Long story short, some locations are blacklisted for personal travel for active duty service members. I don’t know the exact website for it but I’m sure it’s just a google away.
For your security clearance they don’t care about personal travel as long as you are truthful and it’s not suspicious or with suspicious people. There is a lot that can come from that but there is nothing wrong with traveling Europe.
I will say, if it is during any type of schooling, you are not allowed to take leave during classes so that everyone is on the same page and no one falls behind. I was at Dam Neck for a C school for 160 days and there was no leave, you couldn’t miss more than like 5 class dates for any reason otherwise they’d recycle you to the next class or you’d be dropped. Not sure if with officer it’ll be easier and they’ll be nice, but I doubt it. I’d advise to communicate your travel with your recruiter or whoever your POC is so they can get it documented by an SSO or whatnot, and then plan to be completely available from your ship date to OCS until you arrive at your first duty station.
Hope this helps.
V/R