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.
In modern warfare a duel between fixed forts and floating forts is almost certain to end in a draw. Because the former are fixed they make good targets, while the war-ship, being able to move about, can dodge the shell that are fired against it. On the other hand, a fort on land can stand a great deal of pounding and each of its guns must be put out of action individually, before it is subdued, while the fort that is afloat runs the risk of being sunk with a few well-directed shots.
But fortifications alone will not protect a harbor from a determined enemy. They cannot prevent hostile ships from creeping by them under cover of darkness or a heavy fog. To prevent this, the harbor must be mined, and this must be done in such a way that friendly shipping can be piloted through the mine-field, while hostile craft will be sure to strike the mines and be destroyed.
The mines may be arranged to be fired by electricity from shore stations, in which case they are anchored at such a depth that ships can sail over them without touching them. If a hostile vessel tried to dash into the harbor, the touch of a button on shore would sink it when it passed over one of the mines. But the success of electrically fired mines would depend upon the "seeing." In a heavy fog they would prove no protection.
Another way of using electric mines is to have telltale devices which a ship would strike and which would indicate to the operator on shore that a vessel was riding over the mines and would also let him know over which particular mines it was at the moment passing. No friendly vessel would undertake to enter the harbor in a fog or after dark and the operator would not hesitate to blow up the invader even if he could not see him.
However, the ordinary method of mining a harbor is to lay fields of anchored mines across the channels and entrances to the harbor—sensitive mines that will blow up at the slightest touch of a ship's hull—and leave tortuous passages through the fields for friendly shipping. Of course pilots have to guide the ships through the passages and lest enemy spies learn just where the openings are the mine-fields must be shifted now and then.
The mines are, therefore, made so that they can be taken up by friendly mine-sweepers who know just how to handle them, and planted elsewhere. These are defensive mines, but there are other mines that are not intended to be moved. They are planted in front of enemy harbors to block enemy shipping and they are made so sensitive or of such design that they will surely explode if tampered with.
A favorite type of mine used during the war was one which automatically adjusted itself to sink to the desired depth. Submerged mines are more dangerous to the enemy because they cannot be seen and avoided. They should float far enough under the surface to remain hidden and yet not so deep that a shallow-draft ship can pass over them without hitting them. As the sea bottom may be very irregular, it is impossible to tell how long the anchor cable should be without sounding the depth of the water at every point at which a mine is planted. But the automatic anchor takes care of this. Very ingeniously it does its own sounding and holds the mine down to the depth for which it is set. The mine cable is wound up on a reel in the anchor and the mine is held fast to the anchor by a latch. The anchor is of box-shape or cylindrical form, with perforations in it. At first it sinks comparatively slowly, but as it fills with water it goes down faster. Attached to the anchor is a plummet or weight, connected by a cord to the latch. The length of this cord determines the depth at which the mine will float.
The operation of the mine is shown in Fig. 22. When it is thrown overboard (1) it immediately turns over so that the buoyant mine A floats on the surface (2). While the anchor is slowly filling and sinking, the plummet B runs out (3). If the mines are to float at a depth of, say, ten feet, this cord must be ten feet long. As soon as it runs out to its full length (4) it springs a latch, C, releasing the mine A. Then the mine cable D pays out, as the anchor E sinks, until the plummet B strikes bottom (5). As soon as the plummet cord slackens a spring-pressed pawl is released and locks the mine-cable reel, so that as the anchor continues to sink it draws the mine down with it, until it touches bottom (6), and as the anchor was ten feet from the bottom when the plummet touched bottom and locked the reel, the mine must necessarily be dragged down to a depth of ten feet below the surface.
The mine itself, or the "devil's egg" as it is called, is usually a big buoyant sphere of metal filled with TNT or some other powerful explosive; and projecting from it are a number of very fragile prongs which if broken or even cracked will set off the mine. There is a safety-lever or pin that makes the mine harmless when it is being handled, and this must be withdrawn just before the mine is to be launched. In some mines the prongs are little plungers that are withdrawn into the mine-shell and held by a cement which softens after the mine is submerged and lets the plungers spring out. When the plungers are broken, water enters and, coming in contact with certain chemicals, produces enough heat to set off a cartridge which fires the mine.
