A U.S. Marine changes his socks after a hike during Mountain Training Exercise 2-17 at the Marine Corps Mountain Warfare Training Center, Bridgeport, Calif., Feb. 25, 2017.

The ASU became mandatory for wear in 2014, replacing the Army dress green uniform, which saw 61 years of service. The service plans to begin issuing the Army Greens to new soldiers in summer 2020.