CHAPTER IV

THE MECHANISM OF THE SUBMARINE, AND SUBMARINES OF THE FUTURE

Mr. H. G. Wells, in his “Anticipations,” confesses that his imagination, in spite even of spurring, refuses to see any sort of submarine doing anything but suffocate its crew and founder at sea. “It must involve physical inconvenience of the most demoralising sort simply to be in one for any length of time.... You may of course throw out a torpedo or so with as much chance of hitting vitally as you would have if you were blindfolded, turned round three times and told to fire revolver-shots at a charging elephant.... Given a derelict ironclad on a still night within sight of land, a carefully handled submarine might succeed in groping its way to it and destroying it; but then it would be much better to attack such a vessel and capture it boldly with a few desperate men on a tug. At the utmost, the submarine will be used in narrow waters, in rivers, or to fluster or destroy ships in harbour, or with poor-spirited crews—that is to say, it will simply be an added power in the hands of the nation that is predominant at sea. And even then, it can be merely destructive, while a sane and high-spirited fighter will always be dissatisfied if, with an undisputable superiority of force, he fails to take.”

We are afraid that Mr. Wells has not taken the trouble to keep himself in touch with the latest developments of submarine navigation. As we write, news comes from America of a party who spent fifteen hours under water in the _Fulton_ without suffering any inconvenience. This does not look much like the “suffocation” Mr. Wells anticipates. As to torpedo-firing, French and American boats whilst under way have made excellent practice, both at stationary and at moving targets; while in making the assertion that the submarine will be used in narrow waters, in rivers or in harbours, it is evident that Mr. Wells is unaware of the lengthy voyages made by some of the newest boats.

The _David_ represented the best type of under-water vessel in the sixties; that she is infinitely inferior to the newest _Holland_ type or some of the French vessels of to-day goes without saying, and it will not be surprising if the submarine of thirty years hence bears the same resemblance to the _Holland_, as the _Holland_ does to the _David_.

The ideal submarine boat has a speed as great as that of the fastest torpedo-boat, a very wide radius of action, excellent sea-keeping powers, unlimited quantities of air for power and for respiration by the crew; a means of directing its course by vision upon a moving object whilst itself remaining invisible beneath the surface, and is very habitable and comfortable for long periods of time.

The submarine of to-day lacks most of these attributes. It has a slow rate of speed, whether on the surface or submerged, a narrow radius of action, poor sea-keeping powers, a strictly limited quantity of compressed air, and is absolutely blind when beneath the waves. Thus it differs greatly from the ideal boat as sketched above, but its gradual improvement may be safely predicted.

We propose in this chapter to describe, in simple language, the working of a vessel intended for under-water navigation, and to consider what improvements are likely to take place.

Every submarine boat worked by a crew must of necessity be capable of floating on the surface of the water. This is a self-evident proposition, for the crew must have means of ingress and egress, and the only practical way of entering and leaving the boat is by an opening in the hull when she is on the surface.

We have no doubt that the files of the Patent Office would show that many inventors had designed boats which would sink to a certain depth directly they were placed in the water. While in such a system no time is lost in submersion, there would undeniably be difficulties in the way of coming to the surface, &c.

The first problem, then, which confronts the designer of a submarine boat is to find the most suitable method of sinking it to the depth at which it is intended to navigate.

The most fundamental law of hydrostatics, which applies to all floating bodies, and is equally true of wholly submerged vessels floating at any depth, as of ships of ordinary form, floating on the surface, having only a portion of their volume immersed, is that a ship floating freely and at rest in still water must displace a volume of water having a weight equal to her own weight.

The “displacement” of a vessel is defined as the weight of water displaced, which is equal to the weight of the vessel and that of her lading. A ship floating on the surface “displaces” a certain weight of water; in order to force her beneath the surface two methods are open.

In the first place, her weight is increased by the introduction of water ballast; thus her “displacement” is altered and she sinks until her weight is again equal to the volume of water displaced.

In the second, the weight of the boat remains constant, but the displacement is altered by the drawing in of “cylinders” or “drums;” thus she sinks until her displacement again equals her weight.

