CHAPTER XVI

RECLAIMING THE VICTIMS OF THE SUBMARINE

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.

IN THE DEPTHS OF THE SEA

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.

A SUBMARINE GRAVEYARD

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.

DIFFERENT WAYS OF SALVING A WRECK

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.

RAISING A SHIP ON AIR

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.

A more common salvage method consists in passing cables or chains under the wreck and attaching them to large floats or pontoons. The slack in the chains is taken up when the tide is low, so that on the turn of the tide the wreck will be lifted off the bottom. The partially raised wreck is then towed into shallower water, until it grounds. At the next low tide, the slack of the chains is again taken in, and at flood-tide the wreck is towed nearer land. The work proceeds step by step, until the vessel is moved inshore far enough to bring its decks awash; when it may be patched up and pumped out. Where the rise of the tide is not sufficient to be of much assistance, hydraulic jacks or other lifting-apparatus are used.

SALVING THE U. S. SUBMARINE F-4

If the salvor could always be assured of clear weather, his troubles would be reduced a hundredfold, but at best it takes a long time to perform any work dependent upon divers, and the chances are very good when they are operating in an unsheltered spot, that a storm may come up at any time and undo the result of weeks and months of labor. This is what happened when the submarine _F-4_ was salved. After a month of trying effort the submarine was caught in slings hung from barges, lifted two hundred and twenty-five feet, and dragged within a short distance of the channel entrance of the harbor, where the water was but fifty feet deep. But just then a violent storm arose, which made the barges surge back and forth and plunge so violently that the forward sling cut into the plating of the submarine and crushed it. The wreck had to be lowered to the bottom and the barges cut free to save them from being smashed. At the next attempt to raise the _F-4_ pontoons were again used, but instead of being arranged to float on the surface, they were hauled down to the wreck and made fast directly to the hull of the submarine. Then when the water was forced out of the pontoons with compressed air, they came up to the surface, bringing the submarine with them. In this way all danger of damage due to sudden storms was avoided because water under the surface is not disturbed by storms overhead; and when the wreck was floated, the pontoons and submarine formed a compact unit.

While this method of salvage seems like a very logical one for work in the open sea, one is apt to forget how large the pontoons must be to lift a vessel of any appreciable size. Not only must they support their own dead weight, together with that of the sunken vessel, but some allowance must usually be made for dragging the wreck out of the clutches of a sandy or muddy bottom. Imagine the work of building pontoons large enough to raise the _Lusitania_. They would have to have a combined displacement greater than that of the vessel itself, and they would have to be so large that they would be very unwieldy things to handle in a seaway. It is for this reason that submarine pontoons are not often used to take the entire weight of the vessel. So far they have been employed mainly to salve small ships and then only to take a portion of the weight, the principal work being done by large wrecking-cranes. Instead of horizontal pontoons it has been suggested that vertical pontoons be employed, so as to provide a greater lifting-power without involving the use of enormous unwieldy units.

Ships are not built so that they can be picked up by the ends. Such treatment would be liable to break their backs in the middle. Were they built more like a bridge truss, the salvor's difficulties would be materially lessened. It would be a much simpler matter to raise a vessel with pontoons were it so constructed that the chains of the pontoon could be attached to each end of the hull. But because a ship is built to be supported by the water uniformly throughout its length, the salvor must use a large number of chains, properly spaced along the hull, so as to distribute the load uniformly and see that too much weight does not fall on this or that pontoon.

The main problem, however, is to get hold of the wreck and this requires the services of divers, so that if there were no other limiting factor, the depth to which a diver may penetrate and perform his duties sets the mark beyond which salvage as now conducted is impossible.

A common diver's suit does not protect the diver from hydraulic pressure. Only a flexible suit and a thin layer of air separates him from the surrounding water. This air must necessarily be of the same pressure as the surrounding water. The air that is pumped down to the diver not only serves to supply his lungs, but by entering his blood transmits its pressure to every part of his anatomy. As long as the external pressure is equalized by a corresponding pressure within him, the diver experiences no serious discomfort. In fact, when the pressure is not excessively high he finds it rather exhilarating to work under such conditions; for, with every breath, he takes in an abnormal amount of oxygen. When he returns to the surface he realizes that he has been working under forced draft. He is very much exhausted and he is very hungry. It takes a comparatively short time to build up the high internal pressure, which the diver must have in order to withstand the pressure of the water outside, but it is the decompression when he returns to the surface that is attended with great discomfort and positive danger. If the decompression is not properly effected, the diver will suffer agonies and even death from the so-called "Caisson Disease."

