As the world approaches the 80th anniversary of the end of World War II, a fresh wave of revelations has thrust Japan’s notorious wartime germ warfare program back into the spotlight. The release of long-sealed military documents in 2025 has galvanized researchers, reigniting public debate and stirring painful memories in both Japan and China. The story of Unit 731 and its network of secret biowarfare detachments is once again making headlines, not just for the horrors of the past, but for the uncomfortable truths about justice, accountability, and the politics of memory.
In August 2024, 95-year-old Hideo Shimizu, one of the last living eyewitnesses to Unit 731’s atrocities, returned to China after nearly eight decades. According to Xinhua, Shimizu visited the Exhibition Hall of Evidences of Crime Committed by Unit 731 in Harbin, northeast China. There, he publicly acknowledged the crimes of the Japanese Imperial Army and offered apologies to the victims. The gesture was extraordinary, as Japan’s government has never formally apologized for the actions of Unit 731, even as evidence mounts and international calls for accountability grow louder.
Shimizu’s personal journey is both harrowing and emblematic. He joined Unit 731’s Youth Corps at just 14 years old, arriving at the unit’s headquarters in Japanese-occupied Northeast China in early 1945, mere months before the war’s end. In an interview with NPR, Shimizu recounted his initial naivety. He expected to be given a manufacturing job, but was instead confronted with scenes that would haunt him for the rest of his life. “The most shocking thing for me was a specimen of a whole female body with a fetus in its womb,” he recalled. The headquarters, he said, was filled with jars containing human organs and other grisly evidence of medical experimentation.
Unit 731 and its associated branches—such as Unit 1644 in Nanjing and Unit 8604 in Guangzhou—were responsible for some of the most egregious war crimes of the 20th century. Between 1936 and 1945, these units conducted experiments on live prisoners, often without anesthesia, infecting them with deadly diseases and using them as human test subjects for biological weapons. The victims, mostly Chinese civilians and prisoners of war, were dehumanized to the point where Unit 731 doctors referred to them as “maruta,” or logs. “I did not see any of the maruta alive,” Shimizu said. “All I did was collect their bones and put them in a bag, after they had been killed and their bodies burned.”
Estimates suggest that Unit 731 alone killed around 3,000 people, while bioweapons developed by other branches are believed to have killed many more. Despite this, Japan’s official stance remains one of denial. The government insists it has found no evidence that Unit 731 experimented on Chinese prisoners, even though a Tokyo court ruled in 2002 that the military had indeed conducted such experiments and waged biological warfare.
Shimizu’s willingness to speak out has made him a controversial figure in Japan. While some, like local museum curator Hideaki Hara, support his efforts to confront uncomfortable truths—“Our role as perpetrators is not often discussed. People don’t want to talk about it,” Hara told NPR—others criticize him for what they see as disloyalty to his country or its sanitized wartime narrative.
The new trove of military documents, released by Japan’s national archives in May 2025, has also empowered descendants of those involved in the program to investigate their own family histories. One such person is 77-year-old Katsutoshi Takegami, who discovered a trunk of photographs belonging to his father, a member of Unit 1644. “If you kill a lot of people, you become a hero and get promoted,” Takegami reflected. “I was worried that my father had done something bad, and that’s how I got started investigating this thing.”
According to NPR, the newly released personnel rosters from Unit 1644 are considered a “treasure” by researchers like Lv Jing, a historian at Nanjing University. These documents are expected to shed new light on the structure and scope of Japan’s germ warfare system, which stretched from northern China to Singapore. The units operated under the euphemism of “anti-epidemic and water supply” brigades, tasked with keeping Japanese troops healthy while deliberately spreading diseases like plague and malaria among enemy populations.
The legacy of Unit 731 is not confined to history books or academic debates. In China, the scars remain raw. The 2025 postponement of the film “731 Biochemical Revelations”—which dramatizes the suffering of Chinese victims—sparked an online outcry. Many questioned whether the delay was an attempt by authorities to avoid diplomatic friction with Japan. “Just because the movie exposes scars, does that mean people should choose to forget that part of history?” asked Liu Jiaying, an anchor for state-run Hunan Satellite TV, in a viral social media video. “This film is not only a retelling of the past but also a warning to the future.”
Justice for the victims of Japan’s wartime biowarfare program has been elusive. After the war, the international Tokyo Trial sentenced seven Japanese officials to death for war crimes, but the leaders of Unit 731 largely escaped prosecution. According to Barak Kushner, a Cambridge University professor of East Asian History, this was due to a secret deal with the United States. The U.S. granted Unit 731’s leaders immunity in exchange for the data from their medical experiments, keeping the details hidden for decades. “It is a lapse of justice to the highest degree,” Kushner told NPR. The U.S. was motivated by Cold War priorities, seeking to harness the scientific knowledge of Japanese (and German) war criminals while preventing it from falling into Soviet hands. “The immunity offered in that situation reflects the tenor of the times, the political situation, and perhaps the limits of what sort of justice was achievable for war crimes in the immediate post-war era,” Kushner added.
For the families of victims and the few remaining survivors, the wounds of Unit 731 have never fully healed. The new evidence, personal reckonings, and public debates sparked by the recent document releases are forcing both Japan and the international community to confront a dark chapter that refuses to be forgotten. As more details come to light, the questions of responsibility and remembrance grow only more urgent.
The story of Unit 731 is a chilling reminder that the unresolved past casts long shadows, shaping not just historical memory but the moral landscape of the present.