The first inventor to employ the latter method was André Constantin, who built a vessel during the siege of Paris, which was furnished with pistons working in two cylinders; on these being drawn in from the interior the boat sank to the required depth. The actual trials were, however, not satisfactory. The _Nautilus_, of Messrs. Campbell & Ash, which underwent some trials in Tilbury Docks in 1888, depended also on the pulling in of cylinders (ten were employed, five on each side of the vessel), for her submersion; the results were equally discouraging, and some eminent men nearly lost their lives owing to the erratic behaviour of this craft.

No serious ship-constructor would nowadays think of adopting this method of submersion, and we may therefore pass on to consider those which are brought to the submerged condition by the admission of water into special reservoirs or tanks.

Submarine boats so far as their immersion is concerned may be divided into two classes.

1. Those which when submerged possess no floatability.

2. Those which in the same condition possess a small reserve buoyancy or floatability.

Modern submarines almost without exception belong to the second division, as this class has been found to possess great advantages over the first.

1. SUBMARINES WITH NO FLOATABILITY WHEN SUBMERGED.

Boats belonging to this division possess when submerged a total weight equal to the weight of water displaced. During immersion it has been found necessary to make the weight of the vessel and its contents slightly exceed the weight of water displaced by the total volume of the vessel; this excess of weight causes a downward motion which rapidly accelerates unless checked, and care must be taken to regulate, either automatically or otherwise, the depth, lest the vessel sink to a depth where the pressure is greater than she can withstand.

Although M. Goubet is a believer in the “no-floatability” idea, it has, for some time past, been regarded with disfavour. Theoretically it is possible to navigate a submarine whose total weight equals the weight of water displaced so that she keeps at a given level without rising or sinking, but the system will not work satisfactorily when put to severe and prolonged tests. It is found to be impossible to obtain perfect equality between the two weights: submarine currents, variations of atmospheric pressure and temperature, and movements inside the boat all tending to disturb its equilibrium.

2. SUBMARINES POSSESSING FLOATABILITY WHEN SUBMERGED.

Mr. Nordenfelt realised the superiority of submarines possessing a reserve buoyancy when submerged over those which possessed no buoyancy and all the most important of latter-day submarines fall under this division.

It is quite obvious that should any accident happen, such as the entry of water, the failure of the machinery, the asphyxiation of the crew (rendering the detaching of a false keel impossible), &c., the submarine with a reserve buoyancy would at once rise to the surface, while the boat with no floatability would remain where it was and then gradually commence to sink, owing to the fact that it is almost impossible to prevent the water from finding its way, little by little, into the boat.

Submarines which possess floatability when submerged have a weight which is less than their displacement and some mechanical action must be resorted to to force them below the surface. The first operation consists in introducing a certain amount of water into the tanks so that the boat is brought to the “awash” condition, with the greater part of the hull below water and only the conning tower, &c., appearing above the waves. The complete submersion of the vessel may be attained in two ways: either screws on vertical shafts are employed to “screw” the vessel below the surface, whether at rest or whilst moving; or horizontal rudders, or planes, are used to steer the boat below the surface; this latter method is only applicable to moving vessels.[3]

Footnote 3:

A system of moving weights was employed by Drzewiecki and other inventors.

IMMERSION BY SCREWS MOUNTED ON A VERTICAL SHAFT.

Just as a ship is driven backwards and forwards in the horizontal plane by means of a screw or screws mounted on a horizontal shaft, so it is possible to drive a ship up and down the vertical plane by means of one or more screws immersed in the water and mounted on a vertical shaft; the boat is by this method literally “screwed down” into the liquid.

The principle of the vertical screw was adopted by Bushnell who, in the description of his submarine vessel, writes: “At the top there was likewise an oar for ascending and descending or continuing at any particular depth.... When the skilful operator had obtained an equilibrium (by means of the forcing pumps) he could row upwards and downwards or continue at any particular depth with an oar placed near the top of the vessel, formed upon the principle of the screw, the axis of the oar entering the vessel. By turning the oar one way he raised the vessel, by turning it in the other he depressed it.”

M. Gaget remarks that “it is very strange that Bushnell should have discovered and concealed with so much care the instrument of propulsion which Sauvage studied and introduced fifty years later.” The fact is, of course, that the principle of the screw-propeller was known in the seventeenth century and that in May, 1785, Joseph Bramah patented a screw-propeller, identical in general arrangement with those in use to-day. The first practical use of the screw was made by John Stevens, who in 1804 launched a steamboat eighteen feet long by fourteen feet beam with a direct acting high-pressure engine having a tubular boiler—and driving a screw with four blades. Although the principle of the screw for ship propulsion was thus recognised at this early period it was not till the thirties (of the nineteenth century) that the screw-propeller succeeded in attracting the attention of the engineering world.

