The price of alliance: Anglo-American intelligence cooperation and Imperial Japan’s criminal biological warfare programme, 1944–1947

From 1932 to 1945, Imperial Japan secretly developed the largest state biological warfare (BW) programme of its time, which was unique in its use of biological weapons in warfare and in its inhumane experiments on captive Chinese civilians. After Japan’s surrender, US military intelligence teams searched for any evidence of BW activities, whilst sharing all it could find with its close partner, the UK. Despite the UK offering little intelligence material in return, it secured detailed US intelligence reports on Japanese BW war crimes, and colluded with the United States to keep these Japanese war crimes a secret.