Unit 731. In north-east China during the Second World War, the Japanese army built a complex of research laboratories to develop deadly microbes, such as cholera, anthrax and bubonic plague, into weapons of mass destruction. These were tested on human guinea pigs, many hundreds of thousands of whom died. Anita McNaught follows some of the surviving victims - Chinese PoWs and civilians - as they seek compensation from the Japanese government. Producer Giselle Portenier: Editor Fiona Murch