When I was in the Army we had the LBE suspenders and butt packs and flak jackets, but now they have these vests with all kinds of attachment loops called MOLLE, or some such. I guess the body armor goes under that? They wear so much stuff they move as slow as I do, and I'm a fat old man. I think they carry knives on those vests like some infantry guys carried theirs on their suspenders. The smaller 5" pilot survival knife was popular for carry that way.
Not being familiar with the new stuff, I don't really know, but it would seem that a nice light 5" blade like the Scrapper 5 would be ideal.