The education board in Nagano Prefecture's Iida city is at loggerheads with local citizens over a peace museum exhibit, as some call for greater focus on "biological warfare" testing on prisoners of war by the Imperial Japanese Army's notorious Unit 731.

Known officially as the Epidemic Prevention and Water Purification Department of the Kwantung Army, Unit 731 undertook covert biological and chemical warfare research in China, engaging in lethal experimentation and testing on humans during World War II.

The special unit, also known as Manshu Detachment 731, was based in the suburbs of Harbin in the puppet state of Manchukuo, now northeastern China, from 1936 to 1945. Prisoners of war were secretly experimented upon to develop, among other things, plague and cholera-based biological weapons, according to historians.