From left, U.S. Air Force Staff Sgt. Shamikah Dunnings and Senior Airman Sarah Lowry, 633rd Aerospace Medicine Squadron bio-environmental engineer technicians, assemble a Radeco air sampling instrument and portable generator during an active shooter exercise at Langley Air Force Base, Va., Dec. 19, 2013. Women have filled several key roles in U.S. military history dating back to the American Revolution when they served as battlefield nurses, water bearers and cooks. Today, women serve in nearly every career field in the U.S. Armed Forces and, although women already fill certain combat positions, they are on the forefront of having the ability to serve in all combat professions by 2016. Dunnings hails from Chicago, and Lowry is a native of Derby, Kan. (U.S. Air Force photo by Senior Airman Jason J. Brown/Released)