As one of the country’s five armed services, the U.S. Coast Guard often is called on to fight wars far from U.S. shores. Tracing its roots back to the 1790 founding of the Revenue Marine, the service’s expertise in littoral operations has played a role in each of the nation’s major conflicts, including the Vietnam War. While many cutters saw combat in Vietnam, one has the distinction of being the last active U.S. warship to sink an enemy in combat: the USCG cutter Sherman (WHEC-720).
Maritime Interdiction in Vietnam
Early in the U.S. involvement in Vietnam, senior military leadership understood that North Vietnam sustained the Viet Cong insurgency in the south through a well-organized supply system. The Pentagon believed that deprived of a steady stream of ammunition and arms, the Viet Cong could be defeated. The Army thought most supplies were sent over maritime routes, but the Navy demurred, citing a lack of evidence.
It was not until February 1965, when an armed North Vietnamese supply ship was interdicted in Vung Ro Bay, that clear evidence of maritime smuggling was discovered. Unmarked trawlers carried supplies from North Vietnam and Hainan, China, to the coastal waters of South Vietnam. Local junks and sampans would rendezvous with the trawlers to ferry supplies ashore. Subsequent intelligence assessments determined that approximately 70 percent of Viet Cong supplies moved via maritime routes. U.S. Army General William Westmoreland, the commander of U.S. Military Assistance Command Vietnam, convened a joint conference in March 1965 to design a naval patrol force to counter infiltration of supplies into the South. This effort was code-named Operation Market Time.
Market Time developed an interdiction strategy around two types of patrol areas: a near-shore zone from the coast out 20 miles, and an offshore zone from 20 to 200 miles. Planners devised grids that were patrolled by U.S. and South Vietnamese vessels and aircraft. To aid in identification of targets, shore-based command centers developed intelligence, surveillance, and reconnaissance (ISR) over likely transit routes. This information was passed to Navy vessels maintaining a constant presence in critical zones. Navy deep-water assets patrolled offshore grids, while smaller, shallow-draft vessels patrolled near-shore areas.
The Navy soon realized that the Coast Guard’s experience in maritime interdiction and the ability of its cutters to operate effectively in shallow-water coastal environments were capabilities needed in Vietnam. By April 1965, the first Coast Guard cutters were preparing for deployment, and by July 1965, they were engaged in combat in South Vietnam. These cutters were 82-foot patrol boats that conducted weeklong near-shore patrols as part of Coast Guard Squadron One, homeported at the An Thoi islands near the Ca Mau Peninsula in South Vietnam. These small vessels were extremely capable. With twin low-maintenance diesel engines, shallow drafts, modern radar, and Loran-C—a radio direction-finding network recently brought to Southeast Asia by the Coast Guard—they could operate in most environments. The cutters also were equipped with communication suites that allowed them to fully integrate with Market Time operations.
By early 1967, the Navy requested an additional five high-endurance 378-foot Hamilton (WHEC-715)-class cutters to relieve Navy destroyers patrolling the offshore zone. These cutters would form Coast Guard Squadron Three, homeported in Subic Bay, Philippines. Hamilton-class cutters, including the Sherman, were able to remain on station for weeks at a time. They were equipped with powerful gas-turbine diesel engines capable of speeds of more than 29 knots and carried large 5-inch deck guns that often were called on to provide naval gunfire support ashore.
The cutters’ primary mission, in both the near-shore and offshore zones, was interdiction. By the end of the war, cutters had conducted 237,490 vessel boardings and were responsible for 90 percent of the trawlers sunk in active engagements. The Sherman’s engagement with the armed trawler SL-3-70 is representative of engagements during Market Time. It highlights both ISR-enabled joint operations and on-scene initiative.
The Sherman’s Action on 21 November 1970
It was a pitch-black night in November 1970, with an unusually high tide flooding the Mekong River’s delta. The North Vietnamese naval trawler SL-3-70 was carrying ammunition and weapons to arm Viet Cong guerrillas fighting U.S. and South Vietnamese troops. The weight of the cargo made it difficult to shift course quickly, and the flooding tide played havoc with the helmsman’s instincts developed over days in the open ocean.
The crew of SL-3-70 were elite members of North Vietnam’s 125th Naval Transportation Group, hand-picked for trawler infiltration duty after months of vetting and ideological indoctrination. All crew members swore to complete the mission at the cost of their own lives, and many displayed this commitment by tattooing their arms with “death before surrender.” The trawler’s commissar understood that the success of an upcoming ground offensive depended on the tons of Chinese-supplied ammunition under his feet. He also understood the sensitivity of the mission, which is why he ordered his crew to rig self-destruct charges in the hold and drilled them on use of the detonator in the pilothouse should capture seem likely.
The mission was nearly complete, although it had been close to failure. A U.S. Navy minesweeper had spotted them while still offshore. After a sharp firefight, SL-3-70 broke the cordon and headed for the designated rendezvous near shore. The shallow water of the delta eventually made it impossible for the old minesweeper to close the distance to the trawler.
The commissar likely was on deck to supervise preparations for the weapons offload and may have seen the faint silhouette of a white vessel, the USCGC Sherman, about 2,000 yards in the distance. He ordered his crew to open fire on the cutter with their 75-mm recoilless rifles and .60-caliber machine guns. Then, three 50-pound 5-inch shells, rigged with impact fuses, slammed into the trawler’s hull, exploding with massive force and likely knocking everyone off their feet.
Captain Paul Lutz, commanding officer of the Sherman, ordered a salvo of air-burst shells to sweep the trawler’s deck and disable her crew. If the vessel didn’t heave-to, Lutz knew he might have to send a boarding team over the rail to take the ship by force, and he intended to stack the deck in his favor.
