold, some frostbite tests resulted in “the flesh and muscle falling from the bones. ” Other experiments left bones so brittle they shattered from blows by clubs. Either way, the eventual result was the same: gangrene and the rotting away of extremities. While some tests were conducted in the freezing Manchurian outdoor temperatures, others took place inside a refrigerated lab that could reach temperatures as low as −70°C.
Testimony from a nurse attached to the unit’s maternity section revealed that women were forcibly impregnated and injected with syphilis so transmission to newborns could be studied. Soon, however, the study of venereal disease by injection was abandoned. Instead, researchers started forcing prisoners into sexual acts with each other—a male and female, one infected with syphilis, brought together in a cell and forced into sex. Anyone resisting would be shot.
Other former unit members claimed Chinese prisoners were shot in the stomach at point-blank range so surgeons could attempt to remove the bullets before the victim died. Beheaded captives had their organs instantly cut out to check how long they could function afterwards—their hearts were often still beating. Dozens of prisoners were herded into concrete dugouts and gassed. When one victim miraculously survived, air was injected straight into his veins.
Captives were burned to death, spun to death, and hung upside down until death. The experiments were limitless in their cruelty. While estimates vary, thousands of prisoners were murdered within the walls of Unit 731, and hundreds of thousands of people were killed by the epidemics that Ishii’s men created. —
Once Tokyo realized Soviet entry into Manchuria was imminent, Unit 731’s facilities had to be destroyed.
At 6 p. m. on August 14, 1945, orders arrived insisting the unit be blown up. Cells were stripped bare, and just 30 unit members were left to kill the remaining prisoners and detonate the compound.
A specially authorized train carried the fleeing medical men from Pingfang through the Korean Peninsula and finally across to Japan by sea. Ishii instructed his subordinates to take the secret of Unit 731 to their graves. While the Red Army captured 12 of the unit’s researchers and tried them in December 1949, they got off reasonably lightly in exchange for information gathered over the preceding decade. Those captured by the US were secretly given immunity for the same exchange of data, which was then used by both countries in their own bioweapons programs.
Despite negotiating immunity with US authorities, Shirō Ishii spent his last years terrified of Soviet indictment. His cold, hostile demeanor and propensity for cruelty—once vital to his sky-high success—were unwelcome in the reformed professional world of post-war occupied Japan. The ruthless medical master behind Unit 731 contracted throat cancer and died in relative obscurity in 1959 at age 69. Other higher-ups in the unit went on to enjoy respected careers in the post-war order.
Some received awards for scientific discovery. Others spent years in prestigious research labs. More became executives at top universities. Unlike in the Soviet trials, Unit 731 was actively left out of the Allies’ war crimes trials.
American historian Gary J. Bass called the failure to prosecute those involved in Japan’s biowarfare program “one of the gravest stains of the Tokyo trial. ”
The horrors of Unit 731 remain one of the most under-examined chapters of World War II—a story of unspeakable cruelty, institutional denial, and justice never fully served.