If you are active duty stationed in Europe, do you need a passport to travel or just a leave form and military orders?

Good question. When I was serving (and the Earth was without form) my military ID was the equivalent of a passport.

Ask your squad leader.

Check with your command; it depends on the country you are going to (I assume this is for leave/ a pass?). For non-official travel, a passport and civilian ID is your best bet and should get you in to most countries. A word of warning, though: Make sure your passport was stamped when you entered Europe, even though you just needed your military ID. Me and another guy were nearly detained at the Czech border while returning to Germany. Our story was that we were college kids traveling around (despite military haircuts and bearing), and we had a stamp from Germany in to the Czech Republic - but on further inspection he noted there was no entry stamp in to Germany.