The North Sea rolls in long swells against us. The weather is clear and the wind blows sharply from N.N.W.

I am standing alone with my first officer on duty on the conning-tower, in the "bath-tub," for thus we have nicknamed the strong shelter which is built round the conning-tower hatch of the "Deutschland," and which looks like a kind of flying gondola. In front of this is the upper steering station, which can, however, only be made use of in fine weather.

To-day we stand in oilskins behind the shelter, for the sea is already quite rough enough to wet everything through. The deck is continually swamped, and every minute the waves break over the tower.

I listen with the speaking-tube to the control-room in my hand, while the helmsman growls commands through the telegraph to the engine-room. A dull roar, the bow dips down, foaming, and the waves rush over the deck and dash high against the conning-tower. As quick as lightning we close the hatches and duck in our crackling oilskins behind the shelter ... this little game is repeated every five minutes. Between whiles we stand up, listening to the wind rattling in the stays of the masts, and look around us.

For some time the German coast has faded from sight behind us in the S.E., and the accompanying torpedo-boat which travels in front of us is the last bit of the Homeland. Soon we approach the last line of German outposts; four look-out vessels pass by us in single file and signal us "Pleasant voyage."

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!"

By the gauge I can follow the depths we are making. Through the flooding we have added several tons of dead weight to the boat. We have made the closed up ship's body heavier than the mass of water displaced—and our giant fish sinks—almost falls—into her element down below.

At the same time we are moving with the electric engines, and the forward thrust of the propeller brings pressure and reaction upon the diving rudder, and transforms the sinking into a downward gliding movement.

When the desired depth is reached, which I can tell at once from the depth gauge, further sinking is prevented by the simple means of making the boat lighter again through pumping out the superfluous water from the submersion tanks.

The furious working of the pumps is thus always the sign that we are approaching the desired depth. Then it stops, only the electric engines continue humming, and from the control-room comes the announcement: "We are lying at eleven fathoms."

"Boat is trimmed!"

We are travelling at a depth of eleven fathoms. This means that we are practically blind and can only judge our way by the depth gauge and by the help of that carefully protected boat's treasure—the gyro-compass.

No glimmer from outside now reaches us; the periscope has long been swallowed up, and the steel safety shutters in the windows of the conning-tower are tightly closed. We are entirely transformed into the character of a fish.

Now the communications from all compartments, control-room, engine-room, stern-room, bow-room, holds, accumulator rooms, come through without a hitch. We can travel safely with our "Deutschland" in the deeps.

It is not always, however, such an easy matter to bring a boat of this size down to a prescribed depth. The changes in the specific weight of the water, owing to varying temperatures or to the different proportions of salt held in solution, play a very important rÔle. How strong an influence this can prove I will show in the difference between the Baltic and North Sea waters.

The specific gravities of the two seas are in the proportions of 1·013 to 1·025. This difference in itself may not appear very considerable. With a boat, however, of the size of the "Deutschland," for the submersion of which a very heavy excess weight of many tons is necessary, very important consequences are bound to follow from this difference in specific gravity. Thus in order to submerge in the heavier waters of the North Sea it is necessary to make the boat at least seventeen tons heavier than in the Baltic, as otherwise we should not sink.

Moreover, during sudden alterations in the temperature of the water in the bays and river mouths, where the lighter fresh water comes in, the most unpleasant surprises often occur.

Many a U-Boat commander has thought it possible with a certain amount of excess weight to submerge without difficulty and to keep his boat at a fixed depth. Suddenly, however, the pressure gauge registers a greater depth and the boat drops in the water, like an aeroplane which has fallen into an air-pocket, until a test of the specific weight and temperature of the water gives the clue to her behaviour.

It will therefore be seen that such measurements are necessary before the commander can count with certainty on being able suddenly to submerge and as suddenly to reappear above the waters.

In the meantime we have finished our submerging test satisfactorily. All has gone well and each part fully performed its functions. We are in complete control of our complicated apparatus.

Now the command to reappear is given, the diving rudders are set to "up," and immediately I am able by the depth gauge to follow their working and that of our stout pumps.

After assuring myself that there is no noise of propellers to be heard anywhere in our vicinity, and that on all sides there is no likelihood of collision with any steamer, we pass through the dangerous "blind moment." By this I mean that space of time during which the boat has risen so high that she could be rammed; while, on the other hand, she is still too deep under the water to get the periscope above the surface and take a look round.

This lasts a few minutes. I stand at the periscope and watch. Already the field of vision is lighter. Silvery air bubbles rise up glittering; a blinking and twinkling appears on the glass. Then it is day. A picture arises, clear and shining. The North Sea sways before my eyes with an empty and endless horizon.

Now we are rising to the surface. By the use of the rudder the boat pushes forward faster and faster to the surface of the water. In order to accelerate the ascent compressed air is forced into one of the submersion tanks.

Now she moves very rapidly: the tower is already free. The deck rises dripping out of the water, the conning-tower hatch is opened, fresh air streams in, and I give the command:

"Blow out ballast tanks!"

A wild howling and screeching comes in reply from the control-room, while the powerful turbine engine presses the water out from the submerging tanks.

This does not take long. As soon as a tank is empty the excess air rushes out with a pleasant sound at the side of the boat, and we are soon in normal floating trim again.

We are still using electricity. Now comes last of all the starting up of the heavy Diesel engines by the electric motors. I have already climbed into the conning-tower and can see nothing of all this, except by the communications from the control-room. Those who are in the engine-room, however, will have an exciting spectacle.

The observation engineers stand at their posts. A command comes through the speaking-tube. Everything is ready. Then the chief engineer gives a shrill whistle, raises his hand, two quick wrenches at the switchboard in the electrical engine-room, a couple of blinding flashes half an inch long: the first valve-heads rise slowly, hesitatingly, as if unwilling, then quicker, a wild report and hissing, a wild irregular spluttering, then the loud explosions become rhythmical, and faster and faster both machines resume their regular vibrations.

The submerging test is completed, and pounding along the "Deutschland" proceeds on her way. The wind does not drop, but the weather keeps fine and the visibility is good.

No steamer comes in sight: we can remain comfortably above water. Nevertheless we need to be extremely careful in our navigation.

So the day draws to its end. But as the sun sinks, dark threatening clouds appear, prophesying bad weather for the following day.