The enemy mine-fields were often located by seaplanes and then mine-sweepers had to undertake the extremely hazardous task of raising the mines or destroying them. If they were of the offensive type, it was much better to destroy them. But occasionally, when conditions permitted, mine-sweepers undertook to raise the mines and reclaim them for future use against the enemy. The work of seizing a mine and making it fast to the hoisting-cable of the mine-sweeper was usually done from a small rowboat. Raising the first mine was always the most perilous undertaking, because no one knew just what type of mine it was and how to handle it with safety, or whether there was any way in which it could be made harmless. There were some mines, for instance, that contained within them a small vial partly filled with sulphuric acid. The mine carried no prongs, but if it were tilted more than twenty degrees the acid would spill out and blow up the mine. Such a mine would be exceedingly difficult if not impossible to handle from a boat that was rocked about by the waves.
After the first mine of the field was raised and its safety-mechanism studied, the task of raising the rest was not so dangerous. A water telescope was used to locate the mine and to aid in hooking the hoisting-cable into the shackle on the mine. The hook was screwed to the end of a pole and after the mine was hooked, the pole was unscrewed and the cable hauled in, bringing up the "devil's egg" bristling with death. Care had to be taken to keep the bobbing boat from touching the delicate prongs until the safety-device could be set.
However, this painstaking and careful method of raising mines was not often employed. Shallow-draft mine-sweepers would run over the mine-field, dragging a cable between them. The cable would be kept down by means of hydrovanes or "water kites" deep enough to foul the anchor cables of the mines. The "water kites" were V-shaped structures that were connected to the cable in such a way that they would nose down as they were dragged through the water and carry the cable under. The action is just the reverse of a kite, which is set to nose up into the wind and carry the kite up when it is dragged through the air. By means of the cable the anchor chain of the mine was caught and then the mine with its anchor was dragged up. If the mine broke loose from its anchor it could be exploded with a rifle-shot if it did not automatically explode on fouling the cable.
When England entered the war she mined her harbors because, although she had the mastery of the sea, she had to guard against raids of enemy ships carried out in foggy and dark weather. But the mines were no protection against submarines. They would creep along the bottom under the mines. Then cable nets were stretched across the harbor channels to bar the submarines, but the U-boats were fitted with cutters which would tear through the nets, and it became necessary to use mines set at lower depths so that the submarines could not pass under them; and nets were furnished with bombs which would explode when fouled by submarines. In fact, mines were set adrift with nets stretched between them, to trap submarines. Floating mines were also used by the Germans for the destruction of surface vessels and these were usually set adrift in pairs, with a long cable connecting them, so that if a vessel ran into the cable the mines would be dragged in against its hull and blow it up.
The laws of war require that floating mines be of such a design that they will become inoperative in a few hours; otherwise they might drift about for weeks or months or years and be a constant menace to shipping. Sometimes anchored mines break away from their moorings and are carried around by ocean currents or are blown about by the winds. A year after the Russo-Japanese War a ship was blown up by striking a mine that had been torn from its anchorage and had drifted far from the field in which it was planted. No doubt there are hundreds of mines afloat in the Atlantic Ocean which for many years to come will hold out the threat of sudden destruction to ocean vessels; for the Germans knew no laws of war and had no scruples against setting adrift mines that would remain alive until they were eaten up with rust.
The chart on the next page shows the course of ocean currents in the North Atlantic as plotted out by the Prince of Monaco, from which it may be seen that German mines will probably make a complete circuit of the North Atlantic, drifting down the western coast of Europe, across the Atlantic, around the Azores, and into the Gulf Stream, which will carry them back to the North Sea, only to start all over. (See Fig. 23.) Some of them will run up into the Arctic Ocean, where they will be blown up by striking icebergs and many will be trapped in the mass of floating seaweed in the Sargasso Sea. But many years will pass before all danger of mines will be removed. In the meantime, the war has left a tremendous amount of work to be done in raising anchored mines and destroying them.
Early in the war the British were astonished to find enemy mine-fields in their own waters, far from any German ports. They could not have been planted by surface mine-layers, unless these had managed to creep up disguised as peaceful trawlers. This seemed hardly likely, because these fields appeared in places that were well guarded. Then it was discovered that German U-boats were doing this work. Special mine-laying U-boats had been built and one of them was captured with its cargo of "devil's eggs."
