Unit 516 (第五一六部隊) was a top secret Japanese chemical weapons facility, operated by the Kempeitai, in Qiqihar, Japanese-occupied northeast China.
It was officially called the Kwantung Army Chemical Weapons Section and operated underneath Unit 731.
Until 1995, Japan had refused to acknowledge that it dumped chemical weapons in the Nen River between Heilongjiang and Hulunbei'er, leaving huge amounts behind.
China has started gathering these abandoned weapons for destruction and burial, and they are currently buried in remote Dunhua County, in Haerbaling, Jilin (吉林) province.
Under the convention, Japan is building a factory in China to destroy chemical weapons.