A HUMAN SODA-WATER BOTTLE

We know now a great deal more than we used to know about the effect of compressed air on the human system, and because of this knowledge divers have recently descended to depths undreamed of a few years ago. When a diver breathes compressed air, the oxygen is largely consumed and exhaled from the lungs in the form of carbon-dioxide, but much of the nitrogen is dissolved in the blood and does not escape. However, like a bottle of soda-water, the blood shows no sign of the presence of the gas as long as the pressure is maintained. But on a sudden removal of the pressure, the blood turns into a froth of nitrogen bubbles, just as the soda-water froths when the stopper of the bottle is removed. This froth interrupts the circulation. The release of pressure is felt first in the arteries and large veins. It takes some time to reach all the tiny veins, and serious differences of pressure are apt to occur that often result in the rupture of blood-vessels. The griping pains that accompany the "Caisson Disease" are excruciating. The only cure is to restore the blood to its original pressure by placing the patient in a hospital lock, or boiler-like affair, where compressed air may be admitted; and then to decompress the air very slowly.

It is possible to relieve the pressure in a bottle of soda-water so gradually that the gas will pass off without the formation of visible bubbles, and that is what is sought in decompressing a diver. After careful research it has been found that the pressure may be cut down very quickly to half or even less of the original amount, but then the diver must wait for the decompression to extend to the innermost recesses of his being and to all the tiny capillaries of his venous system.

In the salvage of the _F-4_ a diver went down 306 feet, and remained on the bottom half an hour. The pressure upon him was 135 pounds per square inch, or about 145 tons on the surface of his entire body. Some idea of what this means may be gained if we consider that the tallest office building in the world does not bear on its foundations with a greater weight than 215 pounds to the square inch or only about 50 per cent more than the crushing pressure this diver had to endure.

It took the diver a very short time to go down. On coming up he proceeded comparatively rapidly until he reached a depth of 100 feet. There he found the bottom rung of a rope ladder. On it he was obliged to rest for several minutes before proceeding to the next rung. The rungs of this ladder were 10 feet apart, and on each rung the diver had to rest a certain length of time, according to a schedule that had been carefully worked out. At the top rung, for instance, only 10 feet from the surface, he was obliged to wait forty minutes. In all, it took him an hour and forty-five minutes to come up to the surface. The decompression was complete and he suffered no symptoms of the "Caisson Disease." But he was so exhausted from his efforts that he was unfit for work for several days. Yet the operations that he performed at the depth of 300 feet would not have taken more than a few minutes on the surface.

A SUBMARINE REST-CHAMBER

The Germans have paid a great deal of attention to deep-diving operations, and no doubt while their U-boats were sinking merchant ships German salvors were anticipating rich harvests after hostilities ended. One scheme they developed was a submarine rest-chamber which could be permanently located on the bottom of the sea close to the point where the salvage operations were to take place. This chamber consists of a large steel box which is supplied with air from the surface and in which divers may make themselves comfortable when they need a rest after arduous work. Entrance to the chamber is effected through a door in the floor. The pressure of the air inside prevents the water from rising into the chamber and flooding it. From this submarine base the divers may go out to the wreck, either equipped with the ordinary air-tube helmets or with self-regenerating apparatus which makes them independent of an air-supply for a considerable period of time. When the diver has worked for an hour or two, or when he is tired, he may return to this chamber, remove his helmet, eat a hearty meal, take a nap if he needs it, and then return to the salvage work without going through the exhausting operation of decompressing.