A sectional view of the mine-laying U-boat is shown opposite page 272. In the after part of the boat were mine-chutes in each of which three mines were stored. A mine-laying submarine would carry about a score of mines. These could be released one at a time. The mine with its anchor would drop to the bottom. As soon as it struck, anchor-arms would be tripped and spread out to catch in the sand or mud, while the mine cable would be released and the mine would rise as far as the cable would allow it. The U-boat commander would have to know the depth of water in which the mines were to be laid and adjust the cables to this depth in advance. This could not be done while the U-boat was submerged. With the mines all set for the depth at a certain spot, the U-boat commander had to find that very spot to lay his "eggs," otherwise they would either lie too deep to do any harm to shipping, or else they would reach up to the surface, where they might be discovered by the Allied patrols. As he had to do his navigating blindly, by dead-reckoning, it was very difficult for him to locate his mine-fields properly.
But the Germans did not have a monopoly on submarine mine-laying. The British also laid mines by submarine within German harbors and channels, right under the guns of Heligoland, and many a U-boat was destroyed by such mines within its home waters.
On the other hand, the Allies had a way of sailing right through fields of enemy mines with little danger. Our ships were equipped with "paravanes" which are something like the "water kites" used by mine-sweepers, and they are still used in the waters of the war zone. Paravanes are steel floats with torpedo-shaped bodies and a horizontal plane near the forward end. At the tail of the paravane, there are horizontal and vertical rudders which can be set to make the device run out from the side of the vessel that is towing it, and at the desired depth below the surface. Two paravanes are used, one at each side of the ship, and the towing-cables lead from the bow of the vessel. Thus there are two taut cables that run out from the ship in the form of a V and at such a depth that they will foul the mooring-cable of any mine that might be encountered. The mine cable slides along the paravane cable and in this way is carried clear of the ship's hull. When it reaches the paravane it is caught in a sharp-toothed jaw which cuts the mine cable and lets the mine bob up to the surface. The mine is then exploded by rifle or machine-gun fire.
In some forms of paravane there is a hinged jaw which is operated from the ship to shear the cable. The jaw is repeatedly opened and closed by a line that runs to a winch on the ship. This winch winds up the line until it is taut and then the line is permitted to slip, letting the jaw open, only to close again as the winch keeps on turning and winding up the line.
Guarded by steel sharks on each side, their jaws constantly working, a ship can plow right through a field of anchored mines with little danger. To be sure, the bow might chance to hit a mine, when, of course, there would be an explosion; but the ship could stand damage here better than anywhere else and unless the bow actually hit the mine, one or other of the paravanes would take care of it and keep it from being dragged in against the hull of the vessel.
According to German testimony, mines were responsible for the failure of the U-boat. However, it was not merely the scattered mine-fields sown in German waters that brought the U-boat to terms, but an enormous mine-field stretching across the North Sea from the Orkney Islands to the coast of Norway. Early in the war, U-boats had been prevented from entering the English Channel by nets and mines stretched across the Straits of Dover. As the submarine menace grew, it was urged that a similar net be stretched across the North Sea to pen the U-boats in. But it seemed like a stupendous task. The distance across at the narrowest point is nearly two hundred and fifty miles. It would not have been necessary to have the net come to the surface. It could just as well have been anchored so that its upper edge would be covered with thirty feet of water. Surface vessels could then have sailed over it without trouble and submarines could not have passed over it without showing themselves to patrolling destroyers. It would not have been necessary to carry the net to the bottom of the sea. A belt of netting a hundred and fifty feet wide would have made an effective bar to the passage of U-boats. As U-boats might cut their way through the net, it was proposed to mount bombs or mines on them which would explode on contact and destroy any submarine that tried to pass. However, laying a net two hundred feet long even when it is laid in sections, is no small job, but when the net is loaded with contact mines, the difficulty of the work may be well imagined.
And yet had it been thought that the net would be a success it would have been laid anyhow, but it was argued that seaweed would clog the meshes of the net and ocean currents would tear gaps in it. Even if it had not been torn away, the tidal currents would have swept it down and borne it under so far that U-boats could have passed over it in safety without coming to the surface.
When America entered the war, we were very insistent that something must be done to block the North Sea, and we proposed that a barrage of anchored mines be stretched across the sea and that these mines be set at different levels so as to make a "wall" that submarines could not dive under. This would do away with all the drawbacks of a net. Ocean currents and masses of seaweed could not affect individual mines as they would a net. Furthermore, an American inventor had devised a new type of mine which was peculiarly adapted to the proposed mine barrage. It had a firing-mechanism that was very sensitive and the mine had twice the reach of any other.
