Unit 731 Biological Warfare Network Extended from China to Southeast Asia, Research Reveals

Dragon Media News Desk

Historical records and research have revealed that the notorious Unit 731, operated by the Imperial Japanese Army during World War II, was not confined to Harbin in China but served as the center of a wider biological warfare network extending across several Chinese cities and into Southeast Asia.

Takegami, a 78-year-old resident of Nagano Prefecture in Japan, discovered through old family photo albums that his late father had been a member of Unit 1644, a Japanese military biological warfare formation. He subsequently examined historical records, contacted researchers and traveled to China in an effort to better understand his father’s wartime role.

Research indicates that, with Unit 731 in Harbin as a central hub, the Japanese military operated Unit 1855 in Beijing, Unit 1644 in Nanjing and Unit 8604 in Guangzhou.

The Imperial Japanese Army also established Oka Unit 9420 in Singapore under the Southern Expeditionary Army. Research shows that the unit maintained branches in Malaya, Java, Manila, Indochina and Thailand. These facilities reportedly produced plague bacteria and infected fleas on a large scale to supply biological warfare materials to the Japanese military.

Singaporean independent researcher Lim Shao Bin has spent years investigating evidence showing that Japan’s biological warfare system extended into Southeast Asia. In 2016, during a visit to the former Tampoi Mental Hospital area in Johor Bahru, Malaysia, he learned that the site had been used to produce materials for plague bombs associated with Unit 731. He subsequently began systematically researching the activities of Japanese biological warfare units across Southeast Asia.

After five years of research, Lim and Chinese researcher Wang Xuan published a book in 2025 on Oka Unit 9420. The work provides a detailed historical account of the biological warfare structure operated under the name of the Southern Expeditionary Army’s Epidemic Prevention and Water Purification Department.

Historical evidence indicates that although Unit 731 publicly presented itself as an epidemic-prevention and public-health organization, its actual purpose was to conduct secret experiments on human beings in support of biological weapons development.

Prisoners and civilians were reportedly exposed to plague-infected fleas, injected with pathogens and subjected to extreme cold experiments designed to study frostbite and freezing. Japanese soldiers referred to experimental victims by the dehumanizing term “maruta,” meaning “logs.”

Researchers say Harbin’s extremely cold climate made year-round large-scale breeding of plague-infected fleas difficult. As a result, the Japanese military used warm and humid Singapore as an important production base.

Archival records also indicate that Japanese military researchers isolated a new virus from rats in Singapore and planned to send it to Unit 731 headquarters in Harbin. The records reportedly contain detailed observations of body temperature, symptoms and other data relating to 70 experimental subjects.

Researchers have also highlighted major disparities in postwar accountability. While leading Nazi war criminals were prosecuted at the Nuremberg trials, many individuals associated with Unit 731 reportedly returned to Japanese society after the war and resumed careers in medicine and other professions.

According to researchers, the biological warfare and human experimentation conducted through the Unit 731 system should not be understood solely as a historical tragedy affecting China. It also represents a shared trauma for Southeast Asian countries affected by Japanese military expansion and, more broadly, for humanity.

Lim has called for greater international cooperation in sharing wartime archives, overcoming linguistic barriers and expanding joint historical research.

Researchers argue that, more than eight decades after the end of the war, preserving the shared historical memory of affected countries remains essential. They maintain that confronting the past on the basis of evidence and learning from it are necessary to prevent similar atrocities from recurring and to strengthen the foundations of lasting peace.