Another big reason there is less crime on military bases --- there is very stringent gun control, not to mention all other sorts of controls. The military is sort of like a fascist dictator who "makes the trains run on time." Low crime, but less freedom. The typical military base also has a much higher ratio of security to people than most communities can strive for. I would also point out that the military has vastly lower (sometimes almost zero) percentages of populations that are at high risk for crime, such as drug abusers and the poor.

An often recurring problem in military history, however, has been that when troops are exposed to extreme violence and casualties many of the traditional 'peacetime' controls lose their effectiveness. When your platoon has been pinned down and you've been wounded and seen friends die, suddenly threats of NJP (non judicial punishment) seem like so much chickensh*t. As they used to say, "What are you going to do, send me to Vietnam?" These problems are intensively discussed in the military, alas no simple solution has been found yet.