Catherine Clinton, Harriet Tubman. (Boston: Little, Brown, 2004).

Virginius Dabney, Richmond: The Story of a City. (Garden City, N.Y.: Doubleday, 1976).

William B. Feis, Grant’s Secret Service. (Lincoln, Neb.: University of Nebraska Press, 2002).

Edwin C. Fishel, The Secret War for the Union. (Boston: Houghton Mifflin, 1996).

Philip S. Foner, History of Black Americans from the Compromise of 1850 to the End of the Civil War. (Westport, Conn.: Greenwood Press, 1983).

Ervin L. Jordan, Jr., Black Confederates and Afro-Yankees in Civil War Virginia. (Charlottesville: University Press of Virginia, 1995).

Jay Luvaas, “The Role of Intelligence in the Chancellorsville Campaign, April-May, 1863,” Intelligence and National Security, Vol. 5, No. 2, April 1990.

Donald E. Markle, Spies and Spymasters of the Civil War. (New York: Hippocrene Books, 1994).

Peter Maslowski, “Military Intelligence Sources During the American Civil War: A Case Study,” “The Intelligence Revolution: A Historical Perspective,” Proceedings of the Thirteenth Military History Symposium, U.S. Air Force Academy, Colorado Springs, Colorado, October 12-14, 1988., edited by Lt. Col. Walter T. Hitchcock, USAF., Washington, D.C.: Office of Air Force History, United States Air Force.

James McPherson, Battle Cry of Freedom. (New York: Oxford University Press, 1988).

David Hepburn Milton, Lincoln’s Spymaster. (Mechanicsville, Pa.: Stackpole Books, 2003).

Frank Morn, The Eye That Never Sleeps: A History of the Pinkerton National Detective Agency. (Bloomington, Ind.: Indiana University Press, 1982).

G. J. A. O’Toole, Honorable Treachery: A History of U.S. Intelligence, Espionage, and Covert Action. (New York: Atlantic Monthly Press, 1991).

G.J.A. O’Toole, The Encyclopedia of American Intelligence and Espionage: From the Revolutionary War to the Present. (New York: Facts on File, 1988).

Ishbel Ross, Rebel Rose: Life of Rose O’Neal Greenhow, Confederate Spy. (New York: Harper & Brothers, 1954).

Meriwether Stuart, “Operation Sanders,” The Virginia Magazine of History and Biography, April 1973, Vol. 81, No. 2, pp. 157-158.

William A. Tidwell with James O. Hall and David Winfred Gaddy, Come Retribution. (Jackson: University Press of Mississippi, 2000).

Elizabeth R. Varon, Southern Lady, Yankee Spy. (New York: Oxford University Press, 2003).

NOTE: A Manual of Signals: For The Use Of Signal Officers In The Field, written by Albert Myer in 1864, can be seen on the Signal Corps Association Reenactors' Division website http://69.3.157.98/SCARD/signalmanual [external link disclaimer]