Heading "out the gate," or literallythrough the wire, and entering hostile territory while on a combat patrol, such as in Afghanistan or Iraq. "Out the gate" is also the terrain which is beyond the fencelines / walls of your compound.
Johnny Threefingers: "Heard you're getting out of this craphole today."
Harry Hophead: "Pfft...well, I'll be back...you know me, man... ""I’ll be out the gate by eight / in the spoon by noon / fixed by six / and back in the pen by ten!”"