In the summer of 1940, bubonic plague erupted in the Chinese city of Xinging. While disease outbreaks in war-torn areas are common, this particular incident may have stemmed from a Japanese military initiative rather than solely from poor sanitary conditions.

Unit 731, a covert Japanese military unit, was dedicated to weaponizing various pathogens. They believed they had succeeded in using fleas and flies to disseminate diseases like plague and cholera among civilian populations. Alongside this, they conducted inhumane experiments on prisoners to refine their techniques.

The Rise of Shiro Ishii

Shiro Ishii, born into an affluent family, was exceptionally bright and earned a medical degree from Kyoto Imperial University. He joined the army in 1920, quickly moving into a commissioned officer role, where he found a passion for research over patient care.

In 1924, Ishii was dispatched to Shikoku to investigate a new mosquito-borne disease known as Japanese B encephalitis. The impact of this illness was devastating:

• It claimed 3,500 lives.
• Hospitals were overwhelmed.
• Fear gripped the populace, causing chaos.
• Local government was paralyzed.

These events sparked an idea in Ishii: imagine if such a disease could be weaponized against adversaries.

By the early 1930s, Ishii had garnered a PhD in Microbiology and was appointed to lead the Epidemic Prevention Research Laboratory. Although the lab ostensibly aimed to protect Japanese soldiers from diseases, its real mission was to engineer epidemics for warfare.

Ishii's ambitions required two key components: a research facility and human subjects. He found both in Manchuria, as Japan invaded this region of China in 1932. Captured prisoners became test subjects, and villages could be repurposed for experimentation.

After some initial setbacks, Ishii's desires were fulfilled, complete with a budget rivaling that of the U.S. Manhattan Project.

Formation of Unit 731

When completed in 1939, Unit 731 resembled a blend of a biomedical facility and a grotesque resort, sprawling over two square miles with over 150 buildings, including laboratories, housing for personnel, and a crematorium.