Between September 4 and September 12, 1967, multiple North Vietnamese Army regiments laid siege to the vital U.S. Marine Corps base on Cồn Tiên, a hill just two miles south of the Demilitarized Zone (DMZ). Over the following two months, North Vietnamese artillery brought down thousands of heavy explosive shells on the several Marine battalions stationed at Cồn Tiên. A months-long, relentless artillery barrage combined with Communist ground attacks and pelting monsoon rains made the fight for Cồn Tiên one of the toughest battles of the war.
In the spring of 1967, North Vietnam intensified its attacks across the DMZ and began a buildup of forces in the region north of I Corps. By the summer, some U.S. military leaders believed the enemy buildup was a sign that the North Vietnamese intended to launch a massive invasion into northern South Vietnam. In response, the III Marine Amphibious Force received orders to construct a strong-point obstacle system across from the DMZ and to man a series of outposts to block key infiltration routes into South Vietnam. Cồn Tiên was one of these outposts. Cồn Tiên also protected the large Marine Corps logistics base at nearby Đông Hà.
By the late summer and early fall, Marines engaged more and more frequently with North Vietnamese army forces around Cồn Tiên. Communist artillery fire from across the DMZ began to rain down on Cồn Tiên's defenders, and enemy troops launched a succession of ground attacks-including one on September 13 that reached the base's perimeter-all of which the Americans successfully repulsed. During the month of September, the Marines on the hill endured over 200 enemy artillery shells per day. The most intense bombardment occurred between September 19 and 27, when over 3,000 enemy shells hit the base, causing numerous American casualties.
Ceaseless rain, ankle-deep mud, and weeks of relentless tension due to the constant threat of attack and death made the defense of Cồn Tiên one of the most harrowing battles of Vietnam. While the Marines on the hill steadfastly defended the base with artillery, automatic and small-arms fire, and ground counterattacks, nearby U.S. troops aided their countrymen with one of the most focused and potent air and fire support operations of the war. A constant stream of Marine helicopters brought in supplies and ammunition by air, and the Air Force launched over 4,200 sorties against the forces attacking Cồn Tiên. Navy vessels offshore fired more than 6,100 shells, and nearby Army and Marine Corps artillerymen fired an additional 12,500 shells against the attackers, all before the end of October.
Under this onslaught of U.S. firepower, the North Vietnamese finally withdrew back into North Vietnam. Allied officers later estimated that Communist troops had sustained several thousand casualties. But American casualties were heavy as well, with approximately 1,800 men killed or wounded in the defense of Cồn Tiên. The 2nd Battalion, 4th Marines was among the hardest hit units. It numbered 952 Marines in early September, but was reduced in strength to about 300 by the end of October.
The expected North Vietnamese invasion of I Corps never came. Instead, Communist troops launched the Tet Offensive throughout hundreds of cities and towns across South Vietnam in early 1968.