Also, many military personal live in barracks or in base housing. Many are also required to periodically stay at their base overnight, doing a mix of sleeping, standing watch, and doing menial nightly tasks. For most military facilities, there is always someone there on watch, and always someone there to back them up. Those backup people usually have plenty of time to kill and nothing to do.
Add to that the fact that the military isn't a 9-to-5 desk job and its frequent hurry-up-and-wait mentality, and you've got a lot of bored soldiers.