CHAPTER XIII

GETTING THE BEST OF THE U-BOAT

The U-boat commander who sallied forth from the harbor of Wilhelmshaven in the early days of the war had nothing to fear. He was out to murder, not to fight. His prey was always out in the open, while he could kill without exposing more than his eye above water. Not even a sporting chance was allowed his victims, particularly when he chose unarmed merchantmen for his targets. He could come up boldly to the surface and shell a ship into submission. This was cheaper than torpedoing the vessel, because torpedoes are expensive. If the ship were speedy it might run away; or if the U-boat came up too close to its intended prey, the latter might run it down. That happened occasionally and it was the only danger that the _Herr Kommandant_ had to fear.

If a destroyer suddenly appeared, the U-boat could dive into the shelter of the sea. If the water were not too deep, it could lie on the bottom for two or more days if need be. There was plenty of air in the hull to sustain life for many hours, and then the compressed air used for blowing the ballast-tanks could be drawn upon. In the U-boat there were potash cartridges to take up the carbon-dioxide, and tanks of pure oxygen to revitalize the air. If the submarine were damaged, it was not necessary for it to come to the surface to effect repairs. There were air-locks through which a diver could be let out of the boat. He was fitted with oxygen and potash cartridges, so that he did not need to be connected by an air-hose with the boat, but could walk around it freely to mend injured rudders or to clear the propeller of entanglements.

Even the small submarines of those early days were capable of taking long voyages. Setting his course at a comfortable pace of 10 knots, the U-boat commander could count on enough fuel to carry him 1600 miles, and if need be he could slow down to 8 knots and by using certain of his water-ballast tanks for additional oil-reservoirs, extend his cruising-radius to nearly 3000 miles. The big 800-ton U-boats that were built later had a radius of 5000 miles at an 8-knot speed. And so when the British closed the English Channel with nets and mines, _Herr Kommandant_ was not at all perturbed; he could sail around the British Isles if he chose and make war upon transatlantic shipping. When harbors were walled off with nets, he could remain outside and sink vessels that were leaving or entering them.

SUBMARINE-CHASERS

A real menace came when the U-boat commander popped his periscope out of the sea and saw several little motor-boats bearing down upon him. They seemed harmless enough, but a moment's inspection showed them to be armed with guns fully as powerful as those he carried. It was useless to discharge a torpedo at so speedy and small a foe. A torpedo has to have a fairly deep covering of water, else its course will be disturbed by surface waves; and the submarine-chasers drew so little water that a torpedo would pass harmlessly under them. It was useless for the U-boat commander to come up and fight them with his guns. They would have been upon him before he could do that, and their speed and diminutive size made them very difficult targets to hit. Besides, he dared not risk a duel of shell, for he knew that if the precious inner hull of his boat were punctured, he could not seek refuge under water; and if he could not hide, he was lost. The little armed mosquito craft swarmed about the harbor entrances, ready to dash at any submarine that showed itself. They could travel twice as fast as the submarine when it was submerged and half again as fast as when it was running on the surface.

Submarines had to take to cover when these chasers were about. _Herr Kommandant_ did not even dare to take a look around through his periscope, because the streak of foam that trailed in its wake would betray him and immediately the speedy motor-boats would take up the chase; and they had a disagreeable way of dropping bombs which, even if they did not sink the submarine, might produce such a concussion as to spring its seams. His foes had discovered one of his most serious defects. He was blind under-water and they were making the most of this handicap.

Groping along under-water by dead-reckoning was not any too safe a procedure near land, because he was liable at any moment to crash into an uncharted rock or maybe into the wreck of some submarine victim. He could not correct his bearings without coming to the surface, and, in the black depths of the sea, a slight miscalculation might send him to his doom. As was explained in the previous chapter, he had to keep moving, because he could not remain suspended under water.

He was more helpless than a ship sailing in the densest of fogs. A ship can stop and listen to sound-signals, or even to the beating of the surf on the shore, or it can take soundings to locate its position; and yet it is no uncommon occurrence for a ship to run ashore in a fog. How much easier it is for a submarine to lose its bearings when obliged to travel by dead-reckoning, particularly in the disconcerting excitement of the chase! To avoid the danger of collision with surface vessels, the commander chose to run at a depth of sixty-five feet. That was the upper limit of his safety-zone. A depth of over two hundred feet was his lower limit, because, as stated before, the water-pressure at that depth would crush in his hull or at least start its seams. If the bottom were smooth and sandy, and not too deep, he could settle gently upon it and wait for darkness, to make his escape.

