The Vietnam Studies were written to serve as a value in helping the Army develop future operational concepts while contributing to historical records and providing the American public with an interim report on the performance of our troops. This monograph traces the development and notes the progress, problems, successes, and failures of a unique program undertaken by the United States Army- training, advising, and assistance given by Special Forces troops to paramilitary troops and to additional forces. This became a new dimension in ground warfare- the organized employment of a paramilitary force in sustained combat against a determined enemy. Topics in this document include: beginnings of the Civilian Irregular Defense Group program; the CIDG program under the U.S. Military Assistance Command, Vietnam (July 1963-May 1965); the CIDG program begins to mature; combined special forces CIDG on the offensive; unconventional operations; and the Vietnamese Army absorbs the CIDG program.