Final answer:
Women formally joined the U.S. Army ranks during World War II, starting with the creation of the Women's Auxiliary Army Corps (WAAC) in 1942, which transitioned into the Women's Army Corps (WAC) with full military status in 1943. Prior to this, women served in the Navy and Marines starting in World War I when nearly 12,000 women enlisted under the Naval Reserve Act of 1916.
Step-by-step explanation:
Women were first officially added to the Army ranks during World War II. The most crucial step toward this inclusion was the establishment of the Women's Auxiliary Army Corps (WAAC) in May 1942, which later became the Women's Army Corps (WAC) in 1943 with full military status. The naval service of women extends back to World War I, where nearly 12,000 women enlisted in the US Navy and Marines under the Naval Reserve Act of 1916.
Initially, the WAAC enrolled women as civilians to work with the military rather than in it. They performed various noncombat roles, from clerical work to mechanical and communications fields. In 1943, the WAAC transitioned to the WAC, recognizing these women as full military members, significantly changing their status and granting them military pay and benefits. Approximately 150,000 women joined the WAAC and another 75,000 served in the nursing corps.