A U.S. Air Force UH-1N helicopter, of the 54th Helicopter Squadron, leads members of the 91st Missile Security Forces Squadron and the 219th Security Forces Squadron as they advance to prevent a simulated assault on a missile launch facility during an intense but routine exercise May 22, 2013, in the Minot Air Force Base missile field complex near Minot, N.D. The exercise is significant because it is a final step in the complete integration of the U.S. Air Force active-duty forces of the 91st Missile Security Forces Group and the Air National Guard’s 219th Security Forces Squadron. The missile field complex covers 8,500 square miles in North Dakota, and the Air National Guard members are interchangeable with the active-duty personnel in the security mission throughout the complex.