Question: Unit Ei 1644  was established in 1939 in Japanese-occupied Nanking as a satellite unit of Unit 731,  a covert biological and chemical warfare research and development unit of  what army?
Sentence (from "Biological warfare"): Biological warfare (BW)—also known as germ warfare—is the use of biological toxins or infectious agents such as bacteria, viruses, and fungi with the intent to kill or incapacitate humans, animals or plants as an act of war.
Relevant evidence: No