SUBMARINES have been a part of our Navy for something like twenty years but only recently has any attempt been made to incorporate them as a part of the fleet. During the early stages of submarine development, when the Porpoise and the Shark were the “queens of the seas,” the time of the officers commanding them was spent in trying to make them run at all, and beyond an occasional attempt to torpedo a target (probably stationary) no tactical data was ever obtained and probably little thought was given the subject. It was really not until after the World War that much thought was given to their capabilities as, prior to then, no one ever heard of much else than their limitations. During the war, submarines made a name for themselves, not enviable, but well known and thoroughly feared. The fear that they brought to the hearts of surface craft officers and crews may have left an impression that is not quite correct as to their capabilities. It is for the above reasons that the following outline of the capabilities and limitations of submarines is submitted. It may not be entirely correct, but if it causes the service at large to think about submarines in any other than a horrified or disgusted manner it will have accomplished its purpose.
In the first place the modern submarine is a surface ship with the ability to submerge completely, remain in that condition long enough to do certain definite things, and then return to the surface, ready to repeat the performance only after certain definite conditions are fulfilled. To give a surface ship the ability to submerge and return to the surface it was necessary to make radical changes in the design. These have taken the form of the installation of large and cumbrous storage batteries to supply power when submerged; a change in hull shape and strength to withstand the high water pressures at great depths; the installation in the hull of large tanks which may be filled with water to destroy the surface buoyancy; the fitting of planes for control of depth while submerged; the addition of long periscopes which give a certain degree of vision to the officer on watch and the development of a special engine with which to propel the boat on the surface and to renew the electric power in the storage battery after emerging. All these things have contributed to make a new type of ship which the service at large understands but vaguely. I will try to list the various capabilities and the corresponding limitations so that this valuable arm of the fleet may be better understood.
To start with: A long cruise—say 10,000 miles—is quite practicable. Provisions and fuel can be carried for a trip of that length. No one of the crew of a submarine would care to start on so long an uninterrupted run, as the living conditions are not what they should be and at the end of it all hands would need a week in which to rest before doing anything else. Such a trip would require about forty days at a minimum and would leave the crew pretty well done up. If this long trip were reduced to 4,000 miles a certain reserve of strength of personnel would be left that would admit of more or less protracted war operations at the end of the cruise. The two features are complementary and the extension of one automatically reduces the other. The additions and change of design of the surface type to permit submergence have left the submarine crowded, shorthanded, with consequent hard watches, poorly ventilated and tremendously active in a seaway. There is no room for setting up exercises except in a dead flat sea which is seldom encountered on a long cruise. These conditions result in loss of tone by all hands and at the end of a ten-day trip a run on the beach is almost imperative. The same conditions that make the submarine poor living quarters also make poor working quarters, in that the machinery is so closely crowded that repairs on one piece usually require the disassembling of others. Under these conditions the repair work at the end of a cruise is apt to look appalling when first listed. The combination of run-down physical and mechanical conditions after a long run makes it imperative that a period of rest be given before extended operations against the enemy be undertaken.
With the submarines at present with the fleet, a thirty-day cruise would require about ten days’ recuperation and overhaul; a cruise of two weeks would probably require about five days or even less. This does not mean that the boats would be entirely unfit for war operations on reaching their destination, for there is no doubt that the American bluejacket can put across the last drop in him, even after it is apparently gone. A few days of rest and exercise after any extended cruise will, however, materially increase the efficiency of the following war operations. All officers who have served on small ships will appreciate this condition.
Next we will think of the submerged work. As everyone knows, it is necessary to destroy the buoyancy of a vessel to sink or submerge it. As indicated above, this is done in a submarine by the admission of sea water to the ballast tanks. By the use of small tanks the amount of water in the boat is varied so that if a good “trim” is obtained the vessel has practically neutral buoyancy and is about equally heavy fore and aft. If the trim is perfect the boat will “balance” with only a foot or so of periscope above the water. If it is not perfect she will either sink or rise. Owing to the varying density of sea water, wave action, and movement of personnel within the boat a trim is never perfect and it is necessary to use the forward and after planes and the power of the propellers to maintain or change depth. The screws supply all power for advance through the water and for change of plane or depth in the water. The planes are merely large fins extending out from the side of the hull and capable of rotation around a horizontal axis. If they are inclined down she will, of course, sink, the change of depth resulting from the force of the water impinging on the inclined plane surfaces. The rate at which change of depth is made depends entirely on the rate of travel through the water and is a function of the speed and the angle of plane to the horizontal and is, therefore, to a great extent under the control of the diving officer, although his control is affected by his proximity to the target (allowable variation of speed), the state of the sea and the expertness of his crew.
