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the ocean than any submarine had ever done. I could feel the induced vibration shaking the entire after structure of the ship. The noise of the propellers and the roar of the water as it racedpast our hull were almost as loud as the machinery a few compartments forward.
    “Do you think you could sleep through this, Rowlands?” I asked the husky First Class Torpedoman’s Mate in charge of the after torpedo room.
    Rowlands grinned. “You can sleep through anything if you’re tired enough, sir, but it sure is noisy.”
    “She’ll quiet down a lot when we dive,” I pointed out.
    Rowlands agreed. “But we’ll have to go pretty deep, Captain, to quiet down them spinning wheels with all that power.”
    He was right. The deeper you go, the less noise your propellers make, but the bigger they are and the faster they spin, the more noise they make. Triton ’s propellers, eleven feet in diameter, turning far faster than any other submarine’s, could not avoid making noise at their present shallow depth. But, of course, no other submarine could go as fast on the surface as Triton ; when we slowed down to comparable speeds or when we submerged, the chances were that our ship would be as quiet as the others—perhaps quieter.
    It was nearly time to dive. I hurried forward. Lieutenant Tom Thamm, Triton ’s Diving Officer, was already at his station with his number one diving crew. This entire group had trained together for several months at the submarine dive simulator at Electric Boat and at another, fancier, one in the Submarine Base; but, of course, this was the first opportunity for them actually to dive the ship.
    They were, naturally, somewhat keyed up. The weights in a submarine must be so balanced that when she fills her main ballast tanks the ship will be in precisely neutral buoyancy. Otherwise, she would not be controllable. Naturally, as stores or torpedoes are put aboard, consumed, fired, or unloaded, there are changes in internal weights. These are compensated for by the bow and stern trimming tanks, and by two auxiliary tanks located amidships. These four tanks are known as “variable tanks,” because the amount of water they contain may bevaried. This can be done without danger of rupture due to internal or external pressure. The “ballast tanks,” by contrast, are always open at the bottom, are empty for buoyancy when the ship is surfaced, and must be fully flooded to dive her. One of the trickiest problems in designing a submarine is to calculate the weights and the volumes so that, with all conceivable weights out of the ship, it is still possible to put enough water into the variable tanks to achieve neutral buoyancy. Conversely, she must be designed so that with maximum weight on board, enough water can be pumped out to restore her to neutral buoyancy. (Ballast tanks cannot be used for this, despite the misleading name, for they must always be fully flooded when submerged. Since they are never under any pressure differential, they are lightly constructed, unlike the extremely rugged variable tanks.)
    As Diving Officer, Tom’s job was to work out the compensation under the load condition that existed at any given time, and to calculate exactly how much water was required in each variable tank to insure that when Triton ’s main ballast tanks were flooded, the ship would be both in neutral buoyancy and balanced fore and aft. When the right amounts of water are thus in her variable tanks, the ship, in submarine parlance, is in “diving trim” or “compensated.”
    “The ship is rigged for dive and compensated, Captain,” Tom reported.
    A submarine cannot submerge until it is “rigged for dive,” by which is meant that all the proper equipment for diving is in correct position, either open or shut, in power or set for hand operation as designated, and that every compartment has been inspected, both by the crew members responsible for rigging it and by an officer detailed to check it. There have been