See A. Ind, A Short History of Espionage (1963); R. W. Rowan and R. G. Deindorfer, Secret Service: Thirty-Three Centuries of Espionage (rev. ed. 1967); R. Friedman, Advanced Technology Warfare (1985); G. Treverton, Covert Action (1989); J. Keegan, Intelligence in War (2003); M. J. Sulick, Spying in America (2012).
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.