the modern submarine torpedo-boat

the submarine torpedo-boat is to most people a complete mystery, and before describing the composition and strength of the submarine fleets at war it may therefore be of interest to say something of the principal features common to all types of submarine craft.

method of submergence

it may sound ridiculous, in face of the many accidents which have occurred, to say that one of the greatest difficulties is to make a submarine sink sufficiently quickly, and one of the easiest of operations to make her rise, and yet such is undeniably the case.[1]

41it will be readily understood that any delay in disappearing beneath the surface when attacking would be a great danger to a submarine in action. for example, a number of hostile torpedo-boat destroyers are scouring the sea in advance of a fleet, and are discovered at daybreak by the submarines, which are waiting to attack the fleet behind, approaching at a speed of 30 knots an hour. a hurried dive beneath the surface is necessary if the waiting submarines would avoid detection, which would, in all probability, mean destruction by the quick-firing guns of the destroyers.

when a submarine is travelling on the surface she is in what is technically called the light condition, that is to say, with her water ballast tanks empty, but when it is required to sink her so that only the tiny platform, or deck, and conning-tower are above the surface, water is let into these ballast tanks, and the additional weight causes her to sink into the sea until her 42back is almost flush with the surface—this is known as the awash condition.

it is not difficult to perceive that when travelling awash, a wave might at any moment roll along the tiny unprotected deck of the submarine, break over the mouth of the conning-tower, and descend like a waterspout into the interior. were this to happen a terrible disaster might result, for it must be remembered that when travelling awash, a very little additional weight would cause the submarine to plunge beneath the surface. in order to obviate this risk it has become a rule that when proceeding with this small margin of buoyancy, the hatch covering the mouth of the conning-tower should be screwed down and the submarine hermetically closed, ready to sink.

to many it may appear strange that total submergence is not accomplished by letting still more water into the ballast tanks, but entirely with the aid of the propellers and rudders. a submarine 43has two, and sometimes three, pairs of rudders; one pair of ordinary vertical ones to guide her to port or starboard, and a horizontal pair to cause her to dive and rise. two additional fins are frequently placed on each side of the forepart of the vessel to assist the diving and rising.

in order to make the submarine dive beneath the surface, the horizontal rudders are deflected when the boat is proceeding at full speed. the action of the water against the rudders is such that the bows are forced down and the whole vessel slides under the surface. the principle is much the same as that of steering an ordinary surface vessel, where the force of the water against the rudder causes the vessel to swing to right or left.

from this it will be seen that a submarine is only held below the surface by the action of her rudders on the passing water; should the propellers driving her along cease to revolve and 44the vessel slow down, she automatically rises to the surface because the rudders have no longer any effect.

although the steering both on the vertical and horizontal plane is controlled by hand, it would be quite beyond the strength of a man to move the various rudders as required, so electric motors are installed to perform the actual work. in fact, almost everything in a submarine is operated by electricity.

in the earlier types of submarine boats, a considerable time was required to open the valves and allow sufficient water to enter the ballast tanks to make them sink to the awash condition. some of the now obsolete french naval boats took as long as fifteen to twenty minutes to carry out this simple operation. the main reason for this was, that they were designed with too much surface buoyancy, that is to say, they rode too high in the water when floating in the light condition compared with the inadequate means then employed for the 45inlet of water into the ballast tanks, and were thus forced to let in an enormous quantity of water at a very slow rate before they settled down sufficiently to enable total submergence to be accomplished by the use of the horizontal fins and rudders. this great drawback has now been completely overcome, and the modern submarine can sink below the surface in about three minutes.

when water is pumped into the ballast tanks in order to make the submarine settle down, the air which normally fills these tanks is compressed into a fraction of its proper space, and is therefore always exerting a downward pressure which increases as more water is pumped in. therefore, when it is desired to bring the submarine to the surface again, all that is necessary is to open the valves and allow the compressed air to force the water out. it should, however, be remembered that there is really no need to “blow out” the ballast tanks in order to bring the submarine to the 46surface, for this can be much quicker accomplished by simply elevating the horizontal rudders; but in this case the submarine only rises just above the surface—to the awash condition—whereas if the tanks are emptied of water she rises to the light or cruising condition. this substantiates the assertion made at the beginning of this chapter—that it is far more difficult to make a submarine sink than it is to make her rise.

