Used in military terminology to describe the mandatory task of providing security or lookout for anything from an ammunition arsenal to an empty barracks. Can last for a few hrs or 24 hrs. Usually given at the worst possible times and weekends to remind you of why you ever joined the military.
Marine: Woot woot!!! It's Christmas, time to go home!!!
1stSgt: Oh fuck no! You have duty Christmas day, don't bother going home.
The most badass and laid back MOS in the Marine Corps. Not always the brightest, but generally good guys to be around. Jobs involve driving big trucks and Humvees, hauling anything and everything, and having 126,362,791 vehicle inspections a month. The saying in Motor T (or Motor Tizzle as it was known in my unit) is "If you can't truck it, fuck it".
Infantry Marine: Oh fuck, why are those guys shooting the shit in their trucks and were out here digging another fuckin fighing hole?!?!!?
Other Marine:Because that's Motor T. Why did I sign up for this shit? It sounded exciting at the time...