CUTTING METAL UNDER WATER WITH A TORCH

The work of the diver usually consists of far more than merely passing lines under a sunken hull. It is constantly necessary for him to cut away obstructing parts. He must sometimes use blasting-power. Pneumatic cutting-tools frequently come into play, but the Germans have lately devised an oxy-hydrogen torch for underwater use, with which the diver can cut metal by burning through it. This is accomplished by using a cup-shaped nozzle through which a blast of air is projected under such pressure that it blows away the water over the part to be cut. The oxygen and hydrogen jets are then ignited electrically, and the work of cutting the metal proceeds in the hole in the water made by the air-blast. A similar submarine torch has recently been developed by an American salvage company. It was employed successfully in cutting drainage-holes in the bulkheads of the _St. Paul_, which was raised in New York Harbor in the summer of 1918.

EXPLORING THE SEA BOTTOM IN A DIVER'S SLED

The diver's sled is still another interesting German invention. It is a sled provided with vertical and horizontal rudders, which is towed by means of a motor-boat at the surface. The diver, seated on the sled, and provided with a self-contained diving-suit, can direct the motor-boat by telephone and steer his sled up and down and wherever he chooses. And so without any physical exertion, he can explore the bottom of the sea and hunt for wrecks.

ARMORED DIVING-SUITS

From time to time attempts have been made to construct a diver's suit that will not yield to the pressure of the sea, so that the diver will not be subjected to the weight of the water about him, but can breathe air at ordinary atmospheric pressure. Curious armor of steel has been devised, with articulated arms and legs, in which the diver is completely encased. With the ordinary rubber suit, the diver usually has his hands bare, because he is almost as dependent upon the sense of touch as a blind man. But where the pressure mounts up to such a high degree that a metal suit must be used, no part of the body may be exposed. If a bare hand were extended out of the protecting armor it would immediately be mashed into a pulp and forced back through the opening in the arms of the suit. The best that can be done, then, is to furnish the arms of the suit with hooks or tongs or other mechanical substitutes for hands which will enable the diver to make fast to the wreck or various parts of it.

But if a diver feels helpless in the bag of a suit now commonly worn, what would he do when encased in a steel boiler; for that is virtually what the armored suit is! A common mistake that inventors of armor units have made is to fail to consider the effects of the enormous hydraulic pressure on the joints of the suit. In order to make them perfectly tight, packings must be employed, and these are liable to be so jammed by the hydraulic pressure that it is well nigh impossible to articulate the limbs. Again, the construction of the suit should be such that when a limb is flexed it would not displace any more water than when in an extended position, and vice versa. A diver may find that he cannot bend his arm, because in doing so he would expand the cubical content of his armor by a few cubic inches, and to make room for this increment of volume it would be necessary for him to lift several hundred pounds of water. The hydraulic pressure will reduce the steel suit to its smallest possible dimensions, which may result either in doubling up the members or extending them rigidly.

But these difficulties are not insuperable. There is no reason why a steel manikin cannot be constructed with a man inside to direct its movements.

THE SALVOR'S SUBMARINE

Other schemes have been devised to relieve the diver of abnormally high air-pressure. One plan is to construct a large spherical working-chamber strong enough to withstand any hydraulic pressure that might be encountered. This working-chamber is equipped with heavy glass ports through which the workers can observe their surroundings in the light of an electric search-light controlled from within the chamber. The sphere is to be lowered to the wreck from a barge, with which it will be in telephonic communication and from which it will be supplied with electric current to operate various electrically driven mechanisms. By means of electromagnets this sphere may be made fast to the steel hull of the vessel and thereupon an electric drill is operated to bore a hole in the ship and insert the hook of a hoisting-chain. This done, the sphere would be moved to another position, as directed by telephone and another chain made fast. The hoisting-chains are secured to sunken pontoons and after enough of the chains have been attached to the wreck the pontoons are pumped out and the wreck is raised.

It is a pity that ship-builders have not had the forethought to provide substantial shackles at frequent intervals firmly secured to the framing. A sunken vessel is really a very difficult object to make fast to and the Patent Office has recorded many very fantastic schemes for getting hold of a ship's hull without the use of divers. One man proposes the use of a gigantic pair of ice-tongs; and there have been no end of suggestions that lifting-magnets be employed, but no one who has any idea of how large and how heavy such magnets must be would give these suggestions any serious consideration.

But, after all, the chief obstacle to salvage in the open sea is the danger of storms; months of preparation and thousands of dollars' worth of equipment may be wiped out in a moment.

