"You might prefer to call them decks, Mr. Hythe. Number One is literally on deck, and extends practically the whole length and breadth of the vessel. Her sections are, as you doubtless have observed, almost square, the ridges of the deck and the bilges being very slightly rounded off. This gives plenty of space for the crew when running on the surface, and also enables the ’Aphrodite’ to rest on the bottom of the sea without any perceptible list, unless, of course, the bed shelves at all. Number Two Platform--but perhaps you are not interested?" "Rather!" exclaimed the young officer eagerly. "Well, then, Number Two Platform runs fore and aft at nine feet below the overhead girders, so there is no necessity to have to stoop when in any of the compartments or alley-ways. Number Three Platform rests on the cross girders that are bolted to the keelson, and being airtight form a hollow bottom. As a matter of fact these double bottom compartments are nearly always filled with water, which can be ejected by powerful, quick-delivery force pumps when necessary. Here is the door in the base of the for’ard conning-tower." Unfastening the door by a cam-action lever Captain Restronguet agilely negotiated the narrow way and sprang up a steel ladder. Hythe followed and found himself standing on a metal grating in the company of the captain and a quarter-master. The latter took no notice of his superiors beyond moving a little to one side; his whole attention was fixed upon the task of steering the submerged craft. The interior of the conning-tower was literally lined with electrical appliances, each switch distinctly marked according to the work it had to perform, but for the moment the sub paid scant heed to them. His eyes travelled in the direction of one of three large oval scuttles filled with plate glass. The submersion indicator pointed to thirty-four feet, a depth that allowed the "Aphrodite" to pass under the keel of the deepest draughted battleship afloat, with five feet to spare. The compass pointed due east. "We are just pottering about, as it were, between the Draystone and the Mewstone," announced Captain Restronguet. "The depth here averages ten fathoms, which gives us a margin of five feet under our keel. There is a battleship coming out of harbour, she is now in Smeaton Pass, and we are waiting for her to draw clear. On a falling tide we must take no risks." "What do you mean?" asked Hythe. "Simply that as soon as the vessel is outside the Breakwater I mean to take the ’Aphrodite’ into the Hamoaze, and give you a chance to see that historic stretch of water under slightly different conditions from that which you have been accustomed to, Mr. Hythe. You were in the submarine service, I believe?" "Yes," assented the sub. "But how do you know that?" "Merely by a reference to the Navy List. But look ahead; see that object dead in line with our bows?" "An electro-contact mine, by Jove!" exclaimed Hythe.