The feelings of the average landsman, when he sets foot for the first time in a submarine, are a strong mixture of curiosity and apprehension. The curiosity is uppermost—the experience before you is much more novel than, for example, that of a first trip in an aeroplane. From a mountain or tower, a great wheel or a balloon, you have seen the bird’s-eye view of the earth and felt the sensation of hanging over the aerial abyss. But even the fascinating pages of Jules Verne have not told you all that you will feel in a submarine, and nothing but physical experience can do so. You are eager to see the working of new mechanical devices in a wholly strange element, and to learn the use of a new weapon in a wholly strange kind of war. But with this eagerness, there is an underlying sense of uneasiness, a feeling that you are putting yourself into a position where you are as helpless as a mouse in a patent trap. The cause of this is not fear of war risks, for it is equally strong in harbour, or in time of peace. It is probably connected with the common dread of suffocation, which may be an instinct inherited from ages of primitive life in the open. They will tell you, in the submarine service, that it is a mere habit of mind and very soon forgotten. There is even a story of an officer who, on coming ashore from a year’s work in an E-boat, refused to travel in the Tube railway, because it looked so dangerous. He preferred the risks he was used to, and so do most of us.

You stand, then, at the foot of the narrow iron ladder down which you have come from the upper air, you gag your inherited instinct, and let your curiosity loose. Before the boat dives, there is time for a good deal to be taken in. The interior seems large beyond expectation. This is partly an illusion, produced by the vista of the compartments, fore and aft of the central control where you are standing. The bulkhead doors being all open at this moment, you can see into the engine and motor rooms towards the stern, and forward through the battery compartment to the bow torpedo-tubes. The number of men seems large too, and they are all busy; but you note that every part of them is more active than their feet—there is very little coming and going. In the control, close to you, are the captain, a lieutenant, a steersman, and seven or eight other men for working the ballast tanks, air valves, electrical apparatus, and hydroplanes. The last two of them have just come down from the deck—the hatches are closed—engines have already been running for some minutes, though the order escaped your observation.

You are invited ‘to see her dive.’ You go up to the forward conning-tower scuttle and flatten your face against the thick glass. An order is given. You hear the hissing of air, as the ballast tanks are filled. You expect to see the forward part of the boat dip down into the water in which she is heaving. Instead of that, it is apparently the sea which lifts itself up, moves along the deck, and seems to be coming in a huge slow wave over your scuttle. The light of day gives place to a green twilight, full of small bubbles. Mentally you feel a slight chill; but physically, a warm and sticky sensation. As there is nothing more to be seen out of window, you return to your instructor. He explains to you that the ship is now running on her motors, and that her speed is therefore low—not nearly enough to overhaul a vessel or convoy of any power. On the surface, with her other engines, she could far more than double the pace; and even with the motors, she could do a spurt for a short time—but spurts are very expensive; for they use up the battery power with ruinous rapidity, and then a return to the surface will be necessary, whether safe or not.

At this point it may strike you suddenly that you are now under water—you begin to wonder how deep you are, and why you have not perceived any change in the boat’s position. The answer is that the depth marked on the gauges is only twenty feet, and the angle of descent was therefore very slight—much too slight to be perceptible in the short length of a single compartment. The depth of twenty feet is now being maintained with surprising steadiness; the explanation is that two entirely separate forces are at work. First, there are the horizontal rudders or hydroplanes, fitted outside the vessel both fore and aft, by which she can be forced down, provided she has sufficient way on, in much the same fashion as an ordinary vertical rudder forces a ship to one side or the other. But this is only the diving apparatus; to keep her down, there is her water ballast—the water which was taken into her main ballast tanks, when the order to submerge was given. These tanks contain a sufficient weight of water to counteract the normal buoyancy of the boat, by which she would naturally float upon the surface. When they are emptied, she will neither sink nor rise of her own motion—she will lie or run at whatever depth she is placed, by her hydroplanes or otherwise.

These, you will have noticed, were called the ‘main’ ballast tanks—there would seem then to be others. There are, and several kinds of them. First, there is an auxiliary ballast tank, which has a peculiar use of its own. A submarine must be able to float or submerge in fresh water as well as at sea; for her base or harbour will often be in the mouth of a river, or she may have to navigate a river, a canal, or a lake. It is a point that would not probably have occurred to you, but the difference between the density of fresh and salt water is sufficiently great to make a real difficulty here. Everyone knows that it is less easy to float in fresh water, and less easy to sink in salt. For practical purposes, a submerged boat is less buoyant in fresh water by 26 tons in 1000, and vice versa; so that when a submarine of 1000 tons leaves a river for the sea, she must take an extra 26 tons of ballast to keep her down, and when she comes home again she must get rid of 26 tons, or she will sink so much deeper in the fresh water. For this purpose she has a special tank of the right size, proportioned to her tonnage; and it is placed in the middle of the ship, in order that it may not interfere with her trim when it is filled or emptied.

