Encyclopædia Britannica, Ninth Edition/Torpedo

by Edwin John Payne-Gallwey

TORPEDO.Torpedoes may be briefly described as charges of some explosive agent, enclosed in water-tight cases, and moored or propelled under water at such depths that by their explosion they may sink or seriously damage a vessel in their vicinity. The use of torpedoes in naval warfare was proposed and even attempted in the end of the last and beginning of the present century, but no successful application of them was made until the American Civil War of 1861-64. The word "submarine mine" is generally substituted for "torpedo" when speaking of defensive or stationary mines, the latter term being reserved for loco motive torpedoes, or others used in offensive operations.

1. Submarine Mines.—Submarine mines are divided into three classes: (1) observation mines, fired by an electric current when the enemy is observed to be within the destructive area of the mine; (2) electro-contact mines, which, when struck, fire by automatically completing the electric circuit from the battery ashore; (3) mechanical mines, which, when struck, fire through the action of some contrivance within themselves, and are not connected with the shore. Mines of the first class are used in places where a channel has to be kept clear for screw steamers to pass, the second class in those parts of the channel where there is little traffic, and the third class in channels which it is intended to bar equally against friend or foe.

Electrical mines have the advantage over mechanical that by the removal of the firing battery the passage of a ship is rendered perfectly safe, and that the condition of the mine can be ascertained by electrical tests, but the electric cables are liable to damage, and add greatly to the expense of the defence.

Gun-cotton and dynamite are the explosives generally used in mines, the charges varying from 30 ft to 500 ft, according to the description of mine. In all mines the charge is exploded by means of a detonator containing fulminate of mercury. In mines loaded with gun-cotton the detonator is inserted in a priming charge of dry gun-cotton, this priming charge being in a metal case, closely surrounded by the wet gun-cotton comprising the remainder of the charge. Where dynamite is employed the priming charge is not necessary. Experiments made to determine the horizontal distance at which an ironclad will be vitally injured by different charges have yielded the following general results:—

Charge. Submergence. Distance. 1 50 Ib mine 10 to 15 ft. 4 ft. 250 Ib ground mine 30 ft. 10 ft. 500 Ib ground mine 60 ft. 15 ft.

The explosion of 500 lb of gun-cotton at a horizontal distance of 30 feet would seriously injure a vessel, and 30 ft in contact with the bottom below the armour would probably blow a hole through the outer and inner skin. The depths given above are approximately the best depths to get the fullest effect out of the charges mentioned. When the water is so deep that if the mine were placed on the bottom it could not exert its full destructive effect on the bottom of a ship, it is given enough buoyancy to allow it to float above its moorings, a mine on the bottom being termed a "ground mine," and a mine floating above its moorings a "buoyant mine."

If mines are placed too close together the explosion of one will damage those near it, the interval which must be left between them being for a 100 ft mine, 100 feet; for a 250 ft mine, 250 feet; and for a 500 ft mine, 300 feet. There is therefore always a possibility of a ship passing through a single line of mines without coming within the destructive area of any. Mines are therefore generally arranged in two or more lines, the mines of one line covering the spaces left between the mines of the next, or several mines may be laid close together, and the whole exploded simultaneously.

The electric circuit of all electrical mines is very similar. A voltaic battery ashore has one pole put permanently to earth and the other pole joined to the electric cable leading to the mine. This cable passes into the mine case through a water-tight joint, and is connected up to one pole of the electric detonator, the other pole of the detonator being connected to the mouth-piece of the mine and consequently to earth. To prevent the mine being fired until the proper moment has arrived, this circuit must be broken somewhere, and means provided for completing it when the mine is to be fired. In the case of observation mines this is done by inserting a firing key in the electric cable near the battery, and in electro-contact mines by a circuit closer in the mine.

Observation mines.The right moment to fire an observation mine is determined by two observers ashore, who have each adjusted two sights in line with the mine, as it was lowered into position,—the stations for these observers being chosen so that their lines of sight may be as nearly as possible at right angles to each other. The electric cable from the mine is led past both observers and connected to a firing battery, one pole of which is put permanently to earth. A firing key inserted in the circuit at the station of each observer renders the simultaneous pressure of both keys necessary to explode the mine. If each observer depresses his firing key as the centre of the enemy crosses his own line of sight, both keys can only be pressed simultaneously if the enemy arrives at the intersection of the two lines of sight, and consequently over the mine. When many mines are placed in one channel, it is usual to moor them in three lines, the prolongation of each line converging to an observing station, where the direction of each line is marked by bights. The electric cables from all the mines come to another observing station, and are there connected to separate firing keys, each of which has one pole joined up to a firing battery. The observer at this station is also provided with a separate sight marking the direction of each mine in all the lines. The former station is termed the "converging" and the latter the "firing" station. The observer at the converging station telegraphs to the firing station the instant at which the centre of the enemy is on one of the lines of mines, the observer at the firing station determining by means of his sights which individual mine the enemy is over, and he can fire it by pressing the corresponding key.