At length the British mine-laying forces were prevailed upon to join with us in laying this enormous mine. It was one of the biggest and most successful undertakings of the war. It was to be two hundred and thirty miles long and twelve miles wide on the average, reaching from the rocky shores of the Orkney Islands to Norway. There was plenty of deep water close to the coast of Norway and it was against international law to lay mines within three miles of the shores of a neutral nation, so that the U-boats might have had a clear passage around the end of the barrage. But as it was also against the law for the U-boats to sail through neutral waters, Norway laid a mine-field off its coast to enforce neutrality, and this was to join with that which the British and we were to lay. Most of the mine-laying was to be done by the United States and we were to furnish the mines.
The order to proceed with the work was given in October, 1917, and it was a big order. A hundred thousand mines were to be made and to preserve secrecy, as well as to hurry the work as much as possible, it was divided among five hundred contractors and subcontractors. The parts were put together in one plant and then sent to another, where each mine was filled with three hundred pounds of molten TNT. To carry them across the ocean small steamers were used, so that if one should be blown up by a submarine the loss of mines would not be very great. There were twenty-four of these steamers, each carrying from twelve hundred to eighteen hundred mines and only one of them was destroyed by a submarine. The steamers delivered their loads on the west coast of Scotland and the mines were taken across to the east coast by rail and motor canal-boats. Here the mines were finally assembled, ready for planting. Seventy thousand mines were planted, four fifths of them by American mine-layers and the rest by the British.
To handle the mines the ships were specially fitted with miniature railroads for transporting the mines to the launching-point, so that they could be dropped at regular intervals without interruption. Each anchor mine was provided with flanged wheels that ran on rails. The mines were carried on three decks and each deck was covered with a network of rails, switches, and turn-tables, while elevators were provided to carry the mines from one deck to another. The mines, like miniature railroad cars, were coupled up in trains of thirty or forty and as each mine weighed fourteen hundred pounds, steam winches had to be used to haul them. At the launching-point the tracks ran out over the stern of the boat and here a trap was provided which would hold only one mine at a time. By the pulling of a lever the jaws of the trap would open and the mine would slide off the rails and plunge into the sea.
The mines were dropped every three hundred feet in lines five hundred feet apart, as it was unsafe for the mine-layers to steam any closer to one another than that. The mines were of the type shown in Fig. 22 and automatically adjusted themselves to various depths. The depth of the water ran down to twelve hundred feet near the Norwegian coast. Never before had mines been planted at anywhere near that depth.
It was dangerous work, because the enemy knew where the mines were being planted, as neutral shipping had to be warned months in advance. The mine-layers were in constant danger of submarine attack, although they were convoyed by destroyers to take care of the U-boats. There was even danger of a surface attack and so battle-cruisers were assigned the job of guarding the mine-layers. The mine-layers steamed in line abreast, and had one of them been blown up, the shock would probably have been enough to blow up the others as well. Enemy mines were sown in the path of the mine-layers, so the latter had to be preceded by mine-sweepers. Navigation buoys had to be planted at the ends of the lines of mines and the enemy had a habit of planting mines near the buoys or of moving the buoys whenever he had a chance. But despite all risks the work was carried through.
The barrier was not an impassable one. With the mines three hundred feet apart, a submarine might get through, even though the field was twenty-five miles broad, but the hazards were serious. Before the first lines of mines had been extended half-way across, its value was demonstrated by the destruction of several U-boats, and as the safety-lane was narrowed down the losses increased. It is said that altogether twenty-three German submarines met their doom in the great mine barrage. U-boat commanders balked at running through it, and U-boat warfare virtually came to a standstill. According to Captain Bartenbach, commander of submarine bases in Flanders, three U-boats were sunk by anchored mines for every one that was destroyed by a depth bomb.
The war on the submarine was fought mainly from the surface of the sea and from the air above the sea, and naturally it resulted in many interesting naval developments.
As described in Chapter XIII, the first offensive measure against the U-boat was the building of swarms of speedy motor-boats which drove the invaders away from harbors and into the open sea. To follow the U-boats out into rough water larger submarine-chasers were built, but even they could not cope with the enemy far from the harbors.
The Italians made excellent use of speedy motor-boats in the protected waters of the Adriatic Sea. One type of motor-boat was equipped with two torpedo-tubes in the bow. Small 14-inch torpedoes were used, but as each torpedo carried two hundred pounds of high explosive, the motor-boat was a formidable vessel if it crept in close enough to discharge one of these missiles at its foe.
