U.S. Marines with 1st Battalion, 1st Marine Regiment, Marine Rotational Force – Darwin, train on an over-water obstacle course at Gallipoli Barracks, Queensland, Australia, June 7, 2016. The course is part of a three day period of sustainment training to keep Marines in good physical condition during MRF-D. MRF-D is a six-month deployment of Marines into Darwin, Australia, where they will conduct exercises and train with the Australian Defence Forces, strengthening the U.S.-Australia alliance. (U. S. Marine Corps Photo by MCIPAC Combat Camera Cpl. Jordan D. Walker/Released)