THE MINE SWEEPERS

A mine is a torpedo that has no motive-power of its own but is either anchored or set adrift in the supposed path of an enemy’s ship. We have already seen how Bushnell used drifting mines at Philadelphia in 1777. Anchored mines are among the many inventions of Robert Fulton. The following description of the original type, illustrated by an engraving made by himself, is taken from Fulton’s “Torpedo War and Submarine Explosions.”

“Plate II represents the anchored torpedo, so arranged as to blow up a vessel which should run against it; B is a copper case two feet long, twelve inches diameter, capable of containing one hundred pounds of powder. A is a brass box, in which there is a lock similar to a common gun lock, with a barrel two inches long, to contain a musket charge of powder: the box, with the lock cocked and barrel charged, is screwed to the copper case B. H is a lever which has a communication to the lock inside of the box, and in its present state holds the lock cocked and ready to fire. C is a deal box filled with cork, and tied to the case B. The object of the cork is to render the torpedo about fifteen or twenty pounds specifically lighter than water, and give it a tendency to rise to the surface. It is held down to any given depth under water by a weight of fifty or sixty pounds as at F: there is also a small anchor G, to prevent a strong tide moving it from its position. With torpedoes prepared, and knowing the depth of water in all our bays and harbors, it is only necessary to fix the weight F at such a distance from the torpedo, as when thrown into the water, F will hold it ten, twelve, or fifteen feet below the surface at low water, it will then be more or less below the surface at high water, or at different times of the tide; but it should never be so deep as the usual draft of a frigate or ship-of-the-line. When anchored, it will, during the flood tide, stand in its present position; at slack water it will stand perpendicular to the weight F, as at D; during the ebb it will be at E. At ten feet under water the waves, in boisterous weather, would have little or no tendency to disturb the torpedo; for that if the hollow of a wave should sink ten feet below what would be the calm surface, the wave would run twenty feet high, which I believe is never the case in any of our bays and harbors. All the experience which I have on this kind of torpedo is, that in the month of October, 1805, I had one of them anchored nine feet under water, in the British Channel near Dover; the weather was severe, the waves ran high, it kept its position for twenty-four hours, and, when taken up, the powder was dry and the lock in good order. The torpedo thus anchored, it is obvious, that if a ship in sailing should strike the lever H, the explosion would be instantaneous, and she be immediately destroyed; hence, to defend our bays or harbors, let a hundred, or more if necessary, of these engines be anchored in the channel, as for example, the Narrows, to defend New York.

“The figure to the right of the plate is an end view of the torpedo. H-H shews its lever forked, to give the better chance of being struck.

“Having described this instrument in a way which I hope will be understood,” continues Fulton, “I may be permitted to put the following question to my reader, which is: Knowing that the explosion of one hundred pounds of powder, or more if required, under the bottom of a ship-of-the-line, would destroy her, and seeing, that if a ship in sailing should strike the lever of an anchored torpedo, she would be blown up, would he have the courage, or shall I say the temerity, to sail into a channel where one or more hundred of such engines were anchored? I rely on each gentleman’s sense of prudence and self-preservation, to answer this question to my satisfaction. Should the apprehension of danger become as strong on the minds of those who investigate this subject as it is on mine, we may reasonably conclude that the same regard to self-preservation will make an enemy cautious in approaching waters where such engines are placed; for however brave sailors may be, there is no danger so distressing to the mind of a seaman, or so calculated to destroy his confidence, as that which is invisible and instantaneous destruction.”

But Admiral Farragut at Mobile Bay, half a century later, did have the “temerity to sail into a channel where one or more hundred of such engines were anchored.” The monitor Tecumseh struck and exploded a mine that sent her to the bottom with almost her entire crew. The rest of the fleet began to waver when, from the main-rigging of the Hartford Farragut shouted his immortal command:

“Full steam ahead! Damn the torpedoes!”

As the flagship led the way through the mine-field, those on board heard mine after mine bump against her bottom, but though the levers were struck and the primers snapped, the powder-charges failed to explode. Hastily improvised out of beer-kegs and other receptacles, with tin or iron covers that became rusty and useless soon after they were placed under water, many of the Confederate mines were in this respect inferior to the well-built copper torpedoes of Fulton. Yet crude as they were, they destroyed more than forty Northern warships, transports, and supply vessels.

Percussion-caps instead of flintlocks were now used to explode contact mines. A new type of anchored torpedo, set off by an electric spark through a wire running to an operator on shore, was also a favorite with the Confederates. Because they are exploded not by contact with the ship’s hull but by the closing of the circuit by the operator when he observes an enemy’s vessel to be above one of them, these are called “observation mines.” In the Civil War, many effective mines of this sort were made out of whisky demijohns. One of these blew up the gunboat Cairo, in the Yazoo River, in the autumn of 1862. The double-ended, river gunboat Commodore Jones was blown to pieces by an observation mine, whose operator was subsequently captured and tied to the cut-water of another Federal gunboat as a warning and a hostage. During the bombardment of Fort Sumter by the United States fleet in 1863, the New Ironsides lay for an hour directly above an observation mine made of boiler iron and containing a ton of gunpowder but which failed to explode despite all the efforts of the operator. He was naturally accused of treachery and it would have gone hard with him had it not been discovered, soon after the New Ironsides ceased firing and stood out to sea, that the shore end of the wire had been severed by the wheel of an ammunition wagon.

