Though relatively little official data exists about female Vietnam War veterans, the Vietnam Women's Memorial Foundation estimates that approximately 11,000 military women were stationed in Vietnam during the conflict. Nearly all of them were volunteers, and 90 percent served as military nurses, though women also worked as physicians, air traffic controllers, intelligence officers, clerks and other positions in the U.S. Women's Army Corps, U.S. Navy, Air Force and Marines and the Army Medical Specialist Corps. In addition to women in the armed forces, an unknown number of civilian women served in Vietnam on behalf of the Red Cross, United Service Organizations (USO), Catholic Relief Services and other humanitarian organizations, or as foreign correspondents for various news organizations.