FIGHTING THE WAVES WITH AIR

However, there has been another recent development which may have a very important bearing on this problem of deep-sea salvage work. It has often been observed that a submerged reef, twenty or thirty feet below the surface, may act as a breakwater to stop the storming waves. An inventor who studied this phenomenon arrived at the theory that the reefs set up eddies in the water which break up the rhythm of the waves and convert them into a smother of foam just above the reef. Thereupon he conceived the idea of performing the same work by means of compressed air. He laid a pipe on the sea bottom, forty or fifty feet below the surface, and pumped air through it. Just as he had expected, the line of air bubbles produced exactly the same effect as the submerged reef. They set up a vertical current of water which broke up the waves as soon as they struck this barrier of air.

The "pneumatic breakwater," as it is called, has been tried out on an exposed part of the California coast, to protect a long pier used by an oil company. It has proved so satisfactory that the same company has now constructed a second breakwater about another pier near by. There is no reason why a breakwater of this sort should not be made about a wreck to protect the workers from storms. Where the water is very deep, it would not be necessary to lay the compressed-air pipe on the bottom, but it could be carried by buoys at a convenient depth.

Summing up the situation, then, there are two serious bars to the successful salvage of ships sunk in the open sea--the wild fury of the waves on the surface; and the silent, remorseless pressure of the deep. The former is the more to be feared; and if the waves really can be calmed, considerably more than half the problem is solved. As for the pressure of the sea, it can be overcome, as we have seen, either by the use of special submarine mechanisms, or of man-operated manikins or even of unarmored divers. We have reached a very interesting stage in the science of salvage, with the promise of important developments. Fifty fathoms no longer seems a hopeless depth.

Even in times of peace the sea exacts a dreadful toll of lives and property. Before the war the annual loss by shipwreck around the British Isles alone was estimated at forty-five million dollars. But the war, although it was frightfully destructive to shipping, may in the long run save more vessels than it sank; for it has given us sound-detectors which should remove the danger of collisions in foggy weather, and the wireless compass, which should keep ships from running off the course and on the rocks. And now, if salvage engineering develops as it should, the sea will be made to give up not only much of the wealth it swallowed during the war, but also many of the rich cargoes of gold and silver it has been hoarding since the days of the Spanish galleon.

INDEX

Air, fighting waves, 334 raising ship, on, 319 war in, 123

Airplane, ambulance, 146 armored, 139 artillery-spotting, 131 camera, 173 cartridges, 131 classes of work, 127 fighting among clouds, 137 flying boats, 144 gasolene tank, 130 giant, 132 hospital, 146 launching from ship, 303 Liberty motor, 142 scouting, 125 scouts, 128 speed of, 134 spotting, 177 training spotters, 180 wireless telephone, 194 See also Seaplane

Ambulance airplane, 146

Armored diving-suit, 330

Arms and armor, 111

Artillery, hand, 23

Atmosphere, shooting beyond, 64

Audion, 185

Balloon, Blimp, 260 helium, 164 historical, 148 hydrogen, 150

Balloon, kite, 174 principles, 150 record flight, 65

Barbed wire, 15 cylinders, 17 gate, trench, 9 gates through, 15 shelling, 16

Barge for towing seaplanes, 302

Barrage, grenade, 27 mine, 292

Battle-fields, miniature, 180

Blimp, 260

Blisters on ships, 307

Boats, electric, 308 Eagle, 301 flying, 144 surface, 298

Bombs to destroy barbed wire, 16

Breakwater, pneumatic, 335

Browning, John M., 56

Buildings, shadowless, 227

Caisson disease, 325

Caliber, 68

Camera, airplane, 173

Camouflage and camoufleurs, 211 buildings, 227 grass, 229 horse, 223 land, 222 roads, 225

Camouflage, ships, 211

Cartridges, aircraft guns, 131

Catapults, 36

Caterpillar tractor, 109

Caves, 8

Coffer-dam, salvage, 318

Color, analyzing, 229 screens, 229

Compass, wireless, 201

Convoy, 267

Countermines, 17

Deep sea, conditions in, 312

Deep water diving, 327

Depth bombs, 265

Devil's eggs, 276

Diesel engine, 240

Direction-finder, 205

Dirigible, see Balloon

Disease, caisson, 325

Diver, armored suit, 330 caisson disease, 325 rest chamber, 328 sled, 330 submarine torch, 329 suit, 324

