“All set,” he said. “Okay, you—” he pointed to the young pharmacist, “you go first. Your Lung’s filled with oxygen, plenty of it. There’s the carbon dioxide absorbent in there to take up everything you breathe out. Remember to go up hand over hand, about a foot per second. And don’t be surprised if a couple of guys go floatin’ past you in the water on your way up. There’re other instructors swimmin’ around up there and once in a while one of ’em swims down to see how you’re makin’ out. All set?” “Yes, Chief,” the pharmacist answered. March thought he looked completely calm, though he felt himself growing excited at even this short escape. “Okay, mouthpiece in place,” the Chief said, making sure that the student did it correctly. “Now, nose clips on—that’s right. Finally, open the valve so you can get the oxygen. Okay?” The pharmacist nodded that he was all right. “On your way, then, my lad,” the Chief said. “Duck under.” March watched the young man duck under the water and disappear as he went under the metal skirt. Then he saw the Chief go under, too, right behind him. Up above, he knew, the instructors would see a tug on the yellow buoy fastened to the cable, and would begin their timing of the first ascent. One of them would dive down and have a look at the student coming up, would make him pull away if he were hugging the cable too closely, speed him up or slow him down if necessary, with a gesture and a pat on the shoulder. Suddenly the Chief reappeared. [Illustration: _Hand Over Hand He Ascended_] “Okay, you,” he said, pointing to March. As he put the mouthpiece in place, he thought how strange it was that in the tower in a pair of swimming trunks he was just plain “you” to the Chief Petty Officer, while in uniform outside he would be “sir.” “Right now,” March thought as he adjusted the nose clips and turned the valve, “this man’s my superior and my teacher. A young officer can learn plenty from these boys who’ve had so much experience, if they give themselves a chance by forgetting for a few minutes that they’re commissioned officers.” As the Chief patted his shoulder, March ducked under the water, found the bottom of the round metal skirt, and went under it. Looking up, he saw the long shaft of darkness made by the walls of the tower, and the filmy, cloudy circle of half-light at the surface which suddenly seemed a great distance away. His hands had already found the cable, and he held on to it as he felt the upward tug of the Lung which tried to carry him swiftly to the top. Putting one hand about a foot above the other he began to count to himself, hoping that his counts were about a second apart. For every count he put his hand up what he judged to be another foot in distance. Then he realized that his legs were unconsciously starting to twine themselves around the cable, and he pulled them away, holding his body straight up and down a short distance away from the escape line.