You stand, then, at the foot of the narrow iron ladder down which you have come from the upper air, you gag your inherited instinct, and let your curiosity loose. Before the boat dives, there is time for a good deal to be taken in. The interior seems large beyond expectation. This is partly an illusion, produced by the vista of the compartments, fore and aft of the central control where you are standing. The bulkhead doors being all open at this moment, you can see into the engine and motor rooms towards the stern, and forward through the battery compartment to the bow torpedo-tubes. The number of men seems large too, and they are all busy; but you note that every part of them is more active than their feet--there is very little coming and going. In the control, close to you, are the captain, a lieutenant, a steersman, and seven or eight other men for working the ballast tanks, air valves, electrical apparatus, and hydroplanes. The last two of them have just come down from the deck--the hatches are closed--engines have already been running for some minutes, though the order escaped your observation. You are invited ‘to see her dive.’ You go up to the forward conning-tower scuttle and flatten your face against the thick glass. An order is given. You hear the hissing of air, as the ballast tanks are filled. You expect to see the forward part of the boat dip down into the water in which she is heaving. Instead of that, it is apparently the sea which lifts itself up, moves along the deck, and seems to be coming in a huge slow wave over your scuttle. The light of day gives place to a green twilight, full of small bubbles. Mentally you feel a slight chill; but physically, a warm and sticky sensation. As there is nothing more to be seen out of window, you return to your instructor. He explains to you that the ship is now running on her motors, and that her speed is therefore low--not nearly enough to overhaul a vessel or convoy of any power. On the surface, with her other engines, she could far more than double the pace; and even with the motors, she could do a spurt for a short time--but spurts are very expensive; for they use up the battery power with ruinous rapidity, and then a return to the surface will be necessary, whether safe or not.