During the Franco-Prussian War, the powerful French fleet blockaded the German coast but did not attack the shore batteries, which were well protected by mines. After peace was declared the foreign consuls at one of the North German seaports congratulated the burgomaster on having planted and taken up so many mines without a single accident. Unknown to any one, the prudent burgomaster had unloaded them first, and they kept the French away just as well.

In the Spanish-American War, Admiral Dewey was able to enter Manila Bay and destroy the Spanish squadron there because its commander “had repeatedly asked for torpedoes (mines) from Madrid, but had received none and his attempts to make them had been failures.”20 It was the mine-fields and not the feeble shore batteries that kept Sampson’s fleet out of Havana and Santiago. At Guantanamo, now a United States naval station, the Texas and the Marblehead each “struck her propeller against a contact mine, which failed to explode only because it was incrusted with a thick growth of barnacles. Gratitude for the vessels’ escape may fairly be divided between divine care to which the gallant and devout Captain Philip attributed it in his report, and the Spaniards’ neglect to maintain a proper inspection of these defenses. A number of these torpedoes, which were of French manufacture, and contained forty-six and a half kilograms (one hundred and two pounds) of guncotton, were afterward dragged up in the channel.”21

At the siege of Port Arthur in 1904, the Japanese fleet planted mines outside the harbor to keep the Russians in, and the Russians came out and planted mines of their own to entrap the blockaders. While engaged in this work, the Russian mine-layer Yenisei had a mine which had just been lowered through her specially constructed sternports thrown by a wave against her rudder, and was blown to atoms by the consequent explosion of three hundred more in her hold. The flagship Petropavlosk, returning from a sortie on April 13, struck a Japanese contact-mine and went down with the loss of six hundred men, including Vereshchagin, the famous painter of war-scenes, and Admiral Makaroff, who was not only the commander but the heart and soul of the Russian fleet.22 A month later, another mine cost the Japanese their finest battleship, the Hatsuse. Nor was the loss confined either to the belligerents or to the duration of the war. Nearly one hundred Chinese and other neutral merchant vessels were sunk by some of the many mines torn loose from their anchors by storms to drift, the least noticeable and most terrible of derelicts, over all the seas of the Far East, long after peace was declared.

The same thing on a larger scale will doubtless take place as a result of the present European War. From the Baltic to the Dardanelles, both sides have sown the waters thick with contact mines, hundreds of which have already broken loose and been cast up on the shores of Denmark, Holland, and other neutral lands. How many more have been picked up on the coasts of the different belligerent countries, the military censors have naturally kept a close secret; how many of these infernal machines are now drifting about the North Sea, the North Atlantic, and the Mediterranean it is impossible to compute. Scarcely a week passes without the publication of such news items as the following extracts from “Current events in Norway,” in the “American-Scandinavian Review” for July-August, 1915:

“One hundred and fifty mines had been brought into Bergen up to April 12. The steamer Caprivi of Bergen, which sank after being struck by a mine off the coast of Ireland, was on its way from Baltimore with a cargo of 4150 tons of grain, the property of the Norwegian government.... The German government has declared its willingness to comply with the demand of the Norwegian government for compensation for the Belridge, provided it be proved that the sinking of the steamer was the result of a German torpedo. The pieces of the shell found in the side of the vessel are to be sent to the German government, and in case there should be any disagreement about the facts they will be submitted to arbitration.”

Unfortunately in most cases where a neutral ship is so sunk, the exploding mine automatically destroys all evidence of its own origin, and each belligerent promptly and positively declares that it must have been planted, if not deliberately set adrift, by the other side. The neutral is left to get what satisfaction he can out of the ruling of the last Hague Conference that all contact mines must be so constructed as to become harmless after breaking loose from their moorings. There is nothing mechanically difficult about installing such a safety device, and all the great powers now at war with each other solemnly pledged themselves to do so. But the temptation of perhaps destroying a hostile battleship as the Hatsuse was destroyed, by a drifting mine, has apparently been too great.

Premature explosion of the mine during handling and planting, such as caused the destruction of the Yenisei is, of course, carefully guarded against. One of the simplest and most effective safety devices is that used in the British navy, where the external parts of the exploding apparatus are sealed with a thick layer of sugar, which is dissolved by the sea-water after being submerged for a few minutes. By then the mine-laying vessel has had time to get safely out of the neighborhood.

