U.S. Marine Corps Lance Cpl. Alexa M. Hernandez, a

U.S. Marine Corps Lance Cpl. Alexa M. Hernandez, a combat photographer with Headquarters Battalion, 1st Marine Division, wears a gas mask during exercise Steel Knight (SK) 2019 at Marine Corps Base Camp Pendleton, California, Dec. 2, 2018. SK is an annual exercise used to enhance the Marines' and Sailors' skills, tactics, and combat readiness by performing in various dynamic scenarios, ground combat maneuver operations, and live fire ranges. (U.S. Marine Corps photo by Pfc. Frank Cordoba)