In World War II, Japan created a top-secret project named Unit 731. Officially called the Epidemic Prevention and Water Purification Department of the Kwantung Army, Unit 731 carried out human experiments on unwilling subjects.
Japan committed many horrors throughout WWII, but arguably the most gruesome acts occurred in Unit 731. Located in the Pingfang district of what is now China, most of the test subjects for Unit 731 were Chinese.
By the end of WWII, as surrender became imminent, the Japanese involved with Unit 731 attempted to destroy all evidence of the acts they committed. Unlike their German counterparts, the scientists running Unit 731 were never punished for their human experimentation. It would be many years before witnesses started speaking out about the unit, and only now does the public understand what really went on there.