I've seen a couple guys go away for a semester and come back to get a nav slot and end up doing engineering (both got what they wanted). So, it's not impossible, but what jetjock says makes a lot of sense. How can you be ranked well for that fall semester when you're not even there? Being that the AF needs engineers, I'd say you probably are ok to do this (assuming your grades and everything are good). Because lets just face it, you don't need to be #1 right now to be an engineer in the AF. Not dogging engineers, but the AF needs them so bad, that they won't really care if you're not in the top 5%. However, having fun abroad is still going to cost you in your ROTC career. If you're not looking to be rated or gunning for DG or something like that, then go for it, have some fun! But if you care about what positions you get in ROTC and your overall class ranking, I'd think seriously about going abroad.