The Marines were also faced with another question concerning their defenses: "How large an artillery round could you defend against and still remain within the realm of practicality?" Since the 26th Marines was supplied solely by air, building material was a prime consideration. Matting and sandbags were easy enough to come by but lumber was at a premium. Fortifications which could withstand a hit from an 82mm mortar were a must because the North Vietnamese had an ample supply of these weapons but the base was also being pounded, to a lesser degree, by heavier-caliber guns. With the material available to the 26th Marines, it was virtually impossible to construct a shelter that was thick enough or deep enough to stop the heavy stuff.(82) This fact was borne out when Colonel Lownds decided to build a new regimental CP bunker. The engineers supplied the specifications for an overhead that would withstand a 122mm rocket; to be on the safe side, the colonel doubled the thickness of the roof. The day before the CP was to be occupied, a 152mm round landed squarely on top of the bunker and penetrated both layers.(83) The massing of enemy artillery made the hill outposts that much more important. Had they been able to knock the Marines from those summits, the North Vietnamese would have been able to fire right down the throats of the base defenders and make their position untenable. As it was, the companies on Hills 881S, 861, 861A, and 558 not only denied the enemy an unobstructed firing platform from which to pound the installation, they also served as the eyes for the rest of the regiment in the valley which was relatively blind to enemy movement. For observation purposes, Hill 881S was the most strategically located and a discussion of the enemy's heavy weaponry will point out why.