Unspeakable crimes committed by WWII Japanese medical personnel experimenting on both civilians and prisoners of war have been well documented.
Read more about: Dr. Shiro Oshii and Unit 731 and Japan Confronting Gruesome War Atrocity
Unfortunately, unlike modern-day Germany that has openly discussed Nazi atrocities, the current Japanese government appears to offer ambivalent views on the matter and even suggest that some aspects in history textbooks warrant revision.
Some years back, PBS ran a documentary about the Japanese experiments on Chinese farming communities. The Japanese actually filmed their experiments of flying over villages releasing plague infected fleas, then subsequently sending in medical teams to do autopsies, even on those who survived the plague.
The Imperial Supreme War Command wanted to develop weapons to aid an invasion of America.