Professor Tuck in his boat (1884) placed the propeller directly beneath the centre of the hull, so that it should submerge on an even keel.

Mr. Nordenfelt used vertical screws, which at first he fitted in side sponsons, but afterwards in the fore and aft line, and considered it absolutely essential that a diving boat should be kept horizontal when being submerged, as any inclination downwards with the impetus of a heavy boat would, he considered, almost to a certainty carry the boat below its safe depth, before it could be effectually counteracted by shifting weights. Such a theory was soon shown to be founded on a misapprehension.

Some inventors (Waddington, Baker, &c.) have used four screws operating in pits equidistant from the centre of the boat, two on the upper part and two on the under part, but all such methods have been discarded in the newest designs.

IMMERSION BY HORIZONTAL RUDDERS.

The ordinary vertical rudder steers the ship either to port or starboard in the horizontal plane, and the horizontal rudder can be used similarly to control its position in the vertical plane.

This method of steering a boat beneath the surface by the inclination of horizontal rudders is, of course, only applicable when the boat is moving.

The position that the horizontal rudder or rudders should occupy is a question about which much has been written, and opinion appears to be still divided on the subject. Some hold that they should be placed at the stern, others that they should be placed on either side of the vessel, and these latter again differ as to whether they should be forward, amidship, or aft. In spite of all the arguments in favour of placing the rudders forward, Captain Hovgaard considers that this disposition can hardly be recommended except in very long boats where it may prove a necessity. The _Gustave Zédé_ has six diving rudders, two forward, two in the centre, and two aft; whilst in the _Narval_ class there are four rudders, two forward and two aft; the _Holland_ submarines have aft rudders only.

_Control in the Vertical Plane._

That beautiful machine, the Whitehead torpedo, is maintained at a set depth below the surface by means of a pendulum and a hydrostatic valve which regulate the horizontal rudders, and also in its true course by the gyroscope. In the case of the submarine it is necessary that it should not pass a certain limit when on its downward course, and that it keep so far as is possible the same level throughout its run under water.

The control of the submarine in the vertical plane may be accomplished by the manipulation of the rudders, either automatically, by means of some such arrangement as the hydrostatic valve or pendulum, or by hand, and she can be kept on an even keel and prevented from rising to the surface or sinking to the bottom, when running beneath the waves, by the pumping of water from a reservoir situated aft to one situated forward, or vice versâ, by the admission of water into trimming tanks, by shifting weights, &c. These operations can be carried out either automatically or by hand-operated mechanism.

It will be readily understood that while it is a comparatively simple matter to force a vessel beneath the surface to a depth previously determined, it is not so easy to ensure its keeping at this depth during the whole time it is submerged and maintaining throughout the run a perfectly even keel.

One of the greatest difficulties the inventor of submarine boats has to overcome is their lack of longitudinal stability. Submerged vessels are of two classes, those which are equal in weight to the water they displace, and those which are lighter. Both classes are subject to various disturbances which tend to upset their longitudinal stability and send them up to the surface and down towards the bottom. In Chapter XV. mention is made of the difficulties experienced by those who had to navigate the Nordenfelt.

The principal causes of disturbance have been summed up by Captain Hovgaard in a paper entitled, “The Motion of Submarine Boats in the Vertical Plane,” read before the Institution of Naval Architects at the Annual Meeting in 1901.

1. Faulty use of horizontal rudder. 2. Admission of water through leakages. 3. Expulsion of foul air and products of combustion. 3a. Firing of torpedoes and projectiles. 4. Movements of crew. 5. Existence of free surfaces of liquid. 6. Movements of loose weights, such as fuel. 7. Variations of buoyancy caused by varying density of sea water. 8. Grounding and collision. 9. Variations in speed.

Some of the most important of these disturbances may be briefly discussed.

1. Most modern submarines are provided with more than one pair of horizontal rudders, but if all the rudders should refuse to act and the boat is running down an inclined plane, the only thing to be done is to pump the water out of the tanks and thus bring the boat to the surface.

2. By the careful construction of the hull, and by strict control of all sea-valves, the admission of water may be prevented. If the boat is stove in and water enters in any quantity, she will inevitably sink. As an escape some inventors have provided their submarines with detachable boats.

