IN 1916 we began to look to Germany to produce something very unpleasant in the way of submarines. We were certain she would follow the obvious course indicated by the lessons all belligerents were learning, and produce the big U-oruiser. Very fortunately for us, she produced nothing of the sort until well into 1918, when one small U-cruiser did us a great deal of damage. The point was this-We were worrying and chasing U-boats with trawlers, motor-boats, destroyers, and numbers of other comparatively small and weakly-armed craft. If a U-oruiser, armed with, say, four 6-inch guns, and armoured along her topstrakes, had risen to fight her tormentors-well, it is clear that our small patrol-vessel service would have become suddenly very expensive. Each convoy would have required cruiser protection, and we had not enough cruisers to provide this. In 1917, by our constructor's reckonings, there was no reason why a German submarine could not have been produced which could proceed safely to the East Indies (round the Cape), and repeat (on a bigger scale) the exploits of the Emden. Well, the Germans didn't do it; they produced U-cruisers with

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two 59 guns apiece in 1918, but the type was unsatisfactory and unstable. It is still a puzzle to us that the idea came to them so slowly. We had K-class boats with the fleet in 1916 of 2600 tons, and had shown that a big submarine was a working proposition. (The K-boat, of course, is not a cruiser-submarine; she is a fast and lightlygunned type for use in battle only, and she does not leave the fleet except when detached for watching patrols.) We produced the M-class in 1917, and-for obvious reasons-we kept the type as secret as possible until the Armistice. The M-boat is rather smaller than the K, and is of only seventeen knots speed, but she has far better under-water capabilities than her big companion. She carries, besides her torpedo armament, 12-inch gun of the normal battleship type. This gun can be carried loaded submerged by the use of a watertight tampion and breech. The boat can rise in the wake of an enemy, fire as she "breaks surface," and submerge again

all in a matter of seconds.

The type was extremely successful, and one can only be thankful that such boats were not on the enemy's side. They would have been the very devil

to deal with on the trade routes, and would have caused us to reconsider very hurriedly our whole system of anti-submarine defence. Of course, four 6inch would be better than one 12-inch from a German point of view, especially as a destroyer would be likely to attack unscathed under the fire of one big gun, but our type was intended for use against such things as enemy cruisers, and not for sinking merchant ships. By the end of the war the enemy had arrived at the stage of submarine design where one says, "We've got a type that works -let us stick to it, and just add improvements." We passed that stage before the war and are now in the confident (with reservations!) state of feeling that we can turn out anything required to combine the properties of under-water and surface oraft. If submarines continue as weapons of war, they will improve very considerably, and the range of possibility of future types is so great that any prophecy now would be rash. It must be remembered, however, that the depth of water in which a boat is intended to operate limits her size. It is not only that the distance from her keel to periscope is (in the case of a big boat) some 50 feet, but also that the great length of a big boat's hull means that even a slight fore-and-aft inclination as she dives will add enormously to her draught; a very long boat in twenty fathoms of water (the North Sea average) would have to be careful not

to get off an even keel, as it might happen that in the presence of the enemy her bow or stern would touch bottom, with the result of causing the whole boat to bounce up to the surface. A submarine submerged is in a state of equilibrium, in that she has little or no tendency to rise or sink if her motors are stopped and the boat left to herself. I am afraid in this history that I continue to speak of submarines as if everybody knew a good deal about them. I use technical expressions and words as if I was dealing with things like motor - oars, I will try and explain more clearly what I mean by "bouncing to the surface," and will do so in the idea that there are probably readers who know as much about diving boats as I do of bimetallism.

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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 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 convenienoe 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, &c. 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 depthline 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 water-tight, 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

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she goes down; until the vents 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 halfsubmerged; 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 occurrence, if too rough a "landing" is made, to proceed like a tennis - ball along the

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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 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,

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 hydro

planes, 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 SchutteLanz type airship, which was presumably in pursuit of them, Of the two seaplanes the un

damaged 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 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, 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 the 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-prebably wrestling with a faulty bomb-dropping gear.