This is the fourth in a series of five volumes dealing with the operations of United States Marines in Korea during the period 2 August 1950 to 27 July 1953. Volume IV presents in detail the operations of the 1st Marine Division and 1st Marine Aircraft Wing, the former while operating under Eighth Army control and also as part of IX Corps and X Corps, USA, and the latter while controlled by the Fifth Air Force. The period covered in this volume begins in the latter part of December 1950, when the Division rested in the Masan “bean patch,” and continues through the guerrilla hunt, the Punchbowl fighting, and all other operations during 1951. The account ends when the Marines move to positions in the west during March 1952. Marines did not fight this war alone; they were a part of the huge Eighth United States Army in Korea. But since this is primarily a Marine history, the actions of the U. S. Army, Navy, and Air Force are presented only sufficiently to place Marine operations in their proper perspective. Many participants in the fighting during this period have generously contributed to the book by granting interviews, answering inquiries, and commenting on first draft manuscripts. Their assistance was invaluable. Although it was not possible to use all the plethora of detailed comments and information received, the material will go into Marine Corps archives for possible use and benefit of future historians. The manuscript of this volume was prepared during the tenure of Colonel Charles W. Harrison, Major Gerald Fink, and Colonel William M. Miller as successive Heads of the Historical Branch. Production was accomplished under the direction of Colonel Thomas G. Roe. Major William T. Hickman wrote some of the preliminary drafts and did much valuable research and map sketching. Dr. K. Jack Bauer and Mrs. Elizabeth Tierney assisted the authors in research, and Mr. Truman R. Strobridge assisted in proofreading and preparing the index. To the Army, Navy, and Air Force officers, as well as Marine officers and NCOs, who submitted valuable comments and criticisms of preliminary drafts, thanks are also extended. These suggestions added to the accuracy and details of the text. Additional assistance was rendered by personnel of the Office of the Chief of Military History, Department of the Army; the Division of Naval History, Department of the Navy; and the Historical Division, Department of the Air Force. The exacting administrative duties involved in processing the volume from first draft manuscripts through the final printed form were ably managed by Miss Kay P. Sue. All manuscript typing was done expertly by Mrs. Miriam R. Smallwood. The maps contained in this volume were prepared by the Reproduction Section, Marine Corps Schools, Quantico, Virginia, and the Historical Branch, Headquarters Marine Corps. Official Department of Defense photographs were used.