A submarine is a surface ship which can be submerged and driven ahead at a steady depth-line. She is built strongly in order to resist the water-pressure when she is deep down. She is propelled on the surface by (usually) heavy-oil Diesel engines. When submerged she cannot use these, as they consume air, so she has an electric battery and motors for use under water. The battery is charged when on the surface at her convenience or by favour of the enemy. The Diesel engines are used for this purpose, and they recharge the batteries through the motors, using the latter as dynamos.
In old pictures of projected submarines of the seventeenth century one sees that the principle of "trimming down" for submersion was known, and that our present-day system of tanks was intended to be substituted by pig-skins which fitted into cylindrical hollows in the hull. These skins were emptied by screwing out a ram from inside (on the idea of old-fashioned printing presses) which squashed the skins. Nowadays a boat is all tanks along her lower half, the upper half being living space and battery room, etc. These tanks are flooded through valves in order to destroy the boat's buoyancy. The water is ejected from them either by pumps or by the use of compressed air, the latter taking the place of the old seventeenth-century screw-press idea. When the tanks have flooded until the boat's buoyancy is all gone—i.e., until you could press her down or lift her up with one hand—she is "trimmed," and by going ahead and working the bow and stern hydroplanes you can keep whatever depth-line is required. When submerged, a look-out is kept through a periscope—a tube about thirty feet long which has lenses all the way up, is watertight, and has an eyepiece like an ordinary telescope at its lower end.
To dive, a boat opens her vents, puts "dive" helm on, and goes under with her motors running. The flooding valves are kept open to save time; in surface trim a boat is "hanging on the vents"—i.e., if you open the vents (upper valves of the tanks) the water enters and she goes down; until the vents are open the water cannot enter beyond a certain point; when they do open the air in the tanks can get away and the tanks fill up with a rush.
During a trip the "trim" of the boat alters continually. She is using fuel, ammunition, food, and water, and calculation is necessary to allow for this. Certain tanks are used for this compensating, so that on all occasions when a rapid dive is necessary, there is nothing to do but flood the big external tanks, and yet know that the boat will be in hand when under. If mistakes are made, they will show at once. If too much has been put into the "internals" to compensate, the boat will run on down to the bottom in spite of "up helm" and full speed. If too little, you have to flood internals according to an estimate of what is needed as she ploughs along half-submerged; the latter case is one to be avoided, as you may be killed by the enemy while flooding. The usual war practice is to compensate on the "heavy" side—i.e., let her go with a rush and blow tanks so as to catch her and hold her at sixty feet; then you can bring her up to patrol depth at your leisure.
It can be seen, then, that the description of a boat as "bouncing" is not incorrect. When going to the bottom for the night it is a common occurrence, if too rough a "landing" is made, to proceed like a tennis-ball along the sand for a couple of hundred yards. It is a curious thing that both in the Cattegat and the Sea of Marmora, boats have been able to lie for the night with motors stopped at depths of from thirty to seventy feet. In the Marmora the junction depth of the salt and fresh water is about seventy. A boat trimmed with about two hundred pounds of negative buoyancy out there will, if she stops her motors, sink slowly through the upper layer of fresh (or brackish) water, till she meets the denser salt below; on reaching this she will be in a state of "positive" buoyancy, and after a little bouncing up and down to find her "zero" stratum, she will settle at a steady depth. The same sort of thing—a blessing in the Marmora—is a nuisance in the Bight. A boat crossing the mouths of the German rivers may be at one moment diving comfortably with zero helm on the hydroplanes—the next, she meets a layer of fresh water from the Jahde ebb and is bumping on the bottom with "hard-up" helm and the pumps working on the tanks.
II
The exploits of "E 11" in the Dardanelles have been published during the war; this boat, however, did not begin her war career in the Sea of Marmora—she had already shown her usual attitude of contemptuous familiarity towards the enemy when on patrol in the Heligoland Bight. On one occasion in 1914 she certainly met a "ghost"—i.e., something which never gave any satisfactory explanation of what it was. "E 11" was diving in sight of Heligoland, and having sighted a line of four destroyers coming over her horizon, she turned in to attack them. Suddenly her bow was jerked up to a startling angle, and tanks had to be hastily flooded to prevent a "break surface." The boat then seemed to go crazy—taking angles by the bow or stern apparently in defiance of all laws of hydrostatics. The captain made up her mind for her by running her down to the bottom in 65 feet and holding her there. In a few minutes the sound of screws came from overhead, and the same sound continued for several minutes. "E 11" was then dived up off the bottom, but was found to be still in the same strange condition, taking up this time an angle of 20 degrees up by the bow. She was once more taken down and held to the bottom, while again screws passed by and curious noises came from overhead. The noises went on for an hour, during which time the officers and crew—with the business-like decision of the British nation—had tea. When the noises had stopped "E 11" was again lifted, when she showed a perfect trim and instant obedience to her hydroplanes, proceeding along at her normal patrol depth as if she had never given any trouble at all. Nothing was in sight through the periscope except Heligoland, and the explanation of "E 11's" hysteria is still her own secret.
