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.