3. Usually the length of the run under water will not be so great that the foul air will need to be got rid of. If necessary it can be expelled by drawing on the store of compressed air, and as the substances withdrawn will always be small, no change in longitudinal balance need be feared if precautions are taken. As all modern submarines are driven by electricity beneath the surface, the expulsion of products of combustion need not be considered.

3a. In the earliest submarine boats the torpedoes consisted of charges of explosive in cases, which were attached to the outside of the vessel to be attacked, or were towed against her sides.

Those who had little faith in the future of under-water warfare declared that a torpedo could never be fired from a tube in a submerged vessel without disastrous effects. The Nordenfelt boats were certainly not successful in discharging torpedoes, for as a general rule they as nearly as possible stood up vertically on their tails and proceeded to plunge to the bottom stern first on these occasions.

However, since then, submarines have fired torpedoes quite satisfactorily under water.

The expulsion of a torpedo from a vessel totally submerged in the water, whether equal to or less than the weight to the water displaced, naturally reduces her weight and tends to send her up towards the surface. This tendency can best be counteracted by the admission of a certain quantity of water ballast into the boat.

The method now usually followed is to allow the surrounding water to enter the tube immediately after the launch of the torpedo, and as the weight of the volume of water admitted will be about equal to that of the missile ejected, the longitudinal stability of the submarine should not be disturbed. When the second torpedo comes to be placed in the tube, the volume of water already in it must of necessity be ejected, and a compensating reservoir may be used to receive it. As each torpedo is fired a certain amount of water, corresponding to the weight of the projectile, must be allowed to enter the compensating reservoir. This may be done automatically.

The _Engineer_ in a leader on January 18, 1901, said: “The discharge of a bow torpedo (by a submarine) would be instantly followed by the rise of the bow; relieved of the weight the boat would tend to stand on end. If going ahead at the time she would immediately come to the surface to be destroyed. If going astern she would plunge downwards and the consequences might be equally serious.... Torpedoes must be fired when the submarine is at rest.”

In spite of this dogma submarines have fired torpedoes whilst in motion with success, and in modern submarines ample provision is made for the loss of weight occasioned by the discharge of the torpedo.

4. Reference has been made to the fact that when the Nordenfelt boat was moving along on an even keel, and a greaser walked forward a couple of feet in his engine room, her head would go down a little, the water would surge forward in the tanks, and she would plunge to the bottom, unless checked in time. It has been said that one man going forward in a submarine boat would cause her to dive to a depth of thirty-six feet in one minute. The movements of the crew may be compensated for by automatic arrangements, but the ideal method would be one in which every one remained immovable at his post during the submerged run.

_Steering Below Water._

Quite early in the history of submarine navigation it was found that the compass was not so reliable when the boat was navigating under water as it was when she was on the surface. This is not to be wondered at, for the compass of a submarine is placed in the interior of a tightly-closed metallic shell and in close proximity to an electro-motor and powerful currents capable of influencing it considerably, if not of rendering it altogether useless.

The principal causes of the unreliability of the compass on a submerged boat are:—

1. The currents normally produced by the electric motor.

2. The abnormal currents flowing in certain unknown parts of the hull owing to lack of proper insulation.

3. The permanent or transitory magnetisation of the hull if made of a magnetic metal.

The best position for the compass on a submarine has been a much debated point, but it is now generally agreed to be in the centre of the hull. The conning tower of the first British submarine was made of steel, but it was afterwards replaced by one of brass.

M. M. Gaget in his book[4] states that so entirely untrustworthy and impracticable has steering by compass in French submarines been found, that the gyroscope has been requisitioned. He inclines to the belief that this instrument is the best indicator of route that has yet been devised, yet he points out the want of some reliable method by which the distance made by a submerged boat could be gauged with accuracy.

Footnote 4:

“La Navigation Sous-Marin.”

MOTIVE POWER.

The question of the best method of propulsion for submarine boats must be considered under two heads, namely, propulsion on the surface and below the water.

It will be quite evident that the conditions under which a motor in a submarine works differ according as the boat is running above or beneath the surface; and we arrive at the conclusion that if the same motor is to serve for both conditions special arrangements will have to be made to permit it to work under abnormal conditions. Should this be found impracticable a new method of propulsion will have to be found for under-water travelling.

