Electronic Countermeasures in the Air War Against North Vietnam is one of a series of monographs on USAF tactics and techniques in Southeast Asia. Electronic countermeasures is but one aspect of the broad subject of electronic warfare, which was waged in all its complexity throughout Southeast Asia. Nevertheless, in choosing to deal with this topic, the Office of Air Force History faced a difficult security problem, for key material is so closely held that its inclusion might result in a history to which the average Air Force officer would not have access. As a result, this special intelligence was not used. Instead, various agencies involved in electronic countermeasures, having access to material not available to the historian, were invited to comment on a draft of the monograph, to ensure an essentially correct account. The author did most of his research at the Office of Air Force History, using materials obtained from the Albert F. Simpson Historical Research Center and the Air University Library, Maxwell AFB, Ala. The U.S. Air Force Security Service, (USAFSS), San Antonio, Tex., furnished certain countermeasures evaluations that did not contain unusually sensitive information. Data from this organization supplemented the material assembled by the Strategic Air Command, Offutt AFB, Neb., on the 1972 B-52 campaign against North Vietnam.