Clopton was killed in action on July 2, 1967 at Quang Tri, Vietnam (South Vietnam). He was killed on the first day of a twelve-day operation called Operation BUFFALO. Company B was sent in to reinforce the NVA 324B Division. From Highway 561, they moved north towards the southern half of the Demilitarized Zone (DMZ), around Con Thein and between Gia Binh and An Kha, near a place called “The Market Place”. They made contact with the People’s Army of Vietnam (PAVN) 90th Regiment and found themselves caught in a trap of devastating fire from enemy snipers and machineguns. The 3rd Platoon tried to suppress it, but it continued to intensify. The PAVN’s flamethrowers set fire to hedgerows along the highway, forcing the Marines out into the open. Reinforcements from Company A were not able to move forwards due to the heavy enemy mortar and artillery fire, and both companies suffered heavy causalities. A single PAVN artillery round exploded within B Company Headquarters and wiped it out. Out of nearly four hundred marines, one hundred-ninety were wounded, nine were missing, and eighty-eight were killed, making this the worst one-day loss for the Marines in Vietnam. Fifty-three of the men killed were from Company B, including the Company Commander, two Platoon Commanders, the Forward Artillery Observer, and Forward Air Controller. Clopton was killed in battle by fragmentation wounds from hostile artillery fire. He was twenty-three years old. The result of the entire operation was a United States victory with one hundred fifty-nine total killed, eight hundred forty-five wounded, and one missing on the U.S. side and one thousand two hundred ninety reported Vietnamese soldiers killed plus an additional five hundred thirteen estimated and one POW.