That last remark will put you in mind that, in any kind of navigation, the trim of the boat is a delicate and important matter. Even in very large and heavy ships you may be able, by shifting guns or cargo, to slip off a shoal, or right a leaking vessel after a collision. In a tickle boat like a submarine, it is necessary to have some means of trimming the vessel, fore or aft, at any moment, and especially when about to dive, or when caught by some under-water obstruction. Tanks are therefore fitted for this purpose at each end of the boat. They are comparatively small, because the effect required is in ordinary circumstances very limited, and in a desperate emergency they may need to be supplemented by rushing the crew fore or aft, as living ballast. An example of this will be found in a later chapter.

You may now feel that you have heard enough of tanks; but your instructor will insist on showing you a whole additional series. He will make a point of your recognising that a submarine, when submerged, is in reality hanging in the water as a balloon hangs in the air, and for every loss of weight she must be instantaneously compensated, or she will begin to rise. What loss of weight can she suffer while actually under water? It is not perhaps very hard to guess. There is, first of all, the consumption of oil by the engines; secondly, the consumption of food and fresh water by the crew; and thirdly, the departure from time to time of torpedoes. Also, when on the surface, there may be gun ammunition fired away, or other things heaved overboard, and allowance must be made for this when the boat goes down again. The modern submarine is prepared to keep her balance under all such circumstances. She has compensating tanks, and they are placed as near as possible to the oil-tank, fresh-water tank, or torpedo-tube, for whose diminished weight they are to compensate.

You are probably more interested in the torpedo-tubes than in the oil-tanks. It is time then to go forward. You pass through the battery compartment, where the officers’ quarters are, and are shown (under the floor) the accumulators, ranged like the honey sections in the frames of a beehive, and very carefully covered over with flexible waterproof covering as well as with close-jointed planking. What would happen if water did find its way down to the batteries? An instant discharge of chlorine gas, blinding and suffocating. What would you do then? Come to the surface at all costs—and lucky if you are in time! The Germans know all about that—and not long ago one of our own boats was only saved by the good goal-keeping of a lieutenant, who caught up a lid of some sort, and stood by the leak, neatly fending off the water spurt from the door of the battery compartment.

Now you are in the forward torpedo compartment, and there are the tubes. I need not say anything about their size or number—you will realise at a glance that when a couple are loosed off at once, a good deal of weight goes out of the ship. The ordinary 18-inch fish is 17 feet long, and takes some handling. The explosive alone in her war-head weighs as much as a big man, say 12½ stone, and a 21-inch fish carries twice as much as that, packed in some four feet of her length. Behind that comes the air chamber—another ten feet—with the compressed air to drive the engine, which is in her stern. The air is stored at a pressure of over 2000 lbs. to the square inch; so the steel walls of the chamber must be thick, and this makes another heavy item. Lastly, there is the engine-box with its four-cylinder engine, two propellers, gyroscope and steering gear. Altogether, an 18-inch fish will weigh nearly three-quarters of a ton, and a 21-inch over 2000 lbs., so that the amount of compensation needed when you fire, is considerable.

To see how it is done, we will imagine ourselves firing this starboard tube. The torpedo is got ready, and special care is taken to make sure that the firing-pin in her nose is not forgotten. Cases have been known in which a ship has been hit full by a torpedo which did not explode—just as a good many Zeppelin bombs were found in London, after the early raids, with the detonating pin not drawn. The fish is now ready to come alive, and is slid into the tube. The door is shut behind it, and the water-tight outer door, at the other end of the tube, is now ready to be opened by powerful levers. But the immediate result of this opening would be an inrush of sea-water which would weigh the boat’s head down; for though the fish’s belly fits the tube pretty closely, there is a good deal of empty space where it tapers towards the nose and tail. Here comes in the tank system. When the tube is loaded, this empty space is filled by water from within the ship, so that no change of weight occurs when you open the outer door. But when the firing-button has been pushed, and the torpedo has been shot out by an air-charge behind it there is no possibility of preventing the whole tube from filling with water, and this water must be got rid of before the tube can be reloaded. To do this, you first close the outer door again; then you have to deal with the tubeful of water. A good part of it is what the ship herself supplied to fill the space round the torpedo; and this must be pumped back into the special tank it came from. The remainder is the sea-water which rushed in, to take the place left empty by the departing torpedo: and this must be pumped into another special tank to prevent the ship feeling the loss of the torpedo’s weight. When you get a fresh supply of torpedoes, these special compensating tanks (which are really a kind of dummy torpedoes) will be emptied out, one for each new torpedo. Meantime, you have now got the tube empty, and can open the inner door and reload.

