ONE of the most pressing problems at the present time is that of coping with the submarine menace. American inventors have turned to it with characteristic energy and many suggestions have been made, the best of which are summarized in the following article from The Scientific American.
All naval men are agreed that the best method of procedure against the submarine menace is to attack the U-boats at their bases; in other words, the ocean is expansive, and once a German submarine escapes to the open Sea the area over which the hunt must be conducted is such that the chances of capturing or destroying it are few. Indeed, it is the old case of an ounce of prevention being worth a pound of cure; but in this particular instance the proportion is somewhat altered —the ounce of prevention is readily worth a ton of cure. However, just so long as the submarines are permitted to roam the high 'heas the submarine problem resolves itself mto a matter of detecting and capturing or /destroying the U-boats; all of which stands ( for the ton of cure.
J Of paramount importance is the detection of the German U-boats, for once their presence is known they are robbed of their initi.nl.pnd greatest advance—invisibility. Naval men have told us time and again that given the location of a U-boat, the task of capturing or destroying it becomes almost automatic, or at least simple and practically certain. So the subject of detection is an important one and should receive the immediate and best attention of all inventors working on the submarine problem. To this end there has been collected a number of suggestions and principles which, after careful study, have either been held as having special promise or as entirely misleading with regard to the detection of U-boats, and this collection forms the basis of the present article.
Prominent among the suggestions offered by inventors is that of using some form of optical instrument, such as an inverted periscope, for seeing under water. When it comes to seeing any appreciable distance, say even a few hundred feet, the inverted periscope and other similar devices are practically valueless. Mr. Harold A. C. Sintzenich, a cinematographer who has exposed thousands of feet of film at the bottom of the sea by means
of the well-known W’illiamson tube, states that under the best conditions one cannot see mjre than 100 feet, and even then the objects are hazy masses devoid of detail. Beyond that distance -at a depth of 30 feet or more — everything blends into a dark green background. Now the point to bear in mind is that the Williamson apparatus permits a direct vision through a two-inch thickness of optically perfect glass, and there is a minimum of light absorption; and if 100 feet appears to be the extreme range of vision under ideal conditions, surely the distance would be considerably shorter when using any type of periscope. As the depth increases the vision
rapidly decreases, for sunligh : penetrates the water only in a very limite« way. Even with the aid of powerful lights it is impossible to increase the range óf vision, i ince there is no better illuminant than sunli ;ht to begin with. ^
The use of submarine searchlig its has been suggested for the purpose of detecting the Uboats, one plan being to employ a red beam of light which, according to the inventor, could be seen stretching out from the hull of the ship to a distance of several mil« ■ by an observer in the crow’s nest. The i ed beam, it is claimed, would form a more s riking contrast with the green water thi n a white one, hence it could be seen durit g «laylight. By means of a remote electrical control the observer could play the project >r around, watching all the while the thin pei cil of light some two miles in length. Sho ild g 'submarine be lurking in the vicinity t; f the ship, the beam of light would come in c« ntact with it, and obviously the pencil of ligh t would be interrupted at that point. The obs erver, not-ing that the pencil of light did not extend its normal distance, would immedia ely know that some object was interposed ir the beam at that point. With the angles of the sighting instrument and the projector k town, and working with a base line—the dii Unce between the sighting instrument ant; the projector of known length, the exact « ¡stance of the submarine from the ship could be accurately determined and communicati d to the gun crew. (
Unfortunately, however, it is qui * impossible to penetrate water for any f rent distance with light of any kind, da] light included. It may be true that red li| ht would serve to better advanUge because of the contrast with the green muss of matter; still, the fact remains that its penetrativ > power would be less than that of white li| ht. Experiments performed with a sUndan 30-inch projector indicate that 200 feet is tl e greatest distance that can be penetrated b; a ly concentrated beam, and needless distance is toUlty inadequate.
The electro-magnet has been the much interest in connection with marine detecting problem, and have been the suggestions to employ tism in some form or another, scheme is to lower electro-magnets water and tow them along, with
of having them attracted to the steel sides of any submarine they may encounter—a sort of magnetic fishing, as it were. Once the ' electro-magnets firmly hold on the submarine there are several procedures, depending upon the ideas of the individual inventor. Some advocate sliding a contact bomb down the wire cable connected to the electro-magnet, while others suggest lifting the submarine out of the water, capturing it intact and making its crew prisoners!
If persons interested in the electro-magnetic detector would spend a few minutes of their time experimenting with a permanent magnet, or, better still, an electro-magnet, they would soon learn the fallacy of this method. To begin with, magnetic lines of ‘force are curved, starting at one pole of the magnet and terminating at the other. For this reason magnetic force is very localized; as an example of this, suppose an electromagnet will lift ten pounds readily, it is bizarre indeed that the same magnet will not attract a small nail a few feet away. But such is the fact.
In consequence it becomes evident that fishing for submarines by means of electro-magnets is not w remunerative method, for the ocean is big and in order to detect the U-boat it is absolutely necessary to have the electromagnet come into actual contact with the steel mass. As for the holding power of the magnet when once in contact with the steel plates of the underwater prey, there is no doubt, since windings of any desired strength can readily be used; but the suggestion on the whole is so typical of honting a needle in a haystack that its application seems precluded from the very start.
It p magnet did possess the power of attracting large bodies at a distance, as most inventors evidently take for granted, this method would bold much promise. But unfortunately this is not the case, and we are unable to change the phenomenon of magnetism.