Diving, deep, 324 record depth, 327

Duck-boards, 9

Dugouts, 7

Dummy heads of papier mâché, 13

Eagle boats, 301

Egg-laying submarines, 287

Eggs, Devil's, 276

Electric motor-boat, 308

Engine, Diesel, 240

Field-guns, 81

Fire broom, 105 liquid, 103

Forts, machine-gun, 58

Fuse, grenade, 28

Gas, 85 American, 102

Gas attack, boomerang, 92 first, 89

Gas, chlorine, 87 diphosgene, 96 exterminating rats, 94 grenades, 26 helium, 164 hydrogen, 150 lock, 97 masks, 99 mustard, 98 phosgene, 93 pouring like water, 86 shell, 95 sneezing, 98 tear, 95 vomiting, 98

Gasolene-tank, airplane, 130

Gate, barbed wire, trench, 9

Gates through barbed wire, 15

Gatling gun, 43

Geologists, Messines Ridge, 19

Glass, non-shattering, 100

Grapnel shell, 16

Graveyard, submarine, 314

Grenade, disk-shaped, 33 fuse, 28 gas, 26 hair brush, 34 history of, 23 Mills, 29 parachute, 31 range of, 25 rifle, 28 throwing implement, 27

Grenade, wind-vane safety device, 32

Gun, aircraft, 131 American, 50-mile, 63 big, hiding, 226 caliber, 68 disappearing, 77 double-end, 145 18-inch, monitors, 306 elastic, 73 field, 81 42-centimeter, 79 how made, 76 120-mile, 70 long range, German, 62 non-recoil, 145 on submarine, 249 16-inch, coast defense, 78 Skoda, 81 spotting by sound, 181 three-second life, 73 12-inch, submarine, 251 ways of increasing range, 67 wire-wound, 76

Hand-grenade, see Grenade

Helium, 164

Hospital, airplane, 147

Horizon, seeing beyond, 219

Howitzer, 79

Hush ships, 304

Hydroaëroplanes, see Seaplanes

Hydrogen, weight of, 150

Hydrophone, 270

Illusions, optical, 215

Kilometer, length in miles, 6

Kite balloons, 174

Kite, water, 283

Liberty motor, 142

Liquid-fire, 103

Locomotives, gasolene, 10

_Lusitania_, 316

Machine-gun, 112 airplane, 127 Benèt-Mercié, 52 Browning, 53 Colt, 44 forts, 58 Gatling, 43 history, 41 Hotchkiss, 49 Lewis, 50 Maxim, 42 water-jacket, 47 worth in rifles, 58

Machine-rifle, 55

Magnets, lifting, salvage, 334

Maps, making with camera, 175

Marne, first battle of, 4

Messines Ridge, mine, 19

Metal-cutting under water, 329

Microphone detectors, mines, 18

Mine-field, North Sea, 290

Mine laying, North Sea, 292

Mine-laying submarine, 287

Mine railroad, 294

Mine-sweeping, 281

Mines, 276 anchored, 278 and counter-mines, 17 automatic sounding, 278 drift of, 285 electric, 277 floating, 284 Messines Ridge, 19

Mines, paravanes, 288

Monitors, 306

Mortars, 79 depth bomb, 266 flying, 23

Mortars, See also Trench mortars

Mother-ships for airplanes, 305

Motor-boat, electric, 308 sea Tank, 299

Motor torpedo-boats, 298

Mystery ships, 220

Net, North Sea, 290

Ocean currents, 285

Optical illusions, 215

Oxy-hydrogen torch, submarine, 329

Paint in war, 209

Papier mâché heads, 13

Papier mâché horse, 223

Parachute, 175 grenade, 31 search-light shell, 84

Paravanes, 288

Periscope, submarine, 244 trench, 11

Pill-boxes, 59

Pneumatic breakwater, 335

Pontoons, salvage, 320

Propeller, shooting through, 136

Radio, see Wireless

Railroad, mine, 294

Railways, trench, 10

Range-finder, 170

Range, getting the, 169

Range of guns, increasing, 67

Range, torpedo, 213

Rats, freeing trenches of, 94

Rifle grenade, 28 safety device, 32

Rifle, machine, 55

Rifle stand, fixed, 14

Roads, camouflage, 225

Salvage, 310 diving, 324 ice-tongs, 334 lifting-magnets, 334 methods, 317 pneumatic, 319 pontoons, 320 shackles on ships, 333 submarine F-4, 321 submarine sphere, 332

