Japan’s Deadliest Weapons The end of World War II might have unfolded in far worse fashion—had Japan proceeded with its biological-warfare option. By Norman Polmar Unit 731, a covert biological and chemical warfare research unit of the Imperial Japanese Army, undertook lethal human experimentation during the Second Sino-Japanese War and World War II. Alamy Laboratory of evil: Japan set up its Unit 731 facility outside Harbin, China, in the 1930s. Thousands of human test subjects were used as fodder in grisly experiments. Getty Images Japan’s biological warfare program was the brainchild of Shiro Ishii—who later traded on his expertise to skirt being tried as a war criminal. Alamy