Again the massive vehicle descended into the depths. The roaring became louder with every foot and the constantly dinning noise rattled the earphones of the crane and carrier operators. Hall stood on the bank, his eyes glued to the thread of cable vanishing beneath the waters. The tractor was bumping against the wall with more violence and the engineers could feel it tip and sway as the turbulence increased from below. "I think we're too close to Number Two pump," Alec yelled. "Let's get a little more offshore." On the far bank, Number Two crane began hauling the pulley towards him. The undersurface bobbing lessened. "That's good, Number Two," Alec shouted. The downward motion continued. As suddenly as it began, the turbulence almost ceased and the sound diminished in the black, watery hole. The big nuclear pumps stood thirty feet high with their great jets at the top. The tractor had descended blow the level of the jet thrust. At the same instant, there was a forward motion and the tractor began to sweep toward the downstream wall of the bore. "Drop us, fast," Alec commanded. "We're being sucked." Number One crane operator slammed his release button and the tractor fell with a jarring crash to the floor of the catch basin. On the floor, its mass held it in place against the drag of the three huge pumps and the natural flow of the water. The water was clearer and their lights penetrated a few feet into the black-green hell around them. "You see it?" Alec asked his partner. "Not a thing," Troy replied, "but we can't be more than a few feet from it. It's got to be somewhere in front of us and I think a little to my side. The suction drag doesn't seem quite so heavy over here." "Number One," Alec instructed, "give us a fast one-foot lift and drop it immediately. The current will move us." The operator took up the slack in the cable and then gave a short burst of upwards pull and slammed the release. The tractor lifted and was carried forward about five feet before it slammed down again and stopped. "There it is," Troy yelled, aiming his light to the right front of the tractor. The beam picked out the massive casing of Number Four pump. "Let's get in close." On instructions from the submerged engineers both cranes lifted and hauled briefly. The tract slammed into the bulk of the disabled pump. Troy and Alec played their lights over the plate. "This is the bottom plate," Alec said. "It's tipped all right. Got to ease around to one side." Again the cranes dragged and lifted and the massive tractor scraped along the bottom plate of the overturned pump. Suddenly the vehicle whipped forward. "Drop it," Troy yelled, and the carrier smashed to the basin floor. They were alongside the main outlet tube, now tilted downwards on an angle towards the floor of the basin. Below them and under the curvature of the tube was the pile housing. The explosive had to be placed at the point where the pile housing, the pump base and the outlet tub met.