Mary Agnes Hallaren was an American soldier and the third director of the Women's Army Corps (WAC) at the time that it became a part of the United States Army. As the director of the WAC, she was the first woman to officially join the U.S. Army.

The Women's Army Corps (WAC) was the women's branch of the United States Army. It was created as an auxiliary unit, the Women's Army Auxiliary Corps (WAAC) on 15 May 1942, and converted to an active duty status in the Army of the United States as the WAC on 1 July 1943. Its first director was Colonel Oveta Culp Hobby. The WAC was disbanded in 20 October 1978, and all units were integrated with male units.