On one occasion, a patrol of these little boats sighted a couple of Austrian dreadnoughts headed down the coast, surrounded by a screen of ten destroyers. Favored by the mist, two of the motor-boats crept through the screen of destroyers, and torpedoed the battle-ships. Then they made good their escape. A destroyer that pursued one of the boats decided that the game was not worth while when it was suddenly shaken up by the explosion of a depth bomb dropped from the motor-boat.
The Italians showed a great deal of naval initiative. They were forever trying to trap the Austrian fleet or to invade its harbors. Like all other naval powers, the Austrians protected their harbors with nets and mines. It was impossible for submarines to make an entrance and the ports were too well fortified to permit an open attack on the surface. Nevertheless, the Italians did break through the harbor defenses on one or two occasions and sank Austrian war-vessels. Again it was with a small boat that they did the trick.
The nets which the Austrians stretched across their harbor entrance were supported on wooden booms or logs which served as floats. These booms offered an effective bar to small boats which might attempt to enter the harbor under cover of darkness. But the Italians found a way to overcome this obstruction. They built a flat-bottomed motor-boat which drew very little water. Running under the boat were two endless chains, like the treads of a tank. In fact, the boat came to be known as a "sea tank." The chains were motor-driven and had spiked sprockets, so that when a boom was encountered they would bite into the wood and pull the boat up over the log, or maybe they would drag the log down under the boat. At any rate, with this arrangement it was not very difficult to pass the boom and enter the harbor. At the rear the chains were carried back far enough to prevent the propeller from striking when the boat had passed over the log.
A curious boat that we undertook to furnish during the war was a cross between a destroyer and a submarine-chaser. After the submarine had been driven out to sea its greatest foe was undoubtedly the destroyer, and frantic efforts were made to turn out as many destroyers as possible. But it takes time to build destroyers and so a new type of boat was designed, to be turned out quickly in large numbers. A hundred and ten "Eagles" (as these boats are called) were ordered, but the armistice was signed before any of them were put into service; and it is just as well that such was the case, for in their construction everything was sacrificed to speed of production. As a consequence they are very ugly boats, with none of the fine lines of a destroyer, and they roll badly, even when the sea is comparatively peaceful. They are five-hundred-ton boats designed to make eighteen knots, which would not have been fast enough to cope with U-boats, because the latter could make as high a speed as that themselves, when traveling on the surface, and the two 4-inch guns of the Eagles would have been far outranged by the 5.9-inch guns of the larger U-boats.
When the war on the U-boat was carried up into the sky, many new naval problems cropped up, particularly when German submarines chose to work far out at sea. Big seaplanes were used, but they consumed a great deal of fuel in flying out and back, cutting down by just so much their flying-radius at the scene of activities. A special towing-barge was used. These barges had trimming-tanks aft, which could be flooded so that the stern of the barge would submerge. A cradle was mounted to run on a pair of rails on the barge. The body of the seaplane was lashed to this cradle and then drawn up on the barge by means of a windlass. This done, the water was blown out of the trimming-tanks by means of compressed air and the barge was brought up to an even keel. The barge with its load was now ready to be towed by a destroyer or other fast boat to the scene of operations. There water was again let into the trimming-tanks and the seaplane was let back into the water. From the water the seaplane arose into the air in the usual way.
Unfortunately, when the sea is at all rough it is exceedingly difficult for a seaplane to take wing, particularly a large seaplane. A better starting-platform than the sea had to be furnished. At first some seaplanes were furnished with wheels, so that they could be launched from platforms on large ships; and then, to increase the flying-radius, seaplanes were discarded in favor of airplanes. Once these machines were launched, there was no way for them to get back to the ship. They had to get back to land before their fuel was exhausted.
On the large war-vessels a starting-platform was built on a pair of long guns. Then the war-ship would head into the wind and the combined travel of the ship and of the airplane along the platform gave speed enough to raise the plane off the platform before it had run the full length of the guns. But as long as aviators had no haven until they got back to land, there were many casualties. Eager to continue their patrol as long as possible, they would sometimes linger too long before heading for home and then they would not have enough fuel left to reach land. Many an aviator was lost in this way, and finally mother-ships for airplanes had to be built.
