Prior to 1965, it was estimated that over 70 percent of supplies being brought into North Vietnam was brought in over the sea. After implementing a coastal surveillance patrol this avenue was virtually cut-off. Instead the NVA had to rely on porters, trucks and other supplies via the Ho Chi Minh Trail. This operation was known as Market Time. The North Vietnamese Naval Transportation Group used 100-ton trawlers and junks to infiltrate and supply the South, while the Viet Cong used smaller sampans to operate.
The operational area for Market Time was divided into nine patrol sectors to cover the 1,200 mile coast. An area that stretched from the 17th parallel to the Cambodian border and then out 40 miles. In these 9 sections the U.S. Navy operated boats and the aircraft from bases in South Vietnam, Thailand and even the Philippines. The Coast Guard even joined in on this operation.
The work horse of this operation was the 50-foot Swift boat which was armed with a .50-caliber machine gun and an 81-millimeter mortar. This boat had a max speed of 23 knots. The crew of a typical Swift boat was a skipper, a boatswain's mate, an engineman, a gunner's mate, a radio/radar man and a seaman or deckhand. The biggest benefit of the Swift was it could operate in less than 5 feet of water. (Currently the Swift boat is talked about due to John Kerry running for president in 2004.)
When the operation, Market Time, started it was under command of the Seventh Fleet and known as Task Force 71. There were five bases setup along the South Vietnamese Coast, at Danang, Qui Nhon, Nha Trang, Vung Tau, and An Thoi. Halfway through 1965, command passed to the Naval Advisory Group and created the Coastal Surveillance Force or Task Force 115. In 1966, Naval Forces, Vietnam was formed and control was turned over to that group.
As 1968 came to a close, there were more and radar picket escorts assigned to the group and less and less patrols were required. Also the Coast Guard started dispatching 82-foot cutters to Southeast Asia. Along with the Coast Guard boats the Asheville class patrol gunboat, which was designed specifically for coastal operations arrived on the scene. These boats were capable of 37 knots, carried a .50 caliber gun forward, on 40 millimeter gun aft and four .50 caliber machine guns.
The buildup to the Tet Offensive provided many successes for this operation, the high point of it. There were over 700,000 boats intercepted. Soon after there was no longer a need for Operation Market Time due to the Ho Chi Minh trail being so firmly established and was able to supply the NVA.
Sources inlcude http://www.mrfa.org/tf115a.htm, http://www.mrfa.org/tf115b.htm, http://www.military.com/Content/MoreContent?file=PRherrera1, and http://www.military.com/Content/MoreContent?file=PRherrera2 and the US Navy. An interesting side note is a google search of Swift boat returns almost exclusivly content about John Kerry, it takes awhile to weed through the searches.