Reserve Marines with Company A, 1st Battalion, 23rd Marine Regiment, 4th Marine Division, mount an M2 .50 caliber machine gun atop a hill prior to a notional attack during an air assault course, during Integrated Training Exercise 4-18, aboard Marine Corps Air Ground Combat Center Twentynine Palms, Calif., June 17, 2018. ITX 4-18 provides Marine Air-Ground Task Force elements an opportunity to undergo service-level competency assessments so that they can seamlessly integrate with active duty Marines in the event of a crises that requires a rapid response. (U.S. Marine Corps photo by Cpl. Dallas Johnson/Released)