Unit 516 (第五一六部隊) was a top secret Japanese chemical weapons facility, operated by the Kempeitai, in Qiqihar, Manchukuo. The name Unit 516 was a code name (Tsūshōgō) of the Unit. It was officially called the Kwantung Army Chemical Weapons Section and operated underneath Unit 731. An estimated 700,000 (Japanese estimation) to 2,000,000 (Chinese estimation) Japanese-produced chemical weapons were buried in China. Until 1995, Japan had refused to acknowledge that it dumped chemical weapons in the Yen River in Manchuria, leaving huge amounts behind.