With the above points in mind let us consider the attack of a submarine on a screened battleship. If he is alone, that is, there are no other submarines attacking in the immediate vicinity, and he has been able to pick up his target from well ahead, the problem of the commanding officer is quite simple. He submerges before being seen and closes his target at maximum speed until he can definitely decide on his course and speed, ascertain the nature of her screening forces and their relation to his target—in other words make a logical estimate of the situation.
During his first approach at high speed he has been running at about seventy-five feet, deep enough to be clear of casual traffic and possibly avoid an outer screen. When he decides it is time to take a look and make his estimate of the situation he stops and listens to ascertain the proximity of the screen or other craft. If he decides that all is clear he comes to periscope depth and examines the situation closely at a dead slow speed in order not to leave a wake by which he could be recognized and attacked before delivering his own attack. After reaching his final decision he goes to his attacking course, starts his watch and other tracking instruments and proceeds at the speed necessary to “get in.” The anti-submarine screen is his chief worry now. This he will evade if his listeners are well trained and his own experience and judgment are sufficiently good. His next “look” will come only when his listeners report that the screen is astern and his watch tells him that it is time. This exposure of his periscope will probably be his last before firing, after which he will try to make good his escape.
The above outline of an attack sounds much easier than it really is for there will be many unforeseen situations and his crew will never be trained to the point that everything will work out as planned. It is given, however, to give the service a picture of what we try to do. It has been done and, as we get more experience with the fleet, will be done more often and with a greater chance of success. This can be done, not only by one boat working alone, but is quite feasible of accomplishment by a section of three or four boats working as a unit. It requires more training, greater permanence in station, and all the other factors that tend toward successful cooperation, but it can be done if conditions of sea and light are favorable and the training of officers and crews is properly carried out.
The conditions outlined above are those which might well obtain in war under favorable circumstances. Now consider the chances of success under very adverse conditions. Take a number of submarines, all of which sight a force of capital ships at about the same time. Their missions are all the same and they have been placed on the circle of visibility to report the exit of this force from a harbor and to attack if possible. The capital ships are expecting a submarine attack and are well screened close up with swiftly moving zigzagging destroyers, besides having an outer screen, covering the exit, of several squadrons of destroyers moving at such a rate that the time interval between them is from thirty to forty-five seconds, as it would be if they used a speed of 20 knots. All these destroyers are armed with depth bombs which, if they really believed submarines to be in their area, they would drop at frequent intervals. Under these conditions the capital ships need not fear a submarine attack. If the light screening forces are numerous enough to maintain the screen outlined they never need fear such an attack. It will not be made for the reasons indicated below.
In the first place, there would be the danger of collision between attacking submarines. All of them would be bound for the same point and as their primary mission was information they would not be in a position to concentrate for a united attack. When several ships are all headed for the same place it is very probable that two or more will get there at the same time, particularly when they can’t see. A collision submerged need not be fatal but it is something to be earnestly avoided.
You ask “Why can’t they see?” You will remember that it is necessary to use a very slow speed on exposing the periscope when in the vicinity of other ships to avoid detection. This slow speed makes depth keeping difficult. Listeners will be helpless, for with eight or nine ships moving rapidly overhead it will be impossible to distinguish one from another. If one of the submarines decides to chance it and gets into the mêlée, his first sight on exposing a periscope will probably be that of a destroyer charging at him at a rate of 20 to 30 knots. When it is realized that the maximum field of a periscope is only 34° and that a destroyer may be charging him from any one of the 360° it makes his position that much more perilous. Still, consider the submarine in the mêlée and that the periscope has shown a destroyer crossing his bow so that danger of collision is imminent. What can be done? He will try to dive under as that is the only hope of escape. He is going at from 1 to 20 knots. His rate of change of depth in smooth water will be not greater than one foot in twenty seconds at first and maybe after he has started down will increase to a foot in fifteen to twelve seconds. As he must drop at least ten feet it will take him approximately three minutes. In this time a destroyer at twenty knots can go one mile. His chances are slim. His time of diving will be decreased if he can speed up but remember he has a ship weighing a thousand tons to accelerate from one knot to something like five before any material increase in diving speed is actually gained. His turning circle is many times that of a destroyer, and the Y-gun has made a destroyer very broad in effective beam. As was stated before, the battleships are effectively screened, and it is doubted that any submarine could get through such a screen and make an effective attack. If it did it would be marvelous good fortune and make the commanding officer eligible for all the honors that the Allies and the Central Powers combined could shower upon him. What these boats would actually do under the above conditions would be to gain as much distance as possible in the direction of advance of the enemy and lay in wait for him in hopes that the screen would thin out and night time or twilight would give submarines a favorable opportunity for attack.