Instead of separate sights for each mine, observing arcs may be used. These instruments are furnished with a telescope, which can be constantly directed on the enemy, a bar attachment automatically closing the circuit when the direction of the enemy corresponds to a mine. The camera obscura has also been used for determining the position of an enemy in the mine field.

Electro-contact mines.Electro-contact mines are buoyant mines moored about 10 feet below the surface, and are in connexion with an electric battery ashore. They are arranged to explode on being struck by a passing ship, by means of an apparatus contained in the mine itself, called a circuit closer. Many different kinds of circuit closers are in use, but they all depend upon there being a break in the electric circuit while the circuit closer is at rest, the circuit closer completing the circuit when the mine receives a blow. That most commonly used (fig. 1) consists of a steel spindle a carrying a weight b on its upper end. This steel spindle carries an insulated brass ring c, to which the wire from the detonator d is attached, the other pole of the detonator being connected to the cable e leading to the electric battery.

Fig. 1.

On the mine being struck the inertia of the weight causes the steel rod to vibrate sufficiently to bring the insulated ring in contact with brass springs in connexion with the earth, thus completing the circuit of the electric battery through the detonators. Another form of circuit closer is a tube of mercury, which by splashing up when the mine is struck completes the electric circuit between two previously insulated points.

A single main cable from the battery may have several electro-contact mines attached to it; the expense of leading a separate wire from each mine to the battery is therefore avoided. If one mine was fired the broken end of its branch wire from the main cable would be left in the water, and on another mine being struck it would only receive a portion of the current, as the battery would be connected to earth through the broken branch. Each branch wire must therefore have a disconnector in circuit, clear of the explosion. The disconnector consists of a platinum wire fuse contained in a strong iron case, and the same current which fires the detonator in the mine fuses the platinum wire bridge of the disconnector, and the circuit to the broken branch remains insulated.

Mechanical mines.Mechanical mines, of which there are many different patterns, contain the means of ignition within themselves, and are unconnected with any apparatus ashore. They may be ignited by percussion, friction, chemical action, and electricity.

A simple form of mechanical mine has a heavy top, which, on being pushed off by a passing ship, either pulls out a pin and re leases a plunger, which is then forced by a powerful spring into a detonator, or a friction tube is fired when the weight falls on a line attached to it. Another form, known as Abel's mechanical exploder, consists of a glass tube containing sulphuric acid, and surrounded by chlorate of potash and sugar. The whole is contained in an india-rubber tube, which projects from the top of the mine, the lower end being in communication with the charge. "When struck, the india-rubber tube bends, and, the glass tube breaking, the sulphuric acid mixes with the chlorate of potash and sugar and inflames the charge.

Electro-mechanical mines.Electro-mechanical mines can be made by placing a voltaic battery inside the mine itself and joining it up to a fuse and circuit closer, the circuit closer completing the circuit when the mine is struck. Another form of electro-mechanical mine (fig. 2) has several projecting horns (a, a, a) of lead tubing.

Fig. 2.

Inside each horn is a glass tube containing bichromate of potash, and immediately under it a row of small zinc and carbon plates, b, in a containing cell. On any one of the lead horns being bent, the glass tube is broken, and the bichromate of potash drops into the cell, converting the arrangement into a voltaic battery, which, being already connected to the electric fuse c, fires the mine.

All mechanical and electro-mechanical mines are provided with some contrivance to guard against accidental explosion during the process of laying. In mechanical mines a safety pin can be with drawn after the mine is in position, or, in the case of Abel's exploder, the projecting tube is surrounded by iron segments which fall off when the mine is in position. In electro-mechanical mines two of the wires forming part of the circuit inside the mine may be brought through to the outside and kept apart till the mine is in position, these wires being long enough to allow of the operator retiring clear of the explosion before joining them up and rendering the mine dangerous.

Mechanical mines have the advantage over electrical that they require fewer trained men for their manipulation, are cheaper, and can be placed in position very rapidly. But no really efficient method has yet been devised that will ensure a mechanical mine, after it has been placed in position, being safely taken up again for examination or removal, nor can any tests be applied to ascertain if it remains in an efficient condition.