Modern mines are of various shapes and sizes but are as a rule either spherical or shaped like a pear with the stem down. The anchor is a hollow, flat-bottomed cylinder, containing its own anchor cable wound on a windlass, and making a convenient base or stand for the explosive chamber or mine proper, so that the whole apparatus can be stood or trundled about the deck of a mine-layer like a barrel. Once placed in the water either by being dropped through the overhanging stern-ports of a large sea-going mine-planter like the U.S.S. San Francisco, or lowered over the side of a smaller craft by a derrick boom, the weight of its anchor causes the mine to assume an upright position. This releases a small weight or plummet at the end of a short line attached to a spring that keeps the windlass inside the anchor from revolving. When the plummet has sunk to the end of its cord, its weight pulls down the spring, and the windlass begins to revolve and unreel the cable, the end of which is, of course, made fast to the bottom of the mine. This causes the anchor, which has been held up by the buoyancy of the mine, to sink, and follows the plummet till the latter touches the bottom. Freed of the plummet’s weight, the spring now flies up and stops the windlass. But the hollow anchor is now filled with water, whose additional weight drags the mine under. When the anchor rests on the bottom, the mine will be at the same distance beneath the surface of the water as the anchor had to sink after the windlass stopped, or the length of the plummet’s line. By regulating that, a mine can be made automatically to set itself at any desired depth.

Mines are almost never laid singly but in groups, the area of water so planted being called a “mine field.” A secret, zigzag channel is often left clear for the benefit of friendly craft. The rows of mines are usually “staggered” or placed like the men on a checker-board, so that if a hostile vessel passes through an opening in the first row she will strike a mine in the second. Another device is to couple together the mooring cables of two or more mines so that a ship passing between them will draw them in against her sides.

Contact may cause explosion in any one of several different ways. The head or sides of the mine may be studded with projecting rods like the striker on the nose of a Whitehead, to be either driven directly in against a detonating charge of fulminate or else open the jaws of a clutch and release the spring of a firing-pin. Such external movable parts, however, are too prone to become overgrown and clogged with barnacles and the like. A more modern way is to have the shock of the collision with the ship’s hull dislodge a heavy ball held in a cup inside the mine. The fall of this weight sets in motion machinery which fires the detonating charge. Or the device may not be mechanical but electrical, as in the type of mine that, when drawn far enough over to one side by a vessel passing over it, spills a cupful of mercury. This stream of liquid metal closes an electric circuit, so that an electric current passes through a piece of platinum wire embedded in fulminate and heats it red-hot, with obvious results. This current may be obtained either from a storage-battery carried in the mine itself, or through a wire running down the mooring cable and over the bottom to the shore. Most shore-control mines are so designed that they can either be fired by observation, or else turned into electro-contact mines of the above-mentioned type by arranging the switches in the controlling station. It is also possible to have the contact serve to warn the operator on shore by ringing a bell and indicating the position of the intruding ship in the mine-field.

Just as barbed-wire entanglements on land are blown out of the way by small charges of high explosives, so mined areas of the sea can be cleared by “counter-mining.” One or more strings of linked-together mines, of a small, easily-handled type, are carefully placed by light-draft vessels in the waters already planted by the enemy. When these are exploded together, the concussion is enough to destroy any anchored mines near at hand, either by setting off their exploding-devices or causing their cases to leak, so that they will be filled with water and sink harmlessly to the bottom. Or a channel may be cleared by “sweeping” it with a drag-rope towed along the bottom by two small steamers, exploding the mines or tearing them up by the roots. Very effective work of this kind has been done by the small steam-trawlers used by the North Sea fishermen, and if anything of the sort is ever necessary in American waters we may be thankful for the powerful sea-going tugs now towing strings of barges up and down our coasts.

But even a light field-piece on shore can shell and sink the sort of small, unarmored craft that must be used for mine-sweeping. When a fleet attacks a channel or harbor entrance properly defended by both mine-fields and batteries, each supporting the other, there comes a time when the naval forces must wait till troops can be landed to drive away the forces protecting the rear of the batteries, so that the mine-sweepers can advance and clear a channel for the superdreadnoughts. The most striking example of this is the holding of the Allied fleet by the Turks at the Dardanelles.

There, too, effective use is being made of the latest, which is an adaptation of the oldest type of torpedo: the drifting mine.23 This twentieth-century improvement on Bushnell’s “kegs charged with powder” floats upright, with a vertical-acting propeller on top and another on its bottom, and a hydrostatic valve set to maintain it at any desired depth. Should it rise or sink, the change in pressure will cause the valve to act on the principle already explained in connection with the Whitehead torpedo (see page 44). Controlled by the valve, the little compressed-air motor attached to the vertical propellers will cause them to make a few revolutions, just enough to keep the mine at a constant depth beneath the surface of the Dardanelles, as the four-mile-an-hour current carries it down against the Anglo-French fleet. Within a few hours of each other, during the furious bombardment of the forts on March 18, 1915, the French battleship Bouvet was struck by one of these drifting mines and went down stern-foremost, then H.M.S. Ocean was sunk by another, and the Irresistible forced to run ashore to escape sinking, only to be pounded to pieces by the guns of the forts. A feature of this type of mine is that its size and shape enable it to be launched through a torpedo tube, either from a surface craft or from a submarine.

Ordinary contact-mines, without anchors and attached to floats that held them a few feet below the surface of the water, are sometimes dropped overboard from a vessel closely pursued by an enemy. A small mine so dropped by a German light cruiser returning from an attempted raid on the English coast, early in the war, was struck by the pursuing British submarine D-5 and sent her to the bottom. The D-5 was running awash at the time and only two officers and two seamen were saved.