Every heat engine consumes both air and fuel (whether coal, oil, gas, &c.), and the process of absorption of the fuel is accompanied by the giving out of a certain weight of the substance in the form of gas. Whilst the boat is proceeding beneath the water its weight is continually being modified, and it is practically impossible to compensate for this change by the addition of water to the reservoirs. Besides this difficulty the combustion of the fuel not only absorbs a large quantity of the air which is so precious a quantity in a submerged vessel, but also sets free deleterious gases which naturally have prejudicial effects on the health of the crew. It may therefore be asserted that a submarine can only be propelled under water by means of a motor capable of working without combustion or loss of weight. It remains therefore to discover the most suitable method fulfilling these conditions.

1. _By Mechanical Means such as Clockwork, Springs, &c._—The Howell torpedo is driven by means of a heavy flywheel in the interior which is spun up to 10,000 revolutions a minute before discharging by means of special machinery. While all these methods are practicable they must be put aside as unsuitable owing to the slowness of the speed which a boat thus propelled can attain.

2. _Compressed Air._—In order that a submarine may be driven at a high rate of speed for a considerable distance, such a large store of compressed air would have to be carried if this method were adopted, that little space would be left in the vessel for any other purposes. In addition to this such a store of compressed air would be a source of danger.

3. _Manual Power._—The earliest submarines were of course driven by hand power, but no one nowadays would think of adopting this method.

4. _Steam from Heated Water._—Mr. Nordenfelt propelled his boats beneath the surface by means of the steam given off by the heated water in the cisterns, and this was found sufficient for a distance run of 14 knots. He disliked accumulators, and this is not to be wondered at, for in his time they were very far from perfect; were he designing a submarine to-day, however, it is probable that he would choose electricity for sub-surface working.

5. _Chemical Engines._—Dr. Payerne, d’Allest, and others, by means of a _chaudière pyrotechnique_, burnt, in hermetically closed furnaces, combustibles containing in themselves the oxygen necessary for their combustion, and got rid of the products of combustion by ingenious devices.

6. _Electricity._—All modern submarines rely on an electric motor for under-water propulsion, the current being derived from accumulators. The ideal primary battery and the ideal accumulator are still to seek, but the latter improves yearly, and there is little doubt that some few years hence the current available will enable the submarine to make long voyages under water with greatly increased speed. It is said that the _Holland_ has on no fewer than four occasions burned up the armature of her motor, and some device seems to be wanted to keep the armature cool.

7. _Carbonic Acid._—Many attempts have been made to construct an engine which can be worked by liquid carbonic acid, but the general result, as some one has said, has hitherto been that the inventors have been more or less broken up in body and mind.

8. _Liquid Air_ has been suggested as a propelling agent for submarines, but up till now it has not been applied for such a purpose. A motor-car propelled by liquid atmospheric air was shown at the Agricultural Hall in April last, and some energetic Americans are endeavouring to “boom” this elusive substance in this country. More sober investigators have, however, little faith in an immediate commercial future for liquid air.

PROPULSION OF THE SURFACE.

While the “Holland” boats for the British and United States navies are driven on the surface by a gasoline engine, this type of motor has not yet been used on the French boats, a steam engine fed with liquid fuel being employed in the _Narval_ and vessels of this class, while in the _Gustave Zédé_, _Morse_, &c., electricity is the sole motive power both above and below the waves. _Le Yacht_ states that France has always avoided the use of gasoline owing to the danger which arises from its presence on board submarine craft.

(_a_) _The Steam Engine._—In the Nordenfelt boat steam was raised, when running on the surface, by the burning of coal, but of late the advances that have been made by the employment of liquid fuel have led to the employment of this combustible for submarine boat propulsion in preference to coal.

The great drawback at present to the use of the steam engine is the length of time necessary for the unshipping of the chimney, the cooling of the engines, &c.

(_b_) _The Oil Engine._—At the present time there is no oil motor in existence of sufficient power to give even moderate speed to a large boat, but the ingenuity of the engineer will probably overcome this drawback.

Those who make the dogmatic assertion that the submarine boat cannot be very fast because she cannot be endowed with much power, remind one of the wiseacres who were so convinced that steamboats would never replace sailing-vessels, nor steam locomotives the horse-drawn coach.

