The Women's Memorial at Arlington National Cemetery exhibit: Clandestine Women: Untold Stories of Women in Espionage.
This excerpt is from suffragette Harriot Stanton Blatch's work, Mobilizing Woman-Power.
"War compels women to work. That is one of its merits. Women are forced to use body and mind, they are not, cannot be idlers. Perhaps that is the reason military nations hold sway so long; their reign continues, not because they draw strength from the conquered nation, but because their women are roused to exertion. Active mothers ensure a virile race.
The peaceful nation, if its women fall victims to the luxury which rapidly increasing wealth brings, will decay. If there come no spiritual awakening, no sense of responsibility of service, then perhaps war alone can save it. The routing of idleness and ease by compulsory labor is the good counterbalancing some of the evil".
Officer, Nurse, Woman by 
American Women in World War I by 
Women Military Pilots of World War II by 
Women and War in the Twentieth Century by The United States Army has been giving credit to women soldiers since 1775. Margaret Corbin replaced her husband at putting ammunition in the cannon during the Revolutionary War in 1776 after he was fatally wounded. She continued in the battle until she was wounded, and was awarded a pension by Congress in 1779.
The United States Army Women's Museum has been in existence since 1955, and honors these early women soldiers, as well as contemporary ones.
The Army website keeps a list of current demographics posted, which show that as of 2011, women comprised 16% of cadets.
Here's a poster promoting Women's Army Auxiliary Corps (WAAC) which you can see digitally, and the hard copy is available on the 5th floor of the King Library in Special Collections & Archives. The Army website points to three works that are available digitally on the Women's Army Corps, one by Judith A. Bellafaire, another by Mattie E. Treadwell, and another by Bettie J. Morden.
During WWII, there was a shortage of pilots, and women pilots filled the void. Cut loose abruptly after the war, these fly girls didn't recieve any recognition until the 1970s, and were recently awarded a Congressional Gold Medal, although for many, the award came posthumously. Texas Woman's University Libraries received the archival collections of our WWII WASPs.
Image from the Texas Women's University Library
Opha Mae Johnson was the first to join the Marines in 1918, but women found a real role within the Marines when the Marine Corps Women's Reserve was established in 1943. For more on the history of the Marines, visit the Marines' History Timeline or the Women Marines Association.
Female Navy enlistees were heavily used during WWI, predominately to fill clerical shortages, and largely fell away from service after the war had ended. They came back during WWII, and have continued since. The image below is of nurse Lieutenant Ann Darby Reynolds, USN, who was awarded a purple heart during the Vietnam War era, in 1964.
