give him alot of grace and love. When he says I don't want to talk about it don't drill him let it go. while he gone on active duty get a daily log what you thinking and doing. Save it when he comes home and share it. As a man we love to know the things that doesn't matter to most. Because its he love thoughts and feelings of our women and that importants.
Please just go with what he tells you. Too many people speculate. There are many different jobs in the military that go beyond branch and unit. What he does may differ greatly from what stories you might hear.
As for what to expect... Expect him to have to be away often. Sorry.
What don't they do. Those guys get dropped in the middle of the worst to do the impossible. You can expect him not to tell you anything about it.
Important stuff which shouldn't be spread around, careless talk costs lives... hush