History of blood typing in Japan

[I]n the 1930s, the Army Ministry tasked a university researcher (Kyoto, IIRC) to develop a quick method that could be carried out at draft induction centers to determine which conscripts would be most suitable for assignment to infantry units. The university prof, for some reason, latched onto blood type difference as promising data in this regard. Eugenics, of course, was very much in the air at the time — it being the era of the Nazis and cranial calipers and Social Darwinism and similar creepy, exploitation-legitimizing research. Moreover, as is typical of military bureaucracies everywhere, the Japanese were planning their next war on the expectation that it would be similar — if not identical — to the last, i.e., in this case, a combat environment along the lines of the Western Front in 1914-18 (which Japanese exchange officers had observed and had the you-know-what scared out of them — this experience was also very much the impetus for Yamagata Aritomo and Tanaka Giichi’s initial “総動員” {general mobilization} planning, of course) putting similar psychological stresses on its combatants. In other words, what they were looking for were recruits with the kind of thick-skinned, somewhat passive personality that would enable them to endure long months of immobility in trenches under enemy artillery barrages without turning into nerve-wrecked shellshock cases, and who could best be expected to unquestioningly follow orders to charge into sweeping machine gun fire. The professor determined that people with “O” type blood — whom the doctor characterized as being distinctly “cattle-like” in temperament — would make the best infantrymen for the next expected trenches/gas/machine gun war.

-- 井の中の蛙