Sarah Edmonds
The man known as Franklin Flint Thompson to his fellow soldiers was really a woman - Sarah Emma Edmonds - one of the few females known to have served during the Civil War. Edmonds was born in Canada in 1841, but desperate to escape an abusive father and forced marriage, moved to Flint, Michigan in 1856, where she discovered that life was easier when she dressed as a man. Compelled to join the military out of sense of duty, she enlisted in the 2nd Michigan Infantry as a male field nurse, participating in several battles including Antietam, the First and Second Battles of Manassas, and the Vicksburg Campaign.
Source: http://www.nps.gov/resources/person.htm?id=169
Additional Resources:
http://civilwarsaga.com/sarah-emma-edmonds-female-spy-of-the-union-army/
http://www.civilwar.org/education/history/primarysources/sarah-emma-edmonds-pension.html
http://www.civilwar.org/education/history/biographies/sarah-emma-edmonds.html