Operation End Sweep: A History of Minesweeping Operations in North Vietnam was written in 1977 by staff members of Tensor Industries of Fairfax, Virginia. Tensor prepared this account under the terms of a contract with the Mine Warfare Project Office of the Naval Sea Systems Command which, in turn, responded to a requirement from the Office of the Chief of Naval Operations. Since the study was a security-classified document, it originally saw limited circulation. Tensor's preface pointed out the importante of End Sweep. That operation represented the U.S. Navy's first major minesweeping campaign since the Navy faced the challenge, in 1950-1951, of clearing extensive enemy minefields laid at Wonsan, Korea. The helicopter mine countermeasures systems developed after the Navy's experience in Wonsan saw their first extensive use in End Sweep. Finally, Tensor's authors noted the special problems posed by the shallow depths of North Vietnam's coastal waters and the sensitivity of the mines involved. Ironically, the U.S. Navy originally laid the mines swept by American naval forces off North Vietnam. The Seventh Fleet's 1972 mine offensive severely hampered Hanoi's ability to import war supplies from abroad and was a factor in encouraging Hanoi to negotiate a peace accord with the United States. The mines posed an equal threat to seaborne commerce once America withdrew from Southeast Asia. It is not surprising, therefore, that in the talks leading up to the Paris cease-fire agreement of January 1973, Hanoi demanded that the United States enter into a separate diplomatic protocol in which America agreed to "render harmless" the mines we had laid in the waters of the Democratic Republic ofVietnam. Over the next six months, as the U.S. Mine Countermeasures Force accomplished this work, and American forces withdrew from Southeast Asia, Hanoi continued to wage war against South Vietnam. During that period the United States viewed the minesweeping operation as a means of attempting to influence North Vietnam's behavior. Dr. Edward J. Marolda, Head of the Naval Historical Center's Contemporary History Branch and a well-known historian of the naval war in Southeast Asia, skillfully revised this document for publication and composed an introduction that places these events in historical perspective. I also wish to acknowledge the major contributions made by Sandra J. Doyle, the Center's Senior Editor, in copy editing the study and overseeing its printing. Operation End Sweep describes a classic mine clearance campaign involving the deployment of men, ships, and specialized equipment halfway around the globe to complete a demanding and politically sensitive naval operation. Considering the continuing importance of mine warfare, the Navy's historians publish this account in the hope that it will be of special interest to today's naval professionals. Dean C. Allard Director of Naval History