The Sherman was part of a three-ship Navy task group that had been tracking the trawler for days, using a network of ship-based radar and maritime patrol aircraft. The command ship, the USCGC Rush (WHEC-723), had ordered the Navy minesweeper Endurance (MSO-435) to challenge the trawler once it entered South Vietnam’s territorial waters. Given mechanical issues and draft constraints, the Endurance was not able to run down the vessel. The Sherman’s captain made a pivotal decision to pursue the trawler into the shallow waters of the Mekong Delta despite the risk.
The available charts indicated the Sherman could be standing into shoal waters with a maximum depth of six to nine feet, not enough room for the cutter’s draft. However, Lutz knew that charts of Vietnam’s coastal waters were notoriously inaccurate. During past transits of the same area, the Sherman’s fathometer had shown about nine feet of water below the keel. He also knew there was an extremely high tide that night, suggesting even more water would be under the Sherman. In addition, he was confident in the accuracy of the position fixes his navigator was getting from Loran-C. Lutz ordered maximum speed from the Sherman’s gas turbine engines, about 29 knots, and raced after the trawler.
The Sherman’s fire control radar locked onto the vessel, giving the North Vietnamese little chance of escape; the gun crew waited for the order to fire. Lutz was operating under rules of engagement requiring him first to hail, then to visually identify the trawler as an enemy combatant before attacking. This meant he had to get within visual range but stay beyond the effective range of the trawler’s weapons—about 2,100 yards. Immediately after the Sherman launched flares the trawler opened fire, though most of the rounds fell short. This gave Lutz all he needed to commence firing.
Once engaged, the Sherman’s 5-inch/.38-caliber gun made short work of the trawler. It took just 30 seconds for the first eight shells to find their target. The trawler erupted in a ball of flame and sank. A handful of survivors swam to shore but were picked up a few days later by U.S. troops. Navy divers later surveyed the wreck and found enough ammunition and weapons to arm a division.
The Coast Guard Impact on Market Time
The introduction of Hamilton-class cutters to Vietnamese waters forced the North to shift tactics. By the end of 1971, they stopped using overtly armed steel-hulled trawlers and shifted to small, clandestine, wooden boats with South Vietnamese registrations. These craft had a much smaller cargo capacity and were limited to operating in the near-shore area along the demilitarized zone.
When the last cutter departed Vietnam in 1972, a total of 58 cutters and more than 8,000 Coast Guardsmen had served in theater. Coast Guard combat operations during the war were effective, with more than 2,000 enemy combatants killed in action. While Coast Guard casualties were modest in terms of overall numbers, the service’s casualty rate was more than twice that of the Navy. This probably was the result of boarding and interdiction missions that required cutters to close with the enemy, often leading to surprise encounters.
U.S. forces in Vietnam disrupted a large percentage of North Vietnamese maritime supply attempts and destroyed a significant portion of the North’s fleet. Based on intelligence gleaned from debriefs of a senior North Vietnamese defector, the 125th Naval Transportation Group made 62 successful trips from 1963 to 1972. Market Time forces detected 50 infiltration attempts leading to 37 disruptions (vessels forced to turn back), 11 interdictions (vessels sunk or captured), and 2 successful evasions. Therefore, of 110 known arms shipments, U.S. forces interdicted or disrupted 44 percent. Signals intelligence collected during the war suggests the North Vietnamese trawler fleet consisted of 26 vessels. The 11 interdictions therefore reduced North Vietnam’s available trawler tonnage by 42 percent. These statistics indicate that operation Market Time had a significant impact on North Vietnam’s ability to resupply combat units in the South.
In July 1971, just a few months after the Sherman won its engagement with the North Vietnamese, President Richard Nixon declared the beginning of the “war on drugs.” The lessons in joint operations learned in Vietnam would be applied to a new enemy: drug cartels using vessels to smuggle tons of narcotics from South America to the United States. By the late 1980s, several joint interagency task force organizations would standup using the same basic model developed during Operation Market Time.
Since returning from Vietnam, the Sherman has conducted numerous counterdrug patrols in the eastern Pacific, chasing hundreds of smuggling vessels and seizing multi-ton loads of cocaine. Her crew continues fighting this new war using many of the same techniques first developed in the waters of Vietnam.
Paul C. Scotti, Coast Guard Action in Vietnam: Stories of Those Who Served (Central Point, OR: Hellgate Press, 2000).
U.S. Coast Guard historian, “U.S. Coast Guard In The Vietnam War,” www.vietnamwar50th.com/assets/1/7/U.S._Coast_Guard_in_the_Vietnam_War.pdf.
Alex Larzelere, The Coast Guard at War (Annapolis, MD: Naval Institute Press, 1997).
USCG historian, www.uscg.mil/history/articles/vtn_lutz_sherman.asp.
National Security Agency Cryptologic Histories, series VI, vol. 7, “Spartans in the Darkness: American SIGINT and the Indochina War, 1945–1975” (NSA: 1998).
Ed Vulliamy, “Nixon’s ‘War on Drugs’ Began 40 Years ago, and The Battle Is Still Raging,” The Guardian, 23 July 2011, www.theguardian.com/society/2011/jul/24/war-on-drugs-40-years.
Lieutenant Commander Moe is assigned to the Maritime Intelligence Fusion Center Pacific as the staff cryptologist for Coast Guard Pacific Area. He graduated from the University of Wisconsin, Madison, in 2000 with a bachelor of arts degree in anthropology and Scandinavian studies. He received a Fulbright Fellowship and moved his family to Trondheim, Norway, where he studied maritime archaeology at the Norwegian University of Science and Technology. His research interests include Coast Guard history and intelligence studies.