“The power required to impel a vessel through the water is augmented by her submergence. If 5,000 1–h.p. are required to drive a displacement of 120 tons at 28 knots, then rather more power will be required to drive 120 tons wholly submerged at the same speed.”

This statement appeared in the _Engineer_ in the early part of 1901, but it appears that an exactly opposite opinion is held by many eminent authorities. For instance, at the discussion which followed the reading of Mr. Nordenfelt’s paper on Submarine Boats at the Royal United Service Institution in 1886, Mr. Anderson, C.E., stated that it was well known through the late Mr. Froude’s investigation that a fish-shaped vessel under water was in much more favourable circumstances for obtaining high speed than any vessel on the surface of the water, because it had been established theoretically that a vessel of easy lines completely submarine met with no resistance at all except the skin friction of the water, no resistance, that was to say, such as that which arose from the bow wave.

Mr. Anderson went on to say that he believed that if Mr. Nordenfelt would apply a little more ingenuity and perseverance to the perfecting of his boat, the result would be the attainment of a very high speed under water, and consequently a most formidable vessel. Mr. Nordenfelt himself said that it was absolutely proved that the speed below for a given consumption of fuel for a given boat must be greater than the speed above, and Mr. J. J. Thornycroft recently explained to an interviewer that the resistance is less for a completely submerged body than one travelling on the surface, because no waves are created. “The water that is displaced in front,” he said, “simply closes in behind and helps to push the body forward. A boat moving on the surface throws out waves in front and on either side, and that means an absolute loss of energy. You will find that for this reason a ‘Whitehead’ torpedo travels faster under the water than on the surface.”[5]

Footnote 5:

_Daily Graphic_, November 10, 1900.

ARMAMENT.

The armament of the boats designed by Bushnell and Fulton was a case of explosive; the armament of the _David_ that sank the _Housatonic_ was a spar-torpedo, but the armament of all modern submarines is the automobile fish torpedo. Mr. Holland in his earlier designs provided his boats with guns, but submarine cannon firing heavy shells have since been discarded.

In the new British submarines one torpedo expulsion tube is fitted at the extreme forward end of the vessel, opening outward 2 feet below the light water-line. Five Whitehead torpedoes, each 11 feet 8 inches long, are carried.

SAFETY AND HABITABILITY.

It may safely be said that no difficulty will be found in getting sailors to form the crew of a submarine boat in time of war. Great Britain, the United States, France, and other great naval Powers have only to call, and hundreds of brave fellows will volunteer, however great the odds against which they may have to fight. This being the case, our naval constructors must see to it that every precaution is taken to make the boats as safe and as habitable as possible.

The accidents to which a submarine is subject are many. The most serious is passing the safe limit of depth. If she descends beneath this limit the pressure will increase; her hull will be battered in; she will diminish in volume; her downward course will be rapidly accentuated, and there must inevitably follow the crushing in of the boat and the death of the crew.

For every boat there is a limiting depth, beyond which she must not go. While it is quite possible to construct a boat strong enough to resist the pressure at depths of 50 fathoms and over, it will not be necessary to go deeper than 5 to 6 fathoms, or enough to clear the keel of a big ship. Still it will be well to give the boat a hull capable of resisting pressures greater than those she will normally encounter. By means of a hydrostatic valve or some similar arrangement, the submarine may be kept from diving to too great depths.

It is said that the “Goubet” boats can withstand the pressure at a depth of about 5,000 feet, or very nearly a mile beneath the surface; the “Holland” boats can navigate with safety at 150 feet, a depth quite sufficient for all practical purposes.

The French submersible _Silure_ was recently sunk to a depth of 134½ feet, and it was found that the hull was compressed to the extent of 1–25th of an inch. No inconvenience was felt by the crew greater than that experienced at a depth of 20 feet.

Submarines possessing floatability have the power of rising to the surface should any accident happen to the motive power, steering gear, machinery, &c., and automatic arrangements are provided for working the horizontal rudders in order to keep the boat on an even keel. Some accident might, however, cause the boat to begin to sink, and the advisability of the submarine carrying a false bottom or detachable keel has been pointed out, as this could be dropped in an emergency, causing the vessel to rise at once to the surface.