The British Navy had constructed a number of very fast cruisers to deal with any raiders the Germans might send out. These cruisers were light vessels capable of such high speeds that they could even overtake a destroyer. They were 840 feet long and their turbines developed 90,000 horse-power. The construction of these vessels was for a long time kept a profound secret and it was not until the German fleet surrendered that photographs of them were allowed to be published. Because of this secrecy the boats were popularly known as "hush ships." They were not armored; it was not necessary to load them down with armor plate, because their protection lay in speed and they were designed to fight at very long range. In fact, they were to carry guns that would outrange those of the most powerful dreadnoughts. Our largest naval guns are of 16-inch caliber, but the "hush ships" were each to carry two 18-inch guns. The guns were monsters weighing 150 tons each and they fired a shell 18 inches in diameter and 7 feet long to a distance of 30 miles when elevated to an angle of 45 degrees. The weight of the shell was 3600 pounds and it carried 500 pounds of high explosive or more than is carried in the largest torpedoes.
At the 32-mile range the shell would pass through 12 inches of face-hardened armor and at half that range it would pass through armor 18 inches thick, and there is no armor afloat any heavier than this.
Armed with such powerful guns as these, the "hush ships" would have been very formidable indeed; but when the guns were mounted on one of the cruisers, the Furious, they were found too powerful for the vessel. It was evident that the monsters would very seriously rack their own ship. So the guns were taken off the cruiser and it was turned into a mother-ship for airplanes. A broad, unobstructed deck was built on the ship which provided a runway from which airplanes could be launched, and this runway was actually broad enough to permit airplanes to land upon it. Under the runway were the hangars in which the airplanes were housed. Other "hush ships" were also converted into airplane mother-boats and there were special boats built for this very purpose, although they were not able to make the speed of the "hush ships." One of these special boats had funnels that turned horizontally to carry off the furnace smoke over the stern and leave a perfectly clear flying-deck, 330 feet long.
As for the 18-inch guns, they were put to another use. Early in the war the British had need for powerful shallow-draft vessels which could operate off the Flanders coast and attack the coast fortifications that were being built by the Germans. The ships that were built to meet this demand were known as monitors, because like the famous "monitor" of our Civil War they carried a single turret. These monitors were very broad for their length and were very slow. At best they could make only seven knots and in heavy weather they could not make more than two or three knots.
To be made proof against torpedoes these boats were formed with "blisters" or hollow rounded swells in the hull at each side which extended out to a distance of twelve to fifteen feet. The blisters were subdivided into compartments, so that if a torpedo struck the ship it would explode against a blister at a considerable distance from the real hull of the ship and the force of the explosion would be expended in the compartments. The blisters were the salvation of the monitors. Often were the boats struck by torpedoes without being sunk.
Unfortunately, this form of protection could not be applied to ordinary vessels, because it would have interfered seriously with navigation. The blisters made the monitors very difficult to steer and hampered the progress of a ship, particularly in a seaway.
With ships such as these the British bombarded Zeebrugge from a distance of twenty to twenty-five miles. Of course, the range had to be plotted out mathematically, as the target was far beyond the horizon of the ship, and the firing had to be directed by spotters in airplanes.
At first guns from antiquated battle-ships were used in the monitors; then larger guns were used, until finally two of the monitors inherited the 18-inch guns of the Furious. A single gun was mounted on the after deck of each vessel and the gun was arranged to fire only on the starboard side. No heavily armored turret was provided, but merely a light housing to shelter the gun.
The British war-vessels that operated in the shallow waters off the coast of Flanders were a constant source of annoyance to the Germans. Because of the shallow water it was seldom possible for a submarine to creep up on them. A U-boat required at least thirty-five feet of water for complete submergence and it did not dare to attack in the open. This led the Germans to launch a motor-boat loaded with high explosive, which was steered from shore. The motor-boat carried a reel of wire which connected it with an operator on shore. There was no pilot in the boat, but the helm was controlled electrically by the man at the shore station. As it was difficult for the helmsman to see just what his boat was doing, or just how to steer it when it was several miles off, an airplane flew high above it and directed the helmsman, by radiotelegraphy, how to steer his boat. Of course, radiotelegraphy might have been used to operate the steering-mechanism of the boat, but there was the danger that the radio operators of the British might send out disturbing waves that would upset the control of the motor-boat, and so direct wire transmission was used instead. Fortunately, when the Germans tried this form of attack, an alert British lookout discovered the tiny motor-boat. The alarm was given and a lucky shot blew up the boat with its charge before it came near the British vessel.
Nearly fifteen million tons of shipping lie at the bottom of the sea, sunk by German U-boats, and the value of these ships with their cargo is estimated at over seven billion dollars. In one year, 1917, the loss was nearly a million dollars a day.
