The most infamous of the Imperial Japanese Army’s Bōeki kyūsui-bu (BO), Unit 731, which conducted biological warfare and human experimentation, was able to commit these war crimes due to the BO’s organisational structures. As the ‘epidemic prevention and water purification’ organisations, the BO were tasked to support field forces in limiting disease spread and providing potable water. The combination of these tasks, along with an organic medical supply unit and a culture which gave authority and autonomy to medical officers, was unique in the world. However, when these BO organisations were employed at different echelons throughout the Japanese Empire, nearly all failed to accomplish their mission in a field setting. The ‘successful’ BO organisations were those that exploited the system and conducted human experimentation war crimes. Grounded in centuries of military history, Japan’s development of its national standing army coincided with a larger global trend of specialisation and professionalisation, in both the military and medical fields. Using Germany as its model, Japan was able to quickly develop a capable military in a short time. Victory in the Russo-Japanese War and the acclaim from around the world, led Japan to keep its army structures as they existed at the end of the war where they were never meaningfully critiqued or analysed for potential organisational weaknesses. As Japan moved into World War Two, the unique environment created by the authority and autonomy of conscripted medical professionals with easy access to medical supplies, led some BO organisations to commit human experimentation crimes. Ultimately, Japan’s lack of oversight, either military or civilian, allowed medical officers free reign to conduct whatever research they believed was in the military or the nation’s best interest, resulting in the human experimentation war crimes of Unit 731.
Valerie Jeanine Cranmer (2026) studied this question.