The B-52 D/F long range bombers (shown below) were designed to carry nuclear weapons but some were reconfigured and used in the VIETNAM war to drop "Iron Bombs". Their normal bomb load was 84 bombs internally and 24 bombs under the wings. Each bomb weighed 500 pounds. (Sometimes they carried 750 lb bombs.) That's 54,000 pounds of HE, a lot of bang from each aircraft.
Crews and aircraft from the 22nd, 91st, 99th, 306th, 454th, and 461st Bomb Wings rotated through the bombing campaign. Flying out of Andersen Air Force Base on Guam Island (and later U-Tapao Base in Thailand) they had sufficient range to drop their loads on VIETNAM and return without stopping. However to increase their bomb load they normally took off with less than full fuel tanks and refueled in mid-air west of Luzon.
These aircraft worked in threes (called cells) and their attacks were called "Arc Lights". The bombs punched 50 ft holes in the ground and cleared away a lot of jungle. They did not, however, kill great numbers of NVA. Often warned by Russian "Trawlers" sailing near Guam and using state of the art radio intercept equipment, the NVA forces frequently moved out of the target area shortly before the bombs arrived.