The vessel _Le Plongeur_ carried a detachable boat, and Captain Hovgaard in his design also supplied such a boat. It was made to stand the same pressure as the submarine itself, and rested on a saddle-shaped packing, against which it was tightly pressed down by means of a number of clips. Inside the packing was a circular door in the boat and a corresponding and smaller one in the ship arranged in such a way that it was possible to get up into the boat, close the lower lid in the ship, and then the lid in the boat. This done, all the handles of the clips were turned and the water would probably enter the space inside the packing, and if not it might be made to do so through a small pipe leading from the outside to the space, and provided with a stopcock. The boat would now have a certain buoyancy, but would hang on in two main clips, placed one at each end of the detachable boat on mechanical connection with each other so that they could only be let go both at the same time, thereby preventing jamming. When these clips were opened the boat would ascend to the surface; communication with the vessel, if somebody should be left behind, might be kept up by telephonic connection.

M. Goubet, M. Drzewiecki, and other inventors provided their vessels with means for being propelled by the crew, working either oars or pedals, in the event of the machinery failing to act.

Respiration, or breathing, is a part of the life of all organisms, whether animal or vegetable. Air is taken into the lungs; the oxygen is absorbed, while the carbonic acid is given back again to the atmosphere. The respiration of human beings or animals in closed chambers to which the air is denied access is not possible beyond a certain period. The oxygen is sooner or later, according to the size of the chamber, used up, and the air becomes so vitiated with the carbonic acid expelled by the lungs that the vital functions of the body are arrested.

Many of the earlier submarine boats carried no reserve of air, as the time that they were intended to remain under water was not long.

Reference is made in old writings to the “chymicall liquor” supposed to have been used by Cornelius Drebbel to restore the purity of the air in his under-water vessel, but what its composition was we shall never know.

The air required for respiration in a submarine vessel may be supplied in two ways.

1. By some chemical method which purifies and regenerates the vitiated air.

2. By compressed air or oxygen carried in special reservoirs.

3. By pipes leading down from the surface to the submerged vessel through which fresh air is drawn and the foul air expelled.

4. By the return of the boat to the surface and the taking in of a fresh supply of air.

Such substances as caustic soda, lime, bromide of magnesium, &c., are capable of absorbing carbonic acid, and have been used, but modern submarine vessels rely on compressed-air compartments. M. Calmette, in his account of his voyage under water in the _Morse_, says that thanks to the labours of a commission formed by M. de Lanessan the difficulty of respiration has been satisfactorily overcome, with the result that the crew can remain for sixteen hours under water without the slightest strain. This may refer to the discovery by M. Georges Jaubert of a chemical substance of comparatively light weight which in one single operation can not only completely remove from vitiated air the carbonic acid, water vapour, and other non-respirable products, but can also automatically restore to it in exchange the exact mathematical quantity of oxygen which it lacks. In other words the substance when placed in contact with air vitiated by respiration can completely regenerate it and restore to it its original qualities. This wonderful substance, the composition of which has not yet been made public, has been the subject of some communications by Dr. Laborde to the Paris Academy of Sciences. In these it is mentioned that experiments were being made under the auspices of the Minister of Marine, and that these had proved that with 3 to 4 kilos of this new product it was possible for a man to live for twenty-four hours in an hermetically closed chamber.

VISION WHEN SUBMERGED.

When completely submerged the submarine boat is practically blind, and it is impossible to steer it by direct vision through the water. However slow its course the steersman would be unable to stop it before an obstacle which rose suddenly into the restricted circle of his aquatic vision, and he is therefore obliged to steer his course by means of bearings taken before descending.

At one time inventors believed that some light would come down through the water to help the steersman, but it is now acknowledged that once below the surface the boat is in impenetrable darkness. Some have proposed the use of a powerful electric projector which would emit a beam of light sufficient to light up a path 50 to 60 metres long in front of the submarine.

Unfortunately such an arrangement is not possible in practice. In the first place, such a projector would be of great size and weight and would require a considerable amount of current, but even if it were installed on a submarine it would be of no use to those on board for the reason that they would be placed immediately behind it and would be able to distinguish nothing owing to the great glare. The projector’s light would also be likely to betray the position of the submarine owing to the rays finding their way to the surface.

A submarine boat when navigating as an ordinary torpedo-boat on the surface or in the “awash” condition can be steered from a cupola or conning tower fitted with windows, which is affixed to the top of the hull, and which remains above the water when the hull is below.