Of course these wrecks would not be worth anything like that now, if they were raised and floated. Much of the cargo would be so damaged by its long immersion in salt water that it would be absolutely valueless, but there are many kinds of merchandise that are not injured in the least by water. Every ship carries a certain amount of gold and silver; and then the ship's hull itself is well worth salving, provided it was not too badly damaged by the torpedo that sank it. Altogether, there is plenty of rich treasure in the sea awaiting the salvor who is bold enough to go after it.
To be sure, not all of the U-boat's victims were sunk in deep water. Many torpedoed vessels were beached or succeeded in reaching shallow water before they foundered. Some were sunk in harbors while they lay at anchor, before the precaution was taken of protecting the harbors with nets. The Allies did not wait for the war to end before trying to refloat these vessels. In fact, during the war several hundred ships were raised and put back into service. A special form of patch was invented to close holes torn by torpedoes. Electric pumps were built which would work under water and these were lowered into the holds of ships to pump them out. The salvors were provided with special gas-masks to protect them from poisonous fumes of decayed matter in the wrecks.
Our own navy has played an important part in salvage. Shortly after we entered the war, all the wrecking-equipment in this country was commandeered by the government and we sent over to the other side experienced American salvors, provided with complete equipment of apparatus and machinery.
The majority of wrecks, however, are found in the open sea, where it would have been foolish to attempt any salvage-operations because of the menace of submarine attack. On at least one occasion a salvage vessel, while attempting to raise the victims of a submarine, fell, itself, a prey to a Hun torpedo. Now that this menace has been removed, such vessels as lie in comparatively shallow water, and in positions not subject to sudden tempests, can be raised by the ordinary methods; or if it is impracticable to raise them, much of their cargo can be reclaimed. However, most of the torpedoed ships lie at such depths that their salvage would ordinarily be despaired of.
It will be interesting to look into conditions that exist in deep water. Somehow the notion has gone forth that a ship will not surely sink to the very bottom of the deep sea, but on reaching a certain level will find the water so dense that even solid iron will float, as if in a sea of mercury, and that here the ship will be maintained in suspension, to be carried hither and yon by every chance current. Indeed, it makes a rather fantastic picture to think of these lost ships drifting in endless procession, far down beneath the cold green waves, and destined to roam forever like doomed spirits in a circle of Dante's Inferno.
But the laws of physics shatter any such illusion and bid us paint a very different picture. Liquids are almost incompressible. The difference in density between the water at the surface of the sea and that at a depth of a mile is almost insignificant. As a matter of fact, at that depth the water would support only about half a pound more per cubic foot than at the surface. The pressure, however, would be enormous. Take the Titanic, for instance, which lies on the bed of the ocean in water two miles deep. It must endure a pressure of about two long tons on every square inch of its surface. Long before the vessel reached the bottom her hull must have been crushed in. Every stick of wood, every compressible part of her structure and of her cargo, must have been staved in or flattened. As a ship sinks it is not the water but the ship that grows progressively denser. The Titanic must have actually gained in weight as she went down, and so she must have gathered speed as she sank.
We may be certain, therefore, that every victim of Germany's ruthless U-boats that sank in deep water lies prone upon the floor of the sea. It matters not how or where it was sunk, whether it was staggered by the unexpected blow of the torpedo and then plunged headlong into the depths of the sea, or whether it lingered, mortally wounded, on the surface, quietly settling down until the waves closed over it. Theoretically, of course, a perfect balance might be reached which would keep a submerged vessel in suspension, but practically such a condition is next to impossible. Once a ship has started down, she will keep on until she reaches the very bottom, whether it be ten fathoms or ten hundred.
Instead of the line of wandering specters, then, we must conjure up a different picture, equally weird—an under-world shrouded in darkness; for little light penetrates the deep sea. Here in the cold blackness, on the bed of the ocean, the wrecks of vessels that once sailed proudly overhead lie still and deathly silent—some keeled over on their sides, some turned turtle, and most of them probably on even keel. Here and there may be one with its nose buried deep in the mud; and in the shallower waters we may come across one pinned down by the stern, but with its head buoyed by a pocket of air, straining upward and swaying slightly with every gentle movement of the sea, as if still alive.
