Craig Manson authors an interesting Blog titled "GeneaBlogie." He recently posted a story about intelligence gathering during the Civil War. With the background being the intelligence the Union derived from Black sources in general, he tells the specific story of Mary Elizabeth Bowser. Mary Elizabeth Bowser has been the subject of scholarly examination, as well as popular history, novels, and plays. In 1995, she became one of just eight women ever admitted to the Military Intelligence Hall of Fame.
To make the story even more intriguing, the facts come from a paper produced by the Central Intelligence Agency itself.
You can read Craig article as well as find a link to the CIA paper at: http://blog.geneablogie.net/?p=1295