Counter-mining.All mines, especially those with electric cables attached, must be protected by gun fire or guard boats, as, if the mine field is un protected, they can be easily destroyed by countermining or creeping. Countermining is carried out by exploding a succession of charges in an enemy's mine field. Mines containing heavy charges would be used for the purpose, several of these mines being dropped in succession from a boat towed by a fast steamer, the whole line being exploded together as soon as the last mine had been dropped. Numerous experiments have proved that the explosion of a 500 lb mine will effectually destroy any mine within a radius of 100 feet; the countermines would therefore be dropped at double this distance apart, and the channel so cleared marked by buoys. Electric cables can also be caught and raised to the surface by grapnels; or the grapnel may have a case of explosive between its arms, so that, instead of raising the wire, it may be cut by firing the charge.

2. Locomotive Torpedoes.—Locomotive torpedoes are a numerous class, the principal being the Whitehead, Lay, Sims, Brennan, and Ericsson. The Whitehead is the only one which can be considered a well-developed naval weapon.

Whitehead torpedo.This torpedo (fig. 3) is made in different sizes, varying from 12 feet to 19 feet in length and from 12 to 15 inches in diameter; the cross section is circular, tapering to a point at each end.

Whitehead Torpedo.

Fig. 3.—Whitehead Torpedo.

It is capable of being so adjusted that on being discharged it will travel at any depth between 5 and 15 feet below the surface, and it will maintain this depth for its entire run. The torpedo travels at a uniform speed for the whole of its range, the speed and range varying for different patterns; the latest type has a speed of 21 knots for 600 yards. The torpedo can be set so that, in the event of its not striking the ship aimed at, it will stop at the end of its range and sink. For exercise it can be set to stop at any distance within the limits of its range, rise to the surface, and float. The torpedo is divided into several compartments. The foremost A contains a charge of from 30 to 100 lb of gun-cotton, according to the size of the torpedo. This charge is fired on the torpedo striking a ship by a pistol which screws into the nose of the torpedo. On impact the point of the pistol is driven inwards and forces the point of a steel striker into a detonator. By means of powerful air-pumps air is compressed into the air-chamber B to a pressure of 1000 lb on the square inch, and actuates a three-cylinder engine, which drives two propellers revolving in opposite directions in the tail. The mechanism in the balance-chamber C works two exterior rudders on each side of the tail, which keep the torpedo at a uniform depth during its run. This device has never been patented, but is a secret; the details of it, however, have been purchased by all prominent maritime nations.

The tail F is fitted with four broad fins, which tend to keep the torpedo on a straight course and prevent it rolling. The horizontal tail fins carry four rudders, two horizontal and two vertical. The horizontal rudders worked from the balance-chamber keep the torpedo at its set depth; the vertical rudders are permanently adjusted so as to cause the torpedo to travel in a straight line.

The air-chamber of a torpedo is usually made of fluid compressed steel, the remaining compartments of thin steel plate, and the interior mechanism of phosphor-bronze. In Germany torpedoes are now made entirely of phosphor-bronze.

The torpedo can be discharged from above or below Fig. 3. Whitehead Torpedo. water. From above water it is shot out of an air-gun (fig. 3) mounted on the deck of a ship and pointing through the side. The air-gun consists of a metal tube a, a, a, of the same length as the torpedo, the rear end being closed by an air-tight door. The gun carries a reservoir c of compressed air, the contents of which, by means of a suit able firing valve d, can be instantaneously admitted into the gun. When the torpedo is to be discharged this firing valve is opened, and the compressed air in the reservoir forces the torpedo out at a high velocity, a tripper 6 projecting through the top of the gun throwing back the starting lever of the torpedo on its way out. From below water the torpedo is discharged through a tube, the muzzle of which forms part of the stem of the ship, the tube being fitted with an outside valve which prevents the water from entering while the torpedo is placed in the tube. Latterly powder has been used instead of compressed air for the ejecting force.

Lay torpedo.The Lay torpedo is a boat of cylindrical form, the fore part being charged with an explosive. The motive power is carbonic acid gas generated in the usual way. As only a very small portion of the boat is visible on the surface, two guide rods, one on each end of the vessel, mark its position at any part of its run. The boat can be started, stopped, and steered by means of an electric cable, containing several insulated wires, which is paid out from the boat as it travels.

