IN THE SUBMARINE "Q-4"
each holds just enough water to fill in around the torpedo."
"But why not draw the water from the outside?" asked Nelson.
"Because you'd add about seven hundred pounds of weight to the boat and start her sinking. You see, you've got to maintain the same stability. When you fill around the torpedo with water from the tank you're not taking on any more weight, you're only shifting it from one place to another, and without changing its longitudinal position. Get that?" Nelson nodded.
"Then we open the outer cap and we're ready for firing. We report Number One or Two, or whichever it may be, ready over the tube, and the Old Man just presses a button. Air compressed to a hundred pounds to the square inch butts in through here behind the torpedo and out she goes at thirty knots. Simple, what?"
Nelson smiled. "When you know how. But look here, Townsend. After you've shot your first torpedo where do you get water from to fill the tube around the next one? Your tank's empty, isn't it?"
"Right-o! But listen to me, old settler. When your 'moldie' leases the tube the water flows into it. The weight of that water is only a few hun-
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