We need to make some more fake cameras like what is in the control room with a flashing LED run by a battery. When they see the cameras, they'll think twice about stealing in the future.
An additional idea is to buy those cheap alarms that you can stick/screw to a door frame and door. As soon as the door is ajar, a high-pitch alarm sounds - like 120 dB. Even a violent vibration will temporarily set it off. The noise alone should cause them to depart the sub quickly... or at least that area. They'll think twice about looting another part of the sub, too.
This is something to keep in mind when the reenactors are aboard, also. If they leave out uniform items and other militaria, it will end up taking a walk during tours - espically if we're all topside scraping paint and laying wood. I think this is one reason why Correy is asking the reenactors to bring a small brass lock with them. I'm not worried about a jacket or a large wool blanket. Pins, hats, photgraphs, magazines, etc. are easy to hide, though.
This may be a local cultural thing, too. Batfish has been looted since she was brought up the river. It's almost like a rite of passage or coming of age. Kids think it's cool if they're one of the people that got away with stealing from the suibmarine. If they hear their dads, uncles, friends, etc. telling their stories of thievery, they'll want to do it, too.