A recent post (https://www.reddit.com/r/wwiipics/comments/nvyfuo/der_heer_en_cabaret_paris_1940/ NSFW) lead me to new information. We often hear about the "comfort women" of the Japanese and most of us know about the brutality of the Eastern Front. The Wikipedia page seems to show that the Nazis had an extensive network of brothels. Why would this be so hidden from history while the Japanese atrocities gain such infamy?
Wikipedia: https://en.m.wikipedia.org/wiki/German_military_brothels_in_World_War_II
There is always more to say and more research to be done but a good place to start with this question might be with this post by /u/commiespaceinvader which deals with at least some of the problematic areas of defining rape, estimating it and reporting/researching it.