Francis Clalin
Frances Clalin was a woman who disguised herself as a man so she could fight in the American Civil War. She served for several months in the Missouri artillery and cavalry units.
Primary Sources
(1) Mary Livermore, My Story of the War (1880)
Some one has stated the number of women soldiers known to the service as little less than four hundred. I cannot vouch for the correctness of this estimate, but I am convinced that a larger number of women disguised themselves and enlisted in the service, for one cause or other, than was dreamed of. Entrenched in secrecy, and regarded as men, they were sometimes revealed as women, by accident or casualty. Some startling histories of these military women were current in the gossip of army life.