it has been said that a man walking from one end of a submarine to the other would, in all probability, cause her to plunge dangerously, so delicate is the state of equipoise when totally submerged. whatever may have been the case in the early types it is certainly not so now. so steady are modern submarines when running below the surface, especially those of the british, russian, french, and japanese and german navies, that the long up and down hill glides, which, with some boats, used to amount to yaws of from 20 to 30 feet, have now 47been reduced to a few feet in so many hundreds of yards. in fact, this switch-back motion is almost unnoticeable except when the submarine is being swung round at a sharp angle. in no case, however, is it sufficient materially to affect the firing of the torpedoes.

the reserve buoyancy of a submarine in the awash condition—or diving-trim, as it is called in the british flotillas—is necessarily very small, amounting to little more than two or three pounds in a thousand, which in a 300-ton vessel means a difference of only about 100 gallons of sea-water between the ability to float and the inevitability of sinking. any material increase in the small margin of what is known as positive-buoyancy must be accompanied by a corresponding increase in the power of propulsion, otherwise it would be quite impossible to drive her under, or, in other words, to overcome the vessel’s natural tendency to float on the surface.

for these and other reasons, a submarine 48when running submerged is in such a delicate state of equipoise that any sudden increase or loss of weight would upset the balance and so cause the vessel to either dive or rise with dangerous rapidity.

this would be the effect produced when a torpedo was discharged were provision not made to counter-balance this sudden loss of weight by means of compensating-tanks, into which sufficient water is pumped to compensate for the loss of weight incurred by the discharge of each torpedo.

many submarines are also fitted with bow and stern trimming-tanks, into which water can be pumped in such a manner as to correct any tendency of the vessel to float too high or low at either extremity.

propulsion.

of the many complicated problems surrounding submarine boat construction the motive power and propelling engines 49have been in the past, and are still, the most profound puzzles. steam, compressed air, electricity, petrol, and heavy oil have all been used with varying results since first this type of vessel came into being; and many curious engines for using these prime movers in conjunction with each other and with chemical compounds have been evolved by ingenious inventors.

about steam and compressed air little need be said, for although given a good trial, especially by the french naval authorities, they were abandoned some years ago in favour of a combination of petrol and electric engines, which in turn have given place to more powerful machines using heavy oil and electricity. steam is, however, again being used in conjunction with turbine engines for surface propulsion.

the carrying of large quantities of petrol, or heavy oil, is under all circumstances attended with a certain amount of risk, and when many tons 50have to be carried in a confined space, as in a submarine, this risk is more than doubled, as the slightest leakage when the vessel is submerged would mean that a powerful explosive mixture of petrol and air would be made.

a modern submarine torpedo-boat (british type). a. deck superstructure. b. scuppers for filling superstructure. d. external connections. e. conning-tower (4-inch armour). f. periscope. g. periscope motor (for turning, &c.). h. air cowls. i. conning-tower cap (opening sideways). j. mast stays. k. mast (not part of service equipment). l. torpedo-tube cap. m. torpedo-tubes (twin), torpedoes in. n. air-flask (for expelling torpedoes). o. hydroplane engines. x. double casing, with special vent for accumulators. y. spare torpedoes. z. petrol storage tanks (2). 1. air flasks. 2. centrifugal pumps. 3. air-lock, with submarine escape dresses. 4. commander’s platform. 5. ladders. 6. depth and deflection indicator, registering submarine’s deflection from horizontal. 7. speed dials. 9. petrol engines. 10. electric engines. 11. dynamo, for recharging batteries. 12. petrol engines—exhaust.

it being also quite impossible, for obvious reasons, to use a petrol engine 51when running submerged, a second motive power, an engine, with its additional space and weight, has to be carried to drive the submarine when under water. for this purpose electricity is used in almost all types. but electricity, again, has many drawbacks. it costs in weight nearly thirty times more than other motive powers, and is extremely dangerous, for should salt water in any way gain access to the storage batteries, chlorine gas would be given off in large quantities, although in the more recent vessels of the british, american, and french navies this danger has been minimised by enclosing the batteries in air-tight cases. on account of the weight and the space required, it is impossible to install a very powerful electric engine in a submarine (compared with the size of the boat), and thus both the speed and radius of action are curtailed.

if this division of power between the surface and submerged engines could 52be overcome, and the whole space made available for one powerful set of engines suitable for driving the vessel both on the surface and when submerged, not only would the mechanism of submarines be simplified, but a very considerable increase in both speed and range of action would naturally result.

in the “d,” “e” and “f” classes of british submarines, and in the more modern vessels of the french, russian and german navies, heavy oil is being used in place of petrol on account of the increase in power obtained with greater safety.

