Unit 731 were covert medical experiment units which conducted biological warfare research and development through human experimentation during the Second Sino-Japanese War ( 1937 – 1945 ) and World War II . Unit 731 responsible for some of the most notorious war crimes . Initially set up as a political and ideological section of the Kempeitai military police of pre-Pacific War Japan , they were meant to counter the ideological or political influence of Japan 's enemies , and to reinforce the ideology of military units
Unit 731
Unit 731
Organization of the Imperial Japanese Army