But what of the torpedo which has been fired? It is travelling towards its mark at a speed of between thirty-five and forty knots, if we suppose the range to be an ordinary one, under 1000 yards, and the torpedo to have been ‘run hot,’ i.e. driven by hot air instead of cold. The compressed air is heated mechanically inside the torpedo, in the act of passing from the air chamber to the machinery, and this increases both the speed and range. But it is not always convenient or possible to start the heating apparatus, and even when ‘run cold’ the fish will do thirty knots. This speed is amazing, but it is one of the least wonderful of the torpedo’s qualities. The steering of the machine is a double miracle. One device makes it take, after the first plunge, exactly the depth you desire, and another—a gyroscope fitted inside the rudder gear—keeps it straight on its course; or makes it, if you wish, turn in a circle and strike its prey, boomerang fashion. The head of the fish can also be fitted with cutters which will cut through any torpedo-netting that a ship can afford to carry. The only thing that no ingenuity can accomplish is to make a torpedo invisible during its run. The compressed air, when it has passed through the engine, must escape, and it comes to the surface in a continuous boiling line of bubbles. This is visible at a considerable distance; and though, when the track is sighted by the look-out, the torpedo itself is of course always well ahead of the nearest spot where the bubbles are seen rising, it is surprising how often ships do succeed in avoiding a direct shot. A prompt cry from the look-out, a steersman ready to put his helm over instantly, and the torpedo goes bubbling past, a few feet ahead or astern, or comes in on a tangent and runs harmlessly along the ship’s side without exploding. Then away it goes across the open sea, until the compressed air is exhausted, the engine stops, and the mechanical sinker sends it to the ocean bed, which must be fairly strewn with dead torpedoes by this time; for as we know, to our advantage, the proportion of misses to hits is very large in the U-boat’s record.

Now that you have seen the weapon—and can at any rate imagine the handling of it—you are naturally keen to sight the game, and realise the conditions of a good shot. You go back to the central compartment, where the Commander is ready to show you a ship through the periscope. Not, of course, an enemy ship—in this war, if you want a shot at an enemy ship, you must go into his own waters—into the Bight or the Baltic—to find him; and even there he is probably tucked up very tight in his berth, with chained barges and heavy nets all round him, and mines all up the approach. But there are plenty of our own ships out every day—sweeping, cruising, trading; and transporting men, food, mails, and munitions. And what you see will help you to understand why the Germans have spent so many torpedoes, and sunk so comparatively small a proportion of our enormous tonnage.

The boat is now less deep in the water; the gauges mark 15 feet, and you are told that the top of the periscope is therefore some two feet above the surface. The shaft of it is round, like a large vertical piston; but at the bottom it ends in a flattened box, with a hand-grip projecting on each side. You take hold of the grips and look into the box. Nothing is visible but an expanse of water, with a coast-line of low hills beyond it—all in miniature. The Commander presses the back of your left hand on the grip, and you move round slowly as the periscope revolves. The coast-line goes out of the picture, the sea lies open to the horizon, and upon it appears a line of odd-looking spots. They are moving; for the nearest one, which was narrow a moment ago, is now three or four times as broad, and is in a different place in the line.

The line, you are told, is not a line at all, but a convoy, in fairly regular formation. The nearest spot is a destroyer, zigzagging on the flank; the others are ships which have been so effectively ‘dazzled’ that their shapes are unrecognisable. You carry on, in hope of something nearer, and suddenly a much larger object comes into the field of vision. A ship, of course, though it does not look like any ship you have ever seen; and you are asked to guess its distance and direction. You are bewildered at first; for as you were moving the lens rapidly to starboard, the vessel came in rapidly to port, and as her dazzle-paint makes her stern indistinguishable from her bows, you continue to think she is steaming in that direction. After a more careful observation, this mistake is corrected. She is crossing us from port to starboard. But at what angle? This is vitally important, for the possibility of getting in a successful shot would depend entirely upon the answer. We are ourselves heading about due north: she is crossing to the east: if her course is south of east, she is coming nearer to us, and our torpedo would strike her before the beam—the most favourable chance. If, on the contrary, her course is north of east she is going away, and the torpedo would have a poor chance of hitting her abaft the beam. In fact, it would not be worth while to risk losing so costly a shot. A torpedo at present prices is worth not far short of £2000, and we only carry two for each tube.

