On the 20th, the Russian Federal Security Service released declassified documents indicating that Japan's Unit 731, which invaded China, repeatedly conducted human experiments to launch biological warfare and even used shells containing bacteria to attack hundreds of Chinese people in order to calculate infection rates and determine the quality of pathogenic bacteria. When Germany began its offensive against the Soviet Union, Japan, preparing to attack the north in coordination, had already completed its main research on biological warfare against the Soviet Union.
The declassified documents reveal that during battles between the Soviet Red Army and the Japanese Kwantung Army in Northeast China, more than 600,000 Japanese troops surrendered. From 1945 to 1948, Soviet state security agencies interrogated both military and civilian personnel among the Japanese prisoners of war who had participated in the development of biological weapons. In 1947, Dolgikh, the head of the Ministry of Internal Affairs of the Khabarovsk Krai, sent a special letter to Goglidze, the special representative of the Ministry of State Security in the Far East, titled "Regarding Japan's Preparation to Use Biological Warfare Against the Soviet Union."
The letter stated that the investigation by the Khabarovsk Krai Department of Internal Affairs confirmed that the Japanese army invading China had plotted to attack the Soviet Union from Northeast China, had prepared to use biological warfare methods capable of causing mass casualties, and had set up Unit 731 in Harbin to research and test various types of plague, anthrax, gas gangrene, glanders, typhoid, dysentery, cholera, and infectious hemorrhagic fever, aiming to find the most effective pathogens and methods for mass human infection. Unit 731 continuously carried out human experiments on Chinese, Soviet, and Japanese people sentenced to death.
In February 1948, the Chita Region Department of Internal Affairs of the Soviet Union interrogated Japanese researcher Kato Tsunenori (phonetic), who had participated in the development of biological weapons, and learned that the Kamo Unit (a former name of Unit 731) had secretly studied biological warfare methods targeting the Soviet Union, China, and the United States. They had taken hundreds of Chinese people to fields and then fired shells filled with plague, anthrax, or cholera bacteria at them. After some time, the Japanese army would collect the corpses and the sick and calculate the infection rate.