The same boat, as was reported at the time, shared a Christmas dinner with some representatives of the R.N.A.S. on the day of the 1914 Cuxhaven air raid. The Germans have not given us their version of what happened, but from the following it will be seen that it is a pity that they did not publish an uncensored story.
At 11 A.M. "E 11" was diving on her billet to the westward of Norderney, when she saw through the periscope a seaplane coming out to seaward and flying low. She came to the surface, and, having been placed on that billet "according to plan," was not surprised to find that the machine was British. The seaplane took the water safely, and "E 11" took her in tow with the idea of saving the machine. The pilot (carrying his confidential bomb-sight with him) was taken on board first. Hardly had the tow started when two more seaplanes were seen approaching from the direction of the shore, one of them flying very groggily and looking like an imitation of a tumbler pigeon. "E 11" stopped and the machines closed her; so did a large Schutte-Lanz type airship, which was presumably in pursuit of them. Of the two seaplanes the undamaged one came down comfortably close to the submarine, and then all spectators stood up to watch the alighting of the other, which was seen to have had its tail shot off and to be under the nominal control of its ailerons only. Everybody held their breath as the pilot brought the machine down, and there was a general groan of sympathy as the crash came. She pitched nose first into the sea, and it looked as though the pilot could hardly have survived; then a wet figure was seen to climb slowly out of the wreck and perch cross-legged on the tip of the broken tail. By this time the enemy airship had arrived, and "E 11" realised that speed in picking up the seaplane pilots was becoming more advisable every minute. An additional complication chose this moment to turn up in the shape of a U-boat,[ [3] which appeared on the surface about two miles away and then dived—presumably to attack with torpedoes. "E 11" at this stage of the war was unfortunately not fitted with a gun. She slipped tow from Number One seaplane and fired several revolver bullets through its floats to ensure its sinking. She then closed Number Two and took the pilot and observer off her just as the airship arrived overhead at a height of two hundred feet. The faces of the Germans in the gondolas could be clearly seen, and the men in the middle car were displaying considerable activity—probably wrestling with a faulty bomb-dropping gear. Before the bombing business was in working order, however, the light breeze had carried the airship down to leeward—much to the relief of "E 11," who saw the enemy restart her engines in order to make a sweep round and get into position again. "E 11" having punctured the floats of Number Two seaplane with bullets, manœuvred alongside Number Three, and picked up a very wet pilot and mechanic. By this time there was every probability of the U-boat having approached inside easy torpedo range—in fact "E 11" was wondering why the expected torpedoes were so slow in arriving. For this reason, and also because the airship was now nearly back overhead again, any further delay was rash, and so the pilot and mechanic were unceremoniously hustled below, and "E 11" demonstrated to them what a "crash-dive" was like from inside. The depth gauges had just reached nineteen feet when two heavy explosions occurred on the surface,—the enemy's bomb-dropping gear was working nicely again, but too late. "E 11" went under feeling a little hurt at having had to leave a job unfinished; she had meant to sink Number Three seaplane before leaving, and was unhappy at the idea of it being still of use to the enemy. On rising sufficiently to use her periscope, however, she was delighted to observe the Schutte-Lanz venting its hate in machine-gun fire on the abandoned machine—an expenditure of ammunition which continued until the sorely-tried raider sank. "E 11" was for a moment inclined to come up to pass a polite signal of thanks to the enemy, but, after consultation, it was decided that humour was wasted on Germans, and so the boat was taken on to the bottom for a rest while the Xmas dinner was disposed of. The five passengers shared the dinner, and presumably enjoyed the day, but it blew half a gale and more all the way home to Harwich, and the motion of an "E" boat takes a lot of getting used to.
Everybody has read of the doings of this submarine in the Sea of Marmora, and I will try to avoid writing about despatches already published; but I think the actions between submarines and soldiers have been perhaps only lightly touched on, in view of the fact that such actions are so unique in their nature and circumstances.