Unit 731 was a covert biological and chemical warfare research unit of the Imperial Japanese Army during World War II. Established in 1935, it conducted inhumane experiments on prisoners, including Chinese civilians and POWs, to study the effects of diseases and toxins. The unit's activities included vivisection, exposure to extreme temperatures, and testing of biological agents. The experiments aimed to develop weapons for use in warfare and to advance medical knowledge, but they resulted in immense suffering and death. After the war, many members of Unit 731 were granted immunity by the United States in exchange for their research data, leading to ongoing debates about ethics and accountability.