Scouts, airplane, 128

Sea, deep, conditions, 312

Sea gulls finding submarines, 258

Sea lions locating submarines, 259

Sea tank, 299

Seaplane, 143 automatic, 145 submarine patrol, 259 torpedo, 145 towing-barges, 302

Search-light shell, 84

Shackles, salvage, 333

Shadowless buildings, 227

Shell, gas, 95 grapnel, 16 search-light, 84 shrapnel, 83 Stokes mortar, 39

Shield on wheels, 114

Ships, airplane, 304

Ships, blisters, 307 camouflage, 211 "clothes-line," 220 convoy, 267 hush, 304 making visible, 230 monitors, 306 mystery, 220 railroads on, 294 sunk by submarines, 310

Ships, see also Salvage

Shrapnel shell, 83

Sled, submarine, 330

Smoke screen, 262

Sniper, locating, 13

Sniperscopes, 12

Sound, detecting submarines, 269

Sound detectors, mines, 18

Sound, spotting by, 181

Sphere, salvor's submarine, 332

Spotting by sound, 181

Spotting gun-fire, 177

Submarine, blindness, 244 chasers, 255 construction, 234 depth bombs, 265 egg-laying, 287 engines, 246 F-4, salving, 321 getting best of, 253 graveyard, 314 guns on, 249 history, 232 hydrophone, 270 mine-field, 290 mine-laying, 287 net, 290 oil-tank, 236 periscope, 244 reclaiming victims of, 310 rest chamber, 328 salvage vessel, 332 sea-gulls, 258 sea-lions, 259 seaplanes, 259 ships sunk, 310 sled, 330 steam-driven, 250 torch, 329 torpedo, 246 12-inch gun, 251 vs. submarine, 269

Super-guns, 62

Tank, 107 American, 122 flying, 139 French, 119 German, 120 one-man, 114 sea, 299 small, 121

Telegraphy, rapid, 199

Telephone, New York to San Francisco, 186 wireless, 178

_Titanic_, 314

TNT (trinitrotoluol), 18

Torch, submarine, 329

Torpedo, 299 boats, motor, 298 electrically steered, 308 construction, 246 getting range, 213 proof ships, 306 seaplane, 145

Towing-barge, seaplane, 302

Trajectory, 22

Trench, gas-lock, 97

Trench mortar, 36 pneumatic, 37 Stokes, 38

Trench railways, 10

Trench warfare, 4

Trenches, 21 barbed wire gates, 9 duck-boards, 9

Tunnels, mines, 17 to observation posts, 12

U-boats, see Submarines

Villages, underground, 7

Walking-machine, 108

War, paint, 209

Water kites, 283

Waves, fighting with air, 334

Wireless compass, 201 spy detector, 200

Wireless telegraph, rapid, 199

Wireless telegraphy explained, 188

Wireless telephone, 178 airplane, 184

Wireless telephony across Atlantic, 192

Woolworth Building, falling from, 135

Wrecks, see Salvage

Zeppelin and Lowe's balloon, 149

Zeppelin balloon, construction, 156

Zeppelin, suspended observer, 162

Zeppelin's failures and successes, 154

* * * * * *

Transcribers' note:

Punctuation and spelling were made consistent when a predominant preference was found in this book; otherwise they were not changed.

Simple typographical errors were corrected; occasional unbalanced quotation marks retained.

Ambiguous hyphens at the ends of lines were retained.

Some illustrations have been slightly repositioned to improve their appearance in eBooks.

Page 76: "eight tenths of an inch" may be a misprint for "eight ten-thousandths of an inch".

Page 100: "inhaled air" was misprinted as "inhaled aid".

Page 104: "would send the stream" was misprinted as "sent".

Page 113: "Secretely" was printed that way.

Page 209: "psycologists" was printed that way.