Lieutenant Perry Scope, commanding the X-class flotilla, was sitting in his comfortable little office on the mother-ship _Ozark_, when I entered with a letter from the secretary of the navy, giving me permission to go on board a United States submarine. Without such authorization no civilian may set foot on the narrow decks of our undersea destroyers, though he may visit a battleship with no more formality than walking into a public park. “We’re too small and full of machinery to hold a crowd,” explained the lieutenant, “and the crowd wouldn’t enjoy it if they came. No nice white decks for the girls to dance on or fourteen-inch guns for them to sit on while they have their pictures taken. Besides, everything’s oily--you’d better put on a suit of overalls instead of those white flannels.” There were plenty of spare overalls on the _Ozark_, for she was the mother-ship of a family of six young submarines. Built as a coast defense monitor shortly after the Spanish War, she had long since been retired from the fighting-line, and was now the floating headquarters, dormitory, hospital, machine-shop, bakery, and general store for the six officers and the hundred and fifty men of the flotilla. [Illustration: Photo by Brown Bros. U. S. Submarine _E-2_. Note wireless, navigating-bridge, and openings for flooding superstructure when submerging.] Moored alongside the parent-ship, the submarine _X-4_ was filling her fuel-tanks with oil through a pipe-line, in preparation for the day’s cruise and target-practice I was to be lucky enough to witness. Two hundred and fifty feet long, flat-decked and straight-stemmed, she looked, except for the lack of funnels, much more like a surface-going torpedo-boat than the landsman’s conventional idea of a submarine. “I thought she would be cigar-shaped,” I said as we went on board. “She is--underneath,” answered Lieutenant Scope. “What you see is only a light-weight superstructure or false hull built over the real one. See those holes in it, just above the water line? They are to flood the superstructure with whenever we submerge, otherwise the water pressure would crush in these thin steel plates like veneering. But it makes us much more seaworthy for surface work, gives us a certain amount of deckroom, and stowage-space for various useful articles, such as this.” Part of the deck rose straight up into the air, like the top of a freight-elevator coming up through the sidewalk. Beneath the canopy thus formed was a short-barreled, three-inch gun. “Fires a twelve-pound shell, like the field-pieces the landing-parties take ashore from the battleships,” explained the naval officer, as he trained the vicious-looking little cannon all around the compass. “Small enough to be handy, big enough to sink any merchant ship afloat, or smash anything that flies.” Here he pointed the muzzle straight up as if gunning for hostile aeroplanes.