She began as a nurse on the battlefield of the Civil War but became a (civilian) battlefield surgeon during the war. (She graduated as a medical doctor in 1855 but women weren't accepted for battlefield service - she changed that.) She was awarded the Medal of Honor for her service (the only woman to receive the Medal of Honor).
After the War, she was a supporter of such issues as health care, temperance, women's rights and dress reform for women. (Look at the photo!)