Sims torpedo.The Sims torpedo is cigar-shaped, and is suspended to a boat-shaped float. The torpedo is propelled by screws driven by an electric motor situated in the body, the current for which is supplied from a dynamo ashore. The electric cable is coiled on a drum in the torpedo, and pays out as the torpedo advances. The torpedo is also steered from the shore by an electric current. Its speed is about 12 knots.

Brennan torpedo.The principle of the Brennan torpedo is as follows. The torpedo contains two drums upon which a large amount of pianoforte wire is wound. One end of the wire from each drum is taken to large drums ashore, which are revolved by a steam-engine. By winding up on the large drums ashore a rotatory motion is imparted to the drums in the torpedo, which by means of gearing revolve two screw propellers, and these drive the torpedo through the water. The torpedo can be steered from the shore in any direction, by winding on one drum faster than the other, which alteration in motion moves a vertical rudder on the torpedo.

Ericsson torpedo.The Ericsson torpedo is a long fish-shaped weapon, made of wood, and weighted so as to have little or no buoyancy. The charge is contained in a metal case at the fore end. It is propelled by a charge of gunpowder, out of a submarine gun fixed in the bows of a ship. Its range is about 300 feet, and it fires on impact.

Outrigger, drifting, and towing torpedoes.Outrigger, Drifting, and Towing Torpedoes.—Before the introduction of the Whitehead, vessels armed with torpedoes were principally supplied with the outrigger torpedo. The explosive is contained in a metal case secured to the end of a steel or wooden pole, which lies fore and aft in the vessel carrying it. The pole can be rigged out until the torpedo is submerged a short distance ahead of the vessel, and is fired on contact with the enemy's side, either by an operator in the boat completing the electric circuit, or by the circuit being completed by a circuit closer in the torpedo. In rivers, or places with a current, drifting torpedoes can be used. They should be suspended from floats, and arranged in groups or pairs connected together by a rope, so that they may catch across the bows of a vessel at anchor. They can be fired after a given lapse of time by clockwork and other devices, or can be so arranged that the firing arrangement is released on a catch being withdrawn by the action of a propeller wheel, which remains stationary as long as the torpedo drifts with the current, but is revolved by the force of the current when the torpedo is stopped. Towing torpedoes are constructed to diverge from either side of a ship when towed, which is effected by shaping the torpedo like an otter. The torpedo tows on the surface, and, on striking a ship's side, the head containing the charge drops off, and fires as its weight tautens a line connecting it to the body.

Torpedo boats.Torpedo Boats. The great improvements made of late years in machine guns have rendered the outrigger and towing torpedo of little value for torpedo boats, as it would be almost impossible to approach a vessel near enough to use them before the boat would be destroyed by the storm of missiles which would be fired at her. All torpedo boats under construction, and most of those already completed, are therefore armed with the Whitehead torpedo. A modern torpedo boat is built entirely of steel, the plates often not exceeding 1/16 inch in thickness, as, in order to get the necessary high speed, the minimum of weight consistent with the necessary strength is of the first importance. There are three classes of boats, known as first, second, and third. The first are capable of keeping the sea on their own account; the second are for harbour defence; and the third can be carried on board a ship.

The following table gives the dimensions and other details of a boat of each type:—

Type of Boat. Length. Beam. Dis placement. Full Speed in Knots. Indicated Horse Power at Full Speed. Boiler Pressure, Ib per Square Inch. Distance Boat can steam with Coal carried at Full Speed. Half Speed. 1st class.. 2 it class... 3d class... Ft. 135 86 64 Ft. in. 13 11 7 6 Tons. 88 30 12-5 23 20 16-5 1150 450 150 140 125 120 Knots. 400 150 100 Knots. 2000 400 250

The boilers and machinery are protected by coal, and an armoured tower protects the steering gear and telegraphs for controlling the engines.

Torpedo nets.Torpedo Nets.—The introduction of the modern torpedo boat has caused great attention to be paid to any means which will protect a ship from the torpedo. Host nations are adopting steel-wire netting, suspended from booms attached to the ship's side, the booms keeping the nets sufficiently far off to prevent any damage being done to the bottom by the explosion of the largest charge carried by a Whitehead. This netting, besides being cumbersome and heavy, cannot be used unless the ship is stationary or nearly so, so that in many cases it would be useless, but for ships at anchor it is of great value. Increased cellular subdivision is also being given to ships under construction, and special vessels, called "torpedo catchers," are being built by most nations. A torpedo catcher is a vessel of superior size and strength, but with the same high speed as a torpedo boat, the principal arm of the torpedo catcher being machine guns. (E. P. G.)