Our faithful companion now approaches nearer; her crew give us three hearty cheers; the officers on the bridge salute; and we two lonely men on the tower return the salute. Then the little black boat ducks into the sea, makes a beautiful turn, stirring up the foaming water at her keel, grows smaller and smaller, and presently disappears, leaving a thin drifting smoke-flag behind her. We are left to ourselves, and travel into the Unknown. Not much time, however, is allowed for thinking. Danger now threatens us from all sides, and I have to make certain that the boat is in good trim, and that I have the engines and submerging appliances well in hand. I give the command, "Clear everything for a submerging test!" At once the response comes back from conning-tower and control-room, and the crew hurry to their submerging stations. The oil engines are still throbbing and hammering. Then the alarm bell is sounded and I spring into the conning-tower; the hatches are closed, and at the same time the oil engines cease working. For a moment one is conscious of a slight pressure in the ears; we are shut up from outside and all is still, but there is no real silence; only a change of sound. Then comes the command: "Open the submerging valves!" "Flood!" What now follows is so strangely impressive that one could never forget it, once having experienced it. The submerging valves are quickly opened, and with a hiss the compressed air rushes out of the tanks. A gigantic volume of air rises, with such an unearthly snorting and blowing that the pressure in one's ears becomes almost painful. Then the noise becomes more even, and is followed by a loud humming and whistling, and all the high notes of the machinery in the engine-room join together and produce a confusion of sounds. It is like the strains of some mad, diabolical music that, after the dull, heavy hammering of the oil engines, gives a momentary impression of unearthliness that is at once penetrating and impressive. This noise in the valves is a sign that the submerging mechanism is at work. The music continues, but in a long downward scale, and during these long drawn out, ever-deepening sounds, one has a bodily feeling as of the rushing in and flooding of mighty masses of water. One seems oneself to grow heavier and to sink with the boat. Through the window of the conning-tower and by the aid of the periscope it is now possible to observe how the front part of the boat is sinking; the railings are cutting their foaming way through the waves, while the water round the conning-tower rises higher and higher, till everything outside is wrapped in the wonderful twilight of the deep. Only our faithful lamps are shining. Now it has indeed become silent. The only sound that reaches the ears is the soft swaying rhythm of the electric engines. Then comes the command: "Go down to eleven fathoms!" "Both engines half-steam ahead!"