But while he lay on a sandy bottom, he was still in danger. Trawlers were sweeping the bottom with nets. He might be discovered; and then if he did not come up and surrender, a bomb would let in the sea upon him.

A HINT FROM NATURE

While he could not see under water, his adversaries could. They had taken a hint from nature. The fish-hawk has no difficulty in spying his submarine prey. Flying high above the water, he can see his victims at a considerable depth, and wait his chance to pounce upon an unwary fish that comes too near the surface. It is said that the British trained sea-gulls to hunt submarines. Sea-gulls will follow a ship far out to sea for the sake of feeding on refuse that is thrown overboard. British submarines encouraged the birds to follow them, by throwing out bait whenever they came to the surface. Of course the birds could see the submarine even when it was submerged, and if they pursued it, they were always rewarded with plenty of food. The gulls drew no fine distinction between Hun and Briton, and so it came that _Herr Kommandant_ often groped his way along in the dark sea, totally oblivious of the fact that he was attended by an escort of feathered folk who kept the British chasers informed of his presence.

In this connection it is interesting to note that the British trained sea lions to hunt submarines. The animals were taught at first to swim to a friendly submarine, locating it by the sound of its propellers. They were always rewarded with fish. These sea lions were muzzled so that they could not go fishing on their own account. Then they learned to locate enemy submarines and pointed them out by swimming directly toward them and diving down to them.

But there were human eyes, as well, that spied upon the U-boat. Fast seaplanes patrolled the waters, searching constantly for any trace of submarine. Its form could be vaguely outlined to a depth of from fifty to seventy-five feet, unless the sea were choppy, and once it was discovered, chasers or trawlers were signaled to destroy it with bombs or to entangle it in nets. Often a submarine would be discovered by a leak in its oil-tank which would leave a tell-tale trail. Sometimes when the U-boat itself could not be discerned, there would be slight shimmer, such as may be seen above a hot stove, caused by refraction of light in its wake. This was easily recognized by trained observers.

Even better aërial patrols were the small dirigibles known as Blimps. They are a cross between a balloon and an airplane, for they have the body and the power-plant of an airplane, but the planes are replaced by a gas-bag. Blimps could cruise leisurely and search the sea thoroughly. They could stop and hover directly over a submarine and drop explosives upon it with great accuracy. And so _Herr Kommandant_ could take no comfort in hiding under a blanket of waves unless the blanket were so thick as to conceal his form completely from the eyes overhead. This made it imperative to leave the shallower waters near shore and push out into the deep sea, where the small chasers could not pursue him. But he could not shake off his pursuers. Stream-trawlers are built to ride the heaviest gales and they took up the chase out into the ocean.

There was a decided advantage for the U-boat in moving out to sea. It had a wider field of activity and could more easily escape from its pursuers. But on the other hand, its prey also had an advantage. Out in the open ocean they were not obliged to follow the usual ship lanes and it was more difficult for a submarine to intercept them. There it took more U-boats to blockade a given area.

A GAME OF HIDE-AND-SEEK

Then, it ceased to be quite so one-sided a game when merchantmen began to carry guns. That made it necessary for the submarine commander to creep up on his victims stealthily, and depend upon his torpedoes. He had to get within a thousand yards of the ship and preferably within five hundred yards, in order to be sure of hitting it. If the ship could travel faster than he could, he had to do this without betraying his presence. But ship-captains soon learned that their safety lay in zig-zagging. When _Herr Kommandant_ reached the point from which he had planned to attack, he would raise his telescopic periscope out of the water, expecting to see his victim within good torpedo range, only to find it sailing safely on another tack. Again, he would have to take observations and make another try, probably with no better luck. It was a game of hide-and-seek in which the merchant ship had a good chance of making its escape, particularly when blotches of camouflage paint made it difficult for him to get the range, as described in Chapter XI.

Slower ships could be attacked without all this manoeuvering, provided the submarine's guns outranged those of the ship. And so U-boats were provided with larger and larger guns, which made it possible for them to stand off and pound the merchantmen while out of reach of the vessel's guns. But ships found a way of hiding on the surface of the sea. A vessel would spout forth volumes of dense black smoke which would obliterate it from view. (See Fig. 19.) If the wind was quartering, the ship would change its course and dodge behind the sheltering pall of smoke. Not only was the smoke produced on the vessel itself, but smoke-boxes were cast overboard to form a screen behind the vessel. These smoke-boxes contained a mixture of coal-tar and phosphorus and other chemicals which would produce incomplete combustion. They were ignited by the rubbing of a phosphorus compound on a priming-composition, and then cast adrift to pour out dense volumes of heavy smoke. (See Fig. 20.) Behind this screen, the ship could dodge and zig-zag and if her speed were greater than that of the submarine, her chances of escape were very good.