This submarine graveyard offers wonderful opportunities for the engineer, because the raising of wrecked vessels is really a branch of engineering. It is a very special branch, to be sure, and one that has not begun to receive the highly concentrated study that have such other branches as tunneling, bridge-construction, etc. Nevertheless it is engineering, and it has been said of the engineer that his abilities are limited only by the funds at his disposal. Now he has a chance to show what he can do, for there are hundreds of vessels to be salved where before there was but one. The vast number of wrecks in deep water will make it pay to do the work on a larger and grander scale than has been possible heretofore. Special apparatus that could not be built economically for a single wreck may be constructed with profit if a number of vessels demanding similar treatment are to be salved.
The principal fields of German activities were the Mediterranean Sea and the waters surrounding the British Isles. Although the submarine zone covered some very deep water, where the sounding-lead runs down two miles without touching bottom, obviously more havoc could be wrought near ports where vessels were obliged to follow a prescribed course, and so most of the U-boat victims were stricken when almost in sight of land. In fact, as was pointed out in a previous chapter, it was not until efficient patrol measures made it uncomfortable for the submarines that they pushed out into the open ocean to pursue their nefarious work. The Lusitania went down only eight miles from Old Head of Kinsale, in fifty fathoms of water.
If we draw a line from Fastnet Rock to the Scilly Islands and from there to the westernmost extremity of France, we enclose an area in which the German submarines were particularly active. The soundings here run up to about sixty fathoms in some places, but the prevailing depth is less than fifty fathoms. In the North Sea, too, except for a comparatively narrow lane along the Norwegian coast—which, by the way, marked the safety lane of the German blockade zone—the chart shows fifty fathoms or under. If our salvors could reach down as far as that, most of the submarine victims could be reclaimed. But fifty fathoms means 300 feet, which is a formidable depth for salvage work. Only one vessel has ever been brought up from such a depth and that was a small craft, one of our submarines, the F-4, which sank off the coast of Hawaii four years ago.
There are four well-known methods of raising a vessel that is completely submerged. Of course, if the ship is not completely submerged, the holes in her hull may be patched up, and then when her hull is pumped out, the sea itself will raise the ship, unless it be deeply embedded in sand or mud. If the vessel is completely submerged, the same process may be resorted to, but first the sides of the hull must be extended to the surface to keep the water from flowing in as fast as it is pumped out. It is not usual to build up the entire length of the ship. If the deck is in good condition, it may suffice to construct coffer-dams or walls around several of the hatches. But building up the sides of a ship, or constructing coffer-dams on the ship's deck is a difficult task, at best, because it must be done under water by divers.
A record for this type of salvage work was established by the Japanese when they raised the battle-ship Mikasa that lay in some eighty feet of water. Her decks were submerged to a depth of forty feet. It is doubtful that this salvage work could be duplicated by any other people of the world. The wonderful patriotism and loyalty of the Japanese race were called forth. It is no small task to build a large coffer-dam strong enough to withstand the weight of forty feet of water, or a pressure of a ton and a quarter per square foot, even when the work is done on the surface. Perfect discipline and organized effort of the highest sort were required. Labor is cheap in Japan and there was no dearth of men for the work. Over one hundred divers were employed. In addition to the coffer-dam construction much repair work was necessary. Marvelous acts of devotion and heroism were performed. It is rumored that in some places it was necessary for divers to close themselves in, cut their air supply-pipes and seal themselves off from the slightest chance of escape; and that there were men who actually volunteered to sacrifice their lives in this way for their beloved country and its young navy. Where, indeed, outside of the Land of the Rising Sun could we find such patriotic devotion!
A second salvage method consists in building a coffer-dam not on the ship but around it, and then pumping this out so as to expose the ship as in a dry-dock. Such was the plan followed out in recovering the Maine. Obviously, it is a very expensive method and is used only in exceptional cases, such as this, in which it was necessary to make a post-mortem examination to determine what caused the destruction of the vessel. Neither of these methods of salvage will serve for raising a ship sunk in deep water.
A salvage system that has come into prominence within recent years consists in pumping air into the vessel to drive the water out, thus making the boat light enough to float. This scheme can be used only when the deck and bulkheads of the boat are strongly built and able to stand the strain of lifting the wreck, and when the hole that sank the vessel is in or near the bottom, so as to allow enough airspace above it to lift the boat. The work of the diver in this case consists of closing hatches and bulkhead doors, repairing holes in the upper part of the hull, and generally strengthening the deck. It must be remembered that a deck is built to take the strain of heavy weights bearing down upon it. It is not built to be pushed up from beneath, so that frequently this method of salving is rendered impracticable because the deck itself cannot stand the strain.