arrangements are made in almost all modern submarines so that when the vessel is using the oil engines for running on the surface the electricity for use when submerged is being made by a dynamo and stored in batteries. from this it will be seen that there are really three separate engines in a submarine:—(1) the oil or petrol motor, which drives the vessel when on the surface, and, at 53the same time, by a suitable arrangement of gearing, operates a dynamo, (2) which makes the electric current for storage, and (3) an electric engine which drives the vessel when submerged, obtaining the necessary power from the batteries.

it is, however, technically incorrect to say that there are two sources of power in a submarine, for electricity is not, in itself, a source of power, but merely a handy method of storing and transmitting it. the only actual source being the oil or petrol.

there are also numerous small engines to add to the complexity of machinery in a submarine, such as the air compressors used for charging the torpedo tubes with compressed air for expelling the torpedoes and for other purposes, and electric motors for operating the pumps, steering mechanism, and periscopes. in addition to all this, hand-mechanism is provided for use in case of a breakdown to operate most of these 54important appliances. then again there is, of course, the armament mechanism for working the torpedo tubes and semi-automatic quick-firing guns.

from the foregoing it may appear that the interior of a submarine presents a picture of mechanical complexity utterly incomprehensible. yet such is not the case. the fanciful belief that the crew stand, boxed up in these vessels, sweating with the heat, struggling for breath, and with crank-shafts whirling uncomfortably close to the small of their backs, electric motors buzzing within a few inches of their ears, and nervous hands grasping one or other of the levers ranged in rows in front of them, is, doubtless, most romantic, but quite unreal. much of the undoubtedly complicated machinery in a submarine is tucked away in the conical extremities, under the interior decking, and fixed to the arched steel sides. the centre is left almost entirely clear, so that trestle-tables may be erected for meals, 55hammocks swung for sleeping, and sufficient space allowed to make these small vessels as habitable as possible. not the least difficulty of the submarine designer is to create order and leave space among the chaos of machinery which has to be installed in these peculiar and deadly little torpedo craft.

vision when submerged.

perhaps the greatest difficulty which has beset both submarine construction and navigation is the puzzle how to see when submerged. this is now accomplished by means of periscopes, or tubes extending up from the roof of the submarine to a height of several feet above the surface—not unlike hollow masts. by a series of lenses and reflectors a picture of the surface is thrown down these tubes on to reflectors inside the submarine. a man with his eyes at the bottom of a periscope can see the surface clearly. although it projects above the surface when the whole submarine is submerged, 56it is far too small an object to be easily seen moving through the water, and extremely difficult to hit by gun-fire.

the latest panoramic periscope—two of which are fitted in modern submarines—has a field of vision of about 60 degrees. the range of vision is, however, very short, owing to the periscopic tube projecting only a few feet above the surface. on a moderately smooth and fairly clear day steering by periscope is not altogether difficult, but at night or in fog this instrument is useless, and for this reason it would be almost impossible for a submarine to effect a submerged attack on an enemy at night. hence the name given to this type of craft—daylight torpedo-boats—for in the brilliant light of day, when any attempt by ordinary torpedo craft to get sufficiently close to hostile warships to discharge a torpedo with reasonable hope of success would be foredoomed to failure, there is every possibility that submarines would effect a surprise attack.

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armament.

the chief armament of all naval submarines is the torpedo, which is expelled by a blast of compressed air from one of the tubes fitted in the bow and stern. several torpedoes are usually carried by each boat, so that if one failed to strike the object of attack further attempts can be made.

about the efficiency of torpedoes nothing need be said here, for they now form an important weapon in every navy, and to this subject a future chapter is devoted.

the latest submarines built are also fitted with quick-firing guns for use when these vessels are cruising on the surface. the guns are arranged so that when it is desired to sink they can be made to disappear beneath the narrow deck of the submarine. the provision of guns has been made with the object of giving these vessels a means of defence should they be discovered by prowling hostile torpedo-boat destroyers, or by air-craft.

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habitability.

many people imagine the interior of a submarine to resemble a stokehold, hot, stifling, and semi-dark, whereas the exact contrary is the truth. the temperature is but little above the normal for a ship’s engine-room, the air-supply is amply sufficient, and the whole interior is well illuminated by electric lamps.

the necessary supply of pure air is derived either from large steel cylinders containing the air in a highly compressed state or from flasks of oxylithe. the carbonic acid gas of the respired air being at the same time chemically absorbed.

food is cooked for the crew by electricity, and drinking water obtained from special tanks. notwithstanding these arrangements, however, it is almost impossible for the crew to live on board for many weeks at a time, owing to the small free space in the interior and to the cramped deck; but as the size and radius 59of action of these boats increase, so also does the space available for exercise, and thus the habitability.