Since the mid-1930s , Japan invested large resources toward the creation and development of a tremendous arsenal of chemical and biological weapons , aspiring to use them as a means of inflicting mass-casualties on Chinese and Soviet opponents in the event of a war . During the campaign in China , the Japanese military routinely subjected opposing population centers to ruthless attacks by these weapons of mass-destruction , resulting in the deaths of as many as 2,000,000 people . Oftentimes the targets , such as the helpless city of Baoshan , possessed no military value whatsoever ; clogged with refugees fleeing the front and with grossly inadequate medical infrastructure , Baoshan suffered up to 60,000 dead after being hit by Cholera bombs in 1942 . The war against the Soviet Union was to have been little different : after the introduction of the Kantokuen plan , Japan 's Unit 731 , Unit 100 , and Unit 516 began making extensive preparations for similar operations in Siberia
Unit 731
Unit 731
Kantokuen