Although the berms were prime targets, the ASRT, MATCU, FDC, 26th Marines communications center, and other units which depended on sophisticated and delicate equipment suffered from the heavy shelling. Consequently, they all had one common problem--maintenance. The normal difficulties associated with keeping the various radars, radios, antennae, generators, and cooling components in an "up" status were complicated by the constant incoming, the dust, and the limited supply of replacement items. The vans and bunkers were heavily sandbagged but antennae and some communication lines were exposed and frequently knocked out by enemy rounds.[62](171) The speed with which the vital installations were returned to operation served as a tribute to the technicians who maintained the equipment under the most adverse conditions imaginable. In one instance, a 122mm rocket exploded a scant seven meters from the ASRT-B van and sheared off most of the radio antennae. Thanks to several trouble shooters who braved the intense barrage and repaired the damage, the station was back on the air within 20 minutes.[63] Such performances were routine. The ASRT normally operated 23 hours a day and shut down one hour for maintenance. The MATCU, which was essential for ground-controlled approaches and paradrops, was kept operable 95 percent of the time.(172) Major John A. Shepherd, Communications Officer of the 26th Marines, was responsible for the vast network which enabled the ground commanders to keep abreast of the situation and in touch with their units. The major praised the accomplishments of his men, stating that they "provided support in winning every battle, firing every round of artillery, controlling every air strike, and providing the means to receive every bean and bullet." There were six radio relay teams which kept open 52 channels between Khe Sanh and the outside world. In addition, there were five external teletype nets in operation 24-hours a day. Radio relay provided voice and teletype links to agencies at Dong Ha and Da Nang. For classified information, there were two secure voice circuits operating full time. One net linked the Combat Operations Center of the 26th Marines to that of the 3d Marine Division at Dong Ha. The other, the Regimental Tactical Net, enabled Colonel Lownds to disseminate hot information to his battalion commanders.