The action of 1 March 1968 was a co-ordinated attempt by four North Vietnamese trawlers to resupply the Viet Cong and the efforts of Operation Market Time elements to stop them during the Vietnam War. On 28 February 1968, United States Navy SP-2H Neptune aircraft on routine patrol detected a North Vietnamese SL class naval trawler heading towards the South Vietnamese coast from north of the DMZ. By the next morning, three more trawlers were discovered and units of Operation Market Time were deployed for a surprise interception. The suspect trawlers did not fly flags so it was not until the start of the engagement that their origin was discovered. The trawlers were steel-hulled vessels, 100 feet long and armed with 57-millimeter recoilless rifles and machine guns. All four vessels were loaded with weapons and ammunition intended to be delivered to the Viet Cong. American and South Vietnamese forces that engaged in action included the United States Coast Guard cutters , , , , , , , the swift boats , , , , , and , two South Vietnamese navy junks and one patrol boat. Two U.S. Army helicopter gunships also participated in combat as well as aircraft used to fire flares. Background The United States Navy, South Vietnamese navy, and the U.S. Coast Guard, operating under the authority of the South Vietnamese government, established a blockade of South Vietnam designated Operation Market Time to prevent infiltrations of personnel, munitions and equipment by the North Vietnamese government. A twelve mile wide restricted zone existed along the entire South Vietnamese coast and ships assigned to Market Time had the authority to stop and search any vessel within the zone for contraband material and check the identity papers of any person on a detained vessel. Action Action off Bo De River The trawler designated in U.S. Navy records as An Xuyen Province Trawler (map reference #1) was first sighted on 28 February approximately 150 miles east southeast of Vũng Tàu holding a southeasterly course. On the evening of the 29th she changed to a westerly course and USCGC Winona started a covert surveillance. The trawler crossed the 12-mile limit at 0120 1 March and began a run for the beach near the mouth of the Bo De River at 0200. A blocking force placed near the mouth of the river consisted of several Navy PCF's and the Coast Guard cutters Point