A variation of the electro-magnetic principle is the suggested use of a sensitive eompass to detect the presence of a great mass of steel, such as a submarine. However, it must be taken for granted that the device is to be employed aboard a wooden ship, which eliminates it from consideration where a steel vessel is concerned, thereby limiting its application to wooden cargo boats and small craft. While it is true that a compass needle is quite sensitive, it is doubtful if it would prove of much value in detecting a submarine hull a short distance away, even under ideal conditions.
Water, especially salt water, is a pretty fair conductor of electricity. Taking advantage of this fact at leaaTone inventor has suggested making use of electrodes arranged in the form of buoys or even using electricallyfired mines themselves, and measuring the resistance of the water between pairs by means of sensitive electrical instruments. Under normal conditions the resistance would not vary appreciably; but once a submarine pampd between the electrodes its huge bulk, several times that of the electrodes, would materially affect the resistance of the circuit, allowing more current to flow through and indicating a greater deflection on the galvanometers or other measuring instruments. All of which sounds most promising on paper.
However, salt water is such an excellent conductor of electricity that electrical engineers scoff at the practicability of this idea. They point out that the drop in resistance brought about by the passage of a submarine would be very small, even when the electrodes or mines were placed close together; and if the electrical instruments were made delicate enough to detect this slight drop in resistance, the slightest irregularity in the positioning of the electrodes and the thinnest layer of oxide or dust on the switch contacts would give misleading indications. In other words, the drop in resistance which is depended upon to detect submarines is so slight that the apparatus is far too sensitive for practical use. It is strictly in the laboratory class, if at :.*» feasible. Even if We were to admit its practicability, it is obvious that this suggestion is intended primarily for harbor defense works and is hardly applicable to hunting the U-boat on the high seas.
Probably borrowing a leaf from the method employed in France for discovering unexploded shells on erstwhile battlefields about to be plowed, the Hughes induction balance has been suggested as a means of locating submarines. This delicate electrical instrument, as is well known, detects the presence of metal bodies at a considerable distance—in the laboratory, but in connection with the submarine problem it is doubtful if it could be made sufficiently sensitive to detect Uboats at an appreciable distance. Indeed, the main difficulty with this and many other suggestions is that the U-commander very unobligingly keeps his craft at a distance far beyond that at which it may be detected. Still, the Hughes induction balance principle may not be altogether hopeless if developed on an ambitious scale.
Simple to make, inexpensive and evidently practical, the tell-tale net sugegsted by Mr. Lewis B. Shader, of Union Hill, N J., presents an interesting example of what can be done in the way of mechanical contrivances. He proposes using a net of quarter-inch twine and 20-foot mesh, supported from a bamboo rod float and provided at the bottom with a bamboo stretcher, passes up along the side of the net, through a detachable ring at the end of
the b.imboo float, and then pays out several hundred feet until it reaches a tell-tple buoy. The net is made on the unit principle; that is to say, a number of them may be combined by means of a simple flexible connection. The twine-or rope may be colored green, so as to be indiscernible at even a small distance away, and additional floats may be provided.
According to Mr..Shader these nets can be manufactured in very large quantities, because of their simplicity and low cost, and their weight and bulk is such that they can be carried in large numbers by torpedo-boat destroyers and submarine chasers. The nets can be scattered about promiscuously on the high seas, particularly where submarines are known to be active. The action of the telltale net is this: The submarine, running submerged. runs into the net and becomes ensnarled in it without the commander«, being aware of the fact, for the reason that the. twine is light and produces no sound, and in no way affects the motion of the U-boat. However, as the underwater craft proceeds with the net it trails behind it the surface buoy. whMi effectually tags it, so that nearby surface craft can detect its ptesence and follow it. While this feature alone is sufficient to make the tell-tale net effective, Mr. $hader suggests using a trolley bomb which can be applied to the end of the steel wire or cable. For this purpose the surface craft speeds up to the buoy, which is picked up, and by pulling slightly on the cable causes the connection between it and the bamboo rod float to be broken. Thus the steel wir« goes directly to the bamboo stretcher which, together with the net. is wrapped about the submarine, and ^ when a contact bomb is placed on the wire it should be possible with some manupuvring to slide it down against the side of the U-boat with disastrous effects to the latter.
All in all. this suggestion has much to'commend it. and might well be used as a model by others working on the submarine problem..
If the eyes are of little value under water the same is fortunately not true of the ears; for water is a most excellent conductor of sound and lends itself nicely to sound delecting systems. The fact that there are no socalled zones of silence in the water and thpt it is a homogeneous medium permits of the use of sound-detecting system with every advantage at the outset.
It is understood that much i« being done in the way of employing megaphones for'the detection of submarines, and some of these systems have already reached a remarkable state of development, permitting not only the presence of a U-boat to be detected, but also its exact position so that the range can be given to a gun crew. It is well to add here that the original microphone system employed by the Entente Pqwers some time ago operated -quite satisfactorily, according to reports, until the Germans saw fit to mount their motors on soupd-absorbing bases, thus making their submarines practically silent and foiling the megaphone ears of the British and French land stations. However, the latest system of microphonie detection do not rely upon the submarine’s hum, hence it is of no consequence whether the Gerntalh craft ate noiseless or noisy, running at top speed or resting on the bottom. .
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