Specifically, my understanding is that warfare during the world wars killed officers at a far higher rate than enlisted soldiers. However, in the various belligerent militaries (Britain, Germany, US, Japan, USSR, China...), how were replacements for officers selected/recruited/trained vs enlisted replacements? I assume they couldn't/didn't just pull promising soldiers out of the enlisted recruitment pool, but it seems to me that replacement would be far more difficult since service academies have both long training times + limited numbers of officers they can plausibly train. Somewhat relatedly, did the quality of officers during the war decline over time as a result of attrition?