It was asserted that such a cupola would not only be of no use beneath the waves, but would also be a disturbing element in the equilibrium of the boat, reducing its speed. For this reason the _Gymnote_ and the _Gustave Zédé_ were provided with telescopic domes capable of being pushed up or down at will. The arrangement was very complicated, and did not give good results, so it was abandoned, and all modern submarines carry a fixed dome on their deck platform.

When the submarine is submerged to a depth not greater than 10 to 12 feet such aids to vision as the optical tube and the periscope may be employed, but when the depth exceeds this limit the helmsman must rely on his compass, coming from time to time to the surface to verify, and, if necessary, rectify his route.

The periscope (from the Greek περι, around, and σκοπειν, look) is applied to an instrument by which objects in a horizontal view may be seen through a vertical tube. It may be said to consist of a vertical tube with a lenticular total-reflection prism at the top by which horizontal rays are projected downward through the tube and brought to a focus, after which they are received by a lens, the principal focus of which coincides with that point. The vertical cylindrical beam thus formed is converted into a horizontal one again by a mirror inclined at 45° from the vertical axis of the tube, and is thus conveyed to an eyepiece through which, by turning the tube on its vertical axis with its attached prism, a view of all the supernatant objects around the vessel may be obtained. A screen or diaphragm operated by a tangent screw is used to cut off the view of the vertical plane in which the sun is. When used on a submarine boat the top of the periscope floats on the surface.

The optical tube with which the _Gustave Zédé_ was at first provided before she carried a periscope consisted of a lens and a prism on the top of a tube, and the image of the surface was thrown on to a surface of paper. By the aid of the picture on the sheet of white paper the steersman could, under certain circumstances, tell approximately where he was going.

A writer in a recent number of the _Debats_ has something to say about vision below water.

“We certainly possess these vessels capable of navigating under water, which is no small advantage, but in order that they may be able to fight under these conditions and become really effective fighting machines the question of vision will have to be perfectly solved. The _Moniteur de la Marine_ affirms that the periscope, the apparatus intended to secure this power of vision, perfectly fulfils its object. It gives, six metres under water, a good enough view of what is going on upon the surface to enable a boat to steer towards the enemy’s vessel without the necessity of rising to the surface to make observations which quick-firing guns would render dangerous. No less an assertion than this is necessary to shake certain doubts on this point which will be shared by all who have been in a position to observe the troubles caused to the vision by the water and vapour on ground glasses. Only those who have used this instrument have the right to say with Polycente, ‘Je vois, je sais, je crois, je suis illuminé.’

“We who have not seen cannot go so far as this. It is also necessary that the images given by the periscope should be susceptible of rapid measurement, sufficiently accurate for the officer in command to be able to know if he is near enough for his torpedo to prove effective.

“In a word, the _Sous-Marin_ and the _Submersible_ are at present marvels of applied mechanics. They will be fighting machines only when the problems of vision and accurate measurement of distances are fully solved. If this result is reached we shall not long be kept in the dark, for with modern parliamentary methods all over the world we shall witness the simultaneous appearance in all naval budgets of demands for considerable sums in order to construct these vessels.”

A device for submarine vision, termed the cleptoscope, and invented by Messrs. Russo and Laurenti, is reported to be used on the Italian submarine _Delfino_. In its original form the instrument, according to the _Lega Navale_, gave an exact view in a closed chamber of all that was to be seen round about a submarine to any one applying his eye to a small eyepiece. In its later form it gives the same image much enlarged, and visible to both eyes at once at some distance from the chamber.

As an illustration of the disadvantages arising from the fact that the submarine is blind, the following story may be told, the accuracy of which cannot however be vouched for.

An Italian submarine went out on one occasion for practice. All at once the crew found that they could neither go ahead nor astern, nor could they rise to the surface. They pumped out the spare water that was provided to give additional buoyancy, but with no effect. The heavy lead keel provided for an emergency was at last detached; still the boat refused to rise, and the crew gave themselves up for lost.

The Port-guardship was riding in the anchorage, and fortunately her captain heard a scraping and knocking which could not be accounted for at the bottom of his ship. It occurred to him at last to signal to the station on shore asking if the submarine boat was out for practice, and on being told it was, he shifted his anchorage, whereupon the submarine boat came to the surface with a rush like a cork, and the crew were rescued in a very exhausted condition.

The optical instrument used on the new British submarines is termed the “Hyphydroscope,” and is the invention of Sir Howard Grubb, F.R.S.