Another annoyance that _Herr Kommandant_ experienced was, when he lifted his periscopic eye above water, to find it so smeared with a sticky substance that he could not see. His foes had strewn the water with tar-oil that had spread in a thin film over a surface miles in extent. This blinded him at first, but before long he was equipped with a jet for washing off the periscope glass and that little annoyance was overcome.

But the craft most dreaded by the U-boat commander were the destroyers. These light, high-powered, heavily armed vessels could travel twice as fast as he could on the surface and three times as fast as he could submerged. Shells were invented which would not ricochet from the surface of the sea, but would plow right through the water, where they struck and hit the submarine below water-level.

DEATH-DEALING "ASH CANS"

However, it was not shell-fire that he dreaded, but the big "ash cans" loaded with TNT which were timed to explode far under water, and which would crush his boat or start its seams. It was not necessary for these bombs to hit the U-boat. When they went off they would send out a wave of pressure that would crush the boat or start its seams even if it were a hundred feet and more from the point of the explosion. Within limits, the deeper the explosion the wider would its destructive area be.

The timing-mechanism of some depth bombs consisted merely of a float on the end of a cord. When the bomb was thrown overboard this float remained on the surface until the cord was pulled out to its full length, when there would be a yank on the firing-trigger and the charge would explode. In other depth bombs there was a valve operated by the pressure of the water. When the bomb sank to the depth for which the valve was set, the pressure of the water would force the valve in, exploding a cartridge which set off the charge. So powerful were these depth bombs that the destroyer had to travel at high speed to get out of range of the explosion.

Depth bombs were rolled off the stern of the destroyer and also thrown out from the sides of the vessel by means of mortars. Some of the mortars were Y-shaped and held a depth bomb in each arm of the Y. When a blank 3-inch shell was exploded at the base of the gun, both bombs would be hurled from the ship, one to port and the other to starboard. In this way the destroyer could drop the bombs in a "pattern" of wide area. _Herr Kommandant_ gained a wholesome respect for these terriers of the sea. It was suicide to show himself anywhere near a destroyer. In a moment the speedy boat would be upon him, sowing depth bombs along his course. His chances of escaping through this hail of high explosives were remote indeed.

The ships that he was most eager to destroy were either too speedy for him to catch, unless they happened to come his way, or else they were herded in large convoys protected by these dreaded destroyers. The convoy proved a most baffling problem for _Herr Kommandant_. He dared not attack the convoy by daylight. In a fog he might take a chance at picking off one of the ships, but even that was very risky. He could trail the convoy until dusk and then under cover of darkness draw near enough to discharge a torpedo, but in the daytime he must keep his distance because there were eyes in the sky watching for him. At the van and rear of the convoy there were kite balloons high in the sky, with observers constantly watching for periscopes, and for U-boats that might be lurking under the surface.

As the destroyers gained in experience, the difficulties of the U-boat attack grew greater and its work grew more and more perilous. The crew grumbled and grew mutinous. The morale of the men was shaken. We can imagine the horror of plunging hurriedly into the depths of the sea, and rushing along blindly under the surface, dodging this way and that, while terrific explosions of depth bombs stagger the submarine and threaten to crush it, and there is the constant expectation that the next explosion will tear the thin shell of the U-boat and let in the black hungry water. The tables were turned. Now, if never before, _Herr Kommandant_, the hunter, knew what it felt like to be hunted.

It takes an exceptional man to go through such a harrowing experience with unshattered nerves. On at least one occasion, a submarine that was being depth-bombed came suddenly to the surface. The hatch flew open and the crew rushed out, holding up their hands and crying, "_Kamerad_." The U-boat was uninjured, but the shock of a depth bomb explosion had put the electric-lighting system out of commission, and the crew, unnerved by the explosion and terrified by the darkness, had overpowered their officers and brought the boat to the surface.

EYES IN THE SEA

There were other craft that _Herr Kommandant_ had to look out for. His were not the only submarines in the sea. His foes also were possessed of submarines. They could not see under water any better than he could, but they could fight on the surface as well as he, and they could creep up on him even as he crept up on his prey. As a French submarine commander puts it: "The U-boats used to enjoy the advantage of remaining themselves invisible while all the surface and aërial craft which were sent in pursuit of them were boldly outlined against the sky and visible to them. This is one of the reasons we used submarines to ambush U-boats." Submarines were also used to accompany the convoys, so that the U-boat commander had to watch not only for the eyes of the ship's lookouts and the eyes in the kite balloons, but also for the periscope eyes that swam in the sea.

