Marines with Alpha Company, 1st Tank Battalion, advance on a mock enemy position in an M1A1 Abrams during Exercise Desert Scimitar 2014 aboard Marine Corps Air Ground Combat Center Twentynine Palms, Calif., May 11, 2014. A tank’s success on the battlefield is defined by the teamwork of its four crewmen, who each play a vital role. The mission cannot be completed without every member. Each crewman has a specific yet equally important job required to operate the vehicle. (U.S. Marine Corps photo by Cpl. Christopher J. Moore/Released)