If there was anything that could top that performance, it was the spectacular air shows provided daily by B-52 Stratofortresses of the 4133d Provisional Heavy Bombardment Wing, based at Andersen Air Force Base, Guam, and the 4258th Strategic Bombardment Wing in Thailand. The B-52 pilots did not count on finesse as much as they did on sheer power because each Stratofortress carried a 27-ton payload of 108 mixed 500- and 750-pound bombs. Since these giants had the means to virtually move mountains, the Arc Light strikes were used on area targets such as troop concentrations, marshalling points, supply depots, and bunker sites. The result of the enemy build-up around the base was an enormous number of targets located in dispersed but common areas and such complexes were ideal for heavy bombers. These targets were programmed into computers aboard the aircraft and the strikes were conducted from altitudes above 30,000 feet. To the bomber crews, it was an impersonal type of warfare because, from above the overcast, they rarely even saw their bombs explode. The bombs did not have to be seen to be felt.(143) When several flights of B-52s worked over a target, the results were awesome. The exploding bombs churned up strips of the terrain several thousand meters long and the ground for miles around literally shook from the blasts. Many enemy casualties were sustained from the concussion alone. One entry from a captured North Vietnamese diary read: "18 February: The heavy bombing of the jets and B-52 explosions are so strong that our lungs hurt." In some instances, NVA soldiers were found after an Arc Light strike wandering around in a daze with blood streaming from their noses and mouths.[52] Often the internal hemorrhaging induced by the concussion was so severe that it resulted in death. Quite understandably, such missions could not be unleashed too close to the Marines.(144) In the early stages of the conflict, Arc Light strikes were not authorized within a prescribed distance of friendly lines. The same rule had applied during the heavy fighting at Con Thien the year before and the NVA had taken advantage of the buffer zone by moving troops and supplies in as close to the Marine base as possible to avoid the bomber raids. They tried the same thing at Khe Sanh. When American airborne observers noted enemy bunker complexes cropping up near the KSCB, the no-bomb line was moved in to about half of the original distance. At first the regimental commander was afraid that the resulting concussion would collapse his own bunkers and trenches; as it turned out, the enemy fortifications were the only ones which suffered. The first few B-52 raids inside the old line touched off scores of secondary explosions and undoubtedly snapped the North Vietnamese out of their sense of security. The closer strikes also served as a morale booster for the defenders who flocked from their bunkers to watch, what the Marines called, "Number One on the hit parade."(145)