It must have been during one of these special tours of his, which were by no means without danger, over the rounded slippery side-deck, that the inspiration came to him. In brief, he opened to us the joyful possibility of the "wave-bath."
In order to understand this, it is first necessary to know the construction of the upper part of the "Deutschland." Above the cylindrical hull, on the sides of which are the submersion tanks and oil bunkers, rises the outer ship, which gives the vessel its real ship form.
In this upper part of the outer ship, the so-called "outer tanks" are placed which, when the ship is laden, are always flooded, as water and air may penetrate to their interior by numerous openings, holes and slits, in order that a rapid filling and emptying may be achieved. The "outer tanks," therefore, have no connection with the floating capacity of the boat; they are only the result of the outer construction which above water does not follow the line of the heavy hull and tanks. In spite of their relatively unimportant functions the "outer tanks" must, of course, be accessible from the upper parts of the vessel. This is made possible by large movable steel lids and by ladders on the upper surface of the deck. Standing on the so-called tank-deck, therefore, you have a slight elevation to the upper deck surface. The sea water is continually rushing into these big spaces during the voyage. You have only to climb in through the opened plate lids to enjoy an absolutely safe and delightful sea-water bath.
We did not fail to put this into practice pretty often, and found our bath delightful. There was only one drawback to the business. If, for instance, you entered the sea-water bath for the first time, soon after the boat had risen to the surface, you found yourself not in sea-water, but in an oil bath!
The bunkers, as a matter of fact, never hold quite tight, especially after a long strain of travelling, and so it often happens that as the boat rises to the surface a curious layer of oil breaks through before she reaches the top. This layer of oil is then to be found in the "bath tank," on the lids of the hatches and on deck. Inside the "outer tanks" it naturally remains on the surface of the water, for there it is not able to mix and disperse quickly. It generally remains there a day, sometimes longer, till the oily water is drained off and replaced by new water again. The unlucky man, therefore, who took a bath during this period, emerged but little refreshed and with a shiny nickel-coated skin. This metamorphosis, as can be imagined, caused great amusement among the crew.
The fine weather now was very favourable for submerging tests, which were made practically every day. Everything worked perfectly smoothly, and we felt we could safely approach the American coast and submerge within the three-mile zone.
During one of these submerging tests a wonderful and fairy-like spectacle was presented to us. I had caused the boat to be steered so that the conning-tower lay nearly two fathoms under water. Above, the sun shone brightly and filled the deeps with radiant light. The water was lit by many colours. Around us the sea was of brightest azure blue of an almost dazzling clearness, and transparent as glass. From the window of the conning-tower I could see the whole length of the boat, round which rose twinkling air bubbles, like pearls. In strange, fantastic distinctness the deck lay stretched out before me, even the furthest bow end was visible. Further ahead was a dim-coloured twilight. It seemed as if the bow of the boat was gliding silently through a wall of opal green, which opened up as she moved, and broke into a dazzling radiant-coloured transparency of light.
We were spellbound at this wonderful sight, and the strangeness of the effect was increased by the jelly-fish as they floated through the transparent blue and were caught in the wires of the deck rails, where they shimmered first rose colour, then pale yellow, changing slowly to purple.