In April 1968, in the same issue that featured a half-dozen articles on the assassination of Martin Luther King Jr. earlier that month, LIFE magazine published an article on Operation Pegasus, a joint U.S. and South Vietnamese push by 30,000 men "led by the 1st Air Cavalry Division to lift the siege of Khe Sanh. While an armored column rumbled along Route 9, a slender but strategic highway (see slide #4 in gallery), fleets of helicopters lifted men and artillery into the hills above the remote plateau where 6,000 U.S. Marines had been cut off since January."
The relief force found the earth churned into a moonscape by 110,000 tons of U.S. bombs [LIFE wrote]. But they saw little of the two North Vietnamese divisions that had been besieging Khe Sanh. Either the U.S. bombing—the most intensive in the history of warfare—had blasted them out or they had never intended to pay the price in lives that an all-out assault would have meant.
In that article, LIFE published a small handful of photographs by the great Larry Burrows—including the extraordinary first slide in this gallery. Many, many more of Burrows' photos from Operation Pegasus and central Vietnam in the spring of '68 never made it into the magazine. Here are some of those pictures.
Liz Ronk, who edited this gallery, is the Photo Editor for LIFE.com. Follow her on Twitter @lizabethronk.