During the early stages of helicopter development, when helicopters were able to lift just slightly more than their own weight, the military services were eagerly seeking to obtain a variety of larger, more useful helicopters. The youthful helicopter industry expressed optimism, although at times unrealistic, in its ability to meet the military requirements. The development of the helicopter program within the Marine Corps was sparked by the foresight and imagination of the officers of the period. While early helicopters provided stepping stones for an orderly progression of the program, the slowness of the technical advances and the periods of financial austerity after World War II and Korea prevented the Marine Corps from developing the vertical envelopment concept as rapidly as desired. The program gained interest and momentum, however, as a result of the success of helicopters in Korea. As Lieutenant General Gerald C. Thomas stated: "Indeed, the helicopter gave clear evidence, from its first tactical employment, that a major advance in combat was at hand." This history, which traces the development of helicopters in the Marine Corps from 1946 to 1962, offers a tribute to the creative vision and planning of a handful of Marine officers who conceived of the vertical assault concept in amphibious operations at a time when suitable aircraft to make it work did not exist. The story of the subsequent struggle to procure and develop those aircraft, to refine a doctrine for their employment, and to familiarize the Marine Corps with their use is an interesting and vital part of modern Marine Corps history. The documentary basis for this monograph was primarily the official records of the Marine Corps and Navy Department, but considerable use was made of interviews and correspondence with key individuals involved in all phases of helicopter development.