TRAILING U-BOATS BY SOUND

The troubles of the submarine-commander were multiplying. All over the world inventors were plotting his destruction. As long as we depended upon our eyes to ferret him out, the sea was a safe refuge, provided he dived deep enough, but when we began to use our ears as well, he found himself in a very serious predicament. Although light is badly broken up in its passage through water, sound-waves will travel through water much better than in air. The first listening-devices used were crude affairs and did not amount to much, particularly when the U-boats muffled their motors and engines so that they were virtually noiseless. But the French invented a very sensitive sound-detector. It consisted of a lot of tiny diaphragms set in a big hemisphere. There were two of these hemispheres, one at each side of the boat. When sound-waves struck these hemispheres, the diaphragms would respond. At the focus of each hemisphere there was a megaphone receiver; one of these carried the sound to the operator's right ear and the other to his left. He would turn a megaphone around until he found the diaphragm that produced the loudest sound. This gave him the direction of the sound-wave. Then the boat would be steered in that direction. He knew that it was aimed properly when the sound coming to his right ear was just as loud as that which came into his left ear.

A still better hydrophone was developed by a group of American inventors. The details of this cannot yet be disclosed, but we know that it was adopted at once by our allies. A very sensitive receiver was used which could detect a U-boat miles away and determine its direction accurately. Under ideal conditions the range of the device was from fifteen to twenty-five miles, but the average was from three to eight miles. If two or more boats fitted with sound-detectors were used, they could determine the position of the U-boat perfectly. One drawback was that the vessel would have to stop so that the noise of its own engines would not disturb the listener, but this was largely overcome by trailing the detector a hundred feet or more from the stem of the ship. The sounds were then brought in by an electric cable to the listener in the ship.

These sound-detectors were placed on Allied submarines as well as surface vessels and they were actually tried out on balloons and dirigibles, so that they could follow a U-boat after it had submerged too deeply to be followed by sight.

Many U-boats were chased to their doom by the aid of the American hydrophone. Fig. 21 illustrates a very dramatic chase. The full line shows the course of the U-boat as plotted out by hydrophones and the broken line the course of the submarine-chasers. The dots represent patterns of depth bombs dropped upon the U-boat. Try as he would, the _Herr Kommandant_ could not shake off his pursuers. At one time, as the listeners stopped to take observations, they heard hammering in the U-boat as if repairs were being made. The motors of the submarine would start and stop, showing clearly that it was disabled. More depth bombs were dropped and then there was perfect silence, which was soon broken by twenty-five revolver-shots. Evidently the crew, unable to come to the surface, had given up in despair and committed suicide.

The Adriatic Sea was an ideal place for the use of the hydrophone. The water there is so deep that submarines dared not rest on the bottom, but had to keep moving, and so they could easily be followed. Across the sea, at the heel of the boot of Italy, a barrage of boats was established. U-boats would come down to this barrage at night and, when within two or three miles of the boats, dive and pass under them. But when hydrophones were used that game proved very hazardous. Our listeners would hear them coming when they were miles away. Then they would hear them shift from oil-to electric-drive and plunge under the surface. Darkness was no protection to the U-boats. The sound-detector worked just as well at night as in the daytime and a group of three boats would drop a pattern of bombs that would send the U-boat to the bottom.

On one occasion after an attack it was evident that the submarine had been seriously injured. Its motors were operating, but something must have gone wrong with its steering-gear, or its ballast-chambers may have been flooded, because it kept going down and soon the listeners heard a crunching noise as it was crushed by the tremendous pressure of the water.

And so U-boat warfare grew more and more terrible for _Herr Kommandant_. The depths of the sea were growing even more dangerous than the surface. On every hand he was losing out. He had tried to master the sea without mastering the surface of the sea. But he can never really master who dares not fight out in the open. For a time, the German did prevail, but his adversaries were quick to see his deficiencies and, by playing upon these, to rob the terror of the sea of his powers. And as _Herr Kommandant_ looks back at the time when he stepped into the lime-light as the most brutal destroyer the world has ever seen, he cannot take much satisfaction in reflecting that the sum total of his efforts was to spread hatred of Germany throughout the world, to summon into the conflict a great nation whose armies turned the tide of victory against his soldiers, and finally to subject his navy, second only to that of Great Britain, to the most humiliating surrender the world has ever seen.