You look long and hard at this dazzle-ship. She doesn’t give you any sensation of being dazzled; but she is, in some queer way, all wrong—her proportions are wrong, she is somehow not herself, not what she ought to be. If you fix your attention on one end of her, she seems to point one way—if you look away at her other end, she is doing something different. You can’t see the height of her funnels clearly, or their relative position. But, with care, you decide that she is coming about south-east and will be therefore your bird in two minutes’ time. The Commander is interested. He takes a look himself, laughs, and puts you back at the eye-piece. You hold on in hope that he may, after all, be wrong; but the bird ends by getting well away to the north-east. Your error covered just ninety degrees, and the camouflage had beaten you completely. You begin to think that the ingenuity at command of the nation has been underestimated. But this ship is nothing of a dazzle, the Commander tells you—he can show you one whose cut-water seems always to be moving at a right angle to her stern!

He adds that he knew all about that cruiser, and she knew all about him. Otherwise he would not have shown even his periscope; and if he had, she would have had a shell into him by now, and a depth-charge to follow. A depth-charge is perhaps the most formidable weapon against which the submarine has to be on guard. It is a bomb, with a detonator which can be set to explode when it reaches any given depth. A small one would need to hit the mark full, or be very close to it, in order to get a satisfactory result; but the newer and larger ones will seriously damage a submarine within an area of forty yards. The charge is either dropped over the stern of the pursuing vessel, when she is thought to be just over or just ahead of the enemy; or it is fired out of a small and handy short-range howitzer—a kind of lob-shot, a number of which can be made by several patrol boats acting together, so as to cover a larger area with much less risk of embarrassing each other. Even if the submarine is not destroyed outright, the chances are in such a case that she will be so damaged as to be forced to the surface or to the bottom, and then the end is certain. A bad leak would bring her up—an injury to her tanks or rudders might drive her down.

You are uncomfortably reminded once more of that inherited dislike of death by suffocation. If a submarine cannot rise to the surface, you ask, is there no possible means of escape? The answer is that it may be possible, with great difficulty, to get out of the boat; but there is very little chance that you would survive. The lungs are not fitted to bear so great and sudden a change of pressure as that felt in passing from the boat to the water, and from the deep water to the surface. You are perhaps surprised; but the pressure of sea-water at 160 feet is equal to five atmospheres, or about 75 lbs. to the square inch. To pass safely through this to the ordinary surface atmosphere would need a long and gradual process, and not a sudden rise of a few seconds. A very brave attempt was made on one occasion, when a British submarine had gone to the bottom during her trials, and could not be got up by any effort of her crew. The agony of the situation was intensified by the fact that help was close at hand, if only the alarm could be given, and the whereabouts of the submarine communicated to the rescuers. The officers of the sunken boat were, of course, perfectly aware of the danger from sudden change of pressure; but one of them volunteered to go to the surface, alive or dead, and carry a message on the chance of attracting some ship’s attention. To lessen the risk as far as possible, it was arranged that he should go up into the conning-tower, and that the hatch should then be closed beneath him and the water gradually admitted. As it flowed slowly in, and mounted round him, the air in the top of the conning-tower would diminish in extent but increase in pressure. When it reached his neck, the internal pressure would be nearly equal to the external. He would be able to open the top, possibly to make his escape, and conceivably to reach the surface without his lungs being fatally injured. If he failed, he would at any rate have given his life for the chance of saving his comrades.

The Commander accompanied him into the conning-tower, meaning, it is said, to return into the ship himself when he had seen to all the arrangements. But when the water was admitted, the two of them were shot out together, and as it happened it was the volunteer who was killed, by striking against the superstructure, while the Commander came up alive. In no long time—though it must have seemed unendurably long to those below, waiting in complete uncertainty—the rescuers were informed, found the submarine, and got a hawser under her stern. They raised her high enough out of the water, vertically, to open a hatch and save the crew. Then the hawser gave, and the boat went down again.

That story is not unlikely to haunt you all the way home, and for a long time afterwards. It may even make a difference to your whole feeling about the war under water, as waged by our own Service. The submarine is not merely an incredibly clever box of mechanical toys, nor is it only the fit weapon of a cruel and ruthless enemy; it is also a true part of the Navy without fear and without reproach, whose men play the great game for each other and for their country, and play it more greatly than we know. The tune of their service is a kind of undertone; but it is in the heroic key, and cannot fall below it.