The above discussion will indicate that there are times and places when a submarine attack on screened forces is practicable and, contrariwise, there are conditions that forbid such an attack.
The strength of a submarine lies in the fact that she can see without being seen. This is her one claim to fame. Before the war developed the depth bomb and the listening devices she could escape counter-attack by submerging, leaving the enemy without a point of attack. But the old race between armor and projectile took a side shoot during the World War with the result that the submarine has lost much of its protection heretofore gained by submergence and must now take its chances with counter-attack which only luck, aided, of course, by skill and knowledge, can forfend. Surprise is the one great advantage.
This feature is most easily gained bv a submarine on patrol. She is sent to an area known to be frequented by the enemy. At daylight, or just before, she sinks quietly to where only a foot or so of periscope is above the water. With two feet of periscope out she has a horizon of nearly two miles. The tall masts of a ship add several more to this. It is an easy matter to lie in wait and deliver a torpedo attack on a passing troopship or cruiser. Every advantage lies with the submarine. This method of patrol can be made into a blockade of an enemy port or into an outpost for information. If it is the latter she can forward the news collected or deduced to her superior at night when she comes to the surface to recharge her storage batteries.
On this patrol her listening devices will give certain information before her periscope can gather the details. During the last war, American submarines formed an anti-submarine patrol in shipping lanes off the coasts of England and Ireland. The listeners, each on duty twelve hours a day either at the S.C. tube or radio, soon became expert and could always tell whether the propellers heard were those of a destroyer, submarine or trawler long before the periscope gave the information. These details were of great value but they were not enough. Before an attack could be made or an escape executed it was necessary to see what the ship was doing.
The other day an old shipmate asked if it wouldn’t be possible to lie on the bottom in a submarine, his idea being to get all information necessary from the listening devices and to conserve the storage batteries. Of course it is possible to lie on the bottom in a submarine. All that it is necessary to do is to run down and then take in enough water to give the boat negative buoyancy sufficient to keep her from pounding due to the wave action. This amount of “negative” will vary with the depth of water and the condition of the sea on the surface. The higher the sea in relation to the depth the greater the amount of “negative” required.
But, after getting on the bottom what good is the boat? There can be no question of surprise and no real probability of an attack—certainly not while on the bottom. Consider a boat lying on the bottom at a depth of 150 feet off the entrance to New York in November (I mention the month to give an idea of the surface conditions). To keep from pounding due to wave action from two to five tons of negative buoyancy will be required. A great deal of shipping will pass overhead during one daylight period. Well trained listeners will be able to report with considerable accuracy whether the engines driving the screws that are heard are reciprocating steam engines, turbines, or internal combustion type. By plotting the bearings of these sounds we can get the approximate course and speed of the ship. But what have we gained by this? Nothing.
If our mission is to obtain information to be reported later, we might be able to report “a flock of turbine-driven vessels, probably destroyers, headed east, passed out at noon.” That information might be of value but it couldn’t be reported until night when it might be too late, and if a periscope patrol had been used our information would have been increased by giving the exact number and types and whether or not the ships had changed course to the southward after passing our audible horizon. Also, with a periscope patrol it would be possible to run off the beaten track and, if the information were important enough to warrant giving away our presence, come to the surface and broadcast it immediately.
If the mission be attack then a patrol on the bottom is worse than useless. Suppose our “flock of turbine-driven vessels” really consisted of a division of battleships screened by destroyers. Before any attempt at attack could be made it would be necessary to rid the boat of the negative buoyancy taken on to prevent pounding. This would have to be done by pumping, for if the water were blown out the measurement would be inaccurate and too much might be blown, making the boat too light and incapable of control at slow speeds. By the time the boat could leave the bottom and reach periscope depth our target would be a mile ahead and making such speed that attack would be impossible. It is believed that the above remarks show the futility of such a patrol when compared to that at periscope depth, in which condition the submarine is ready for any eventuality.
To be able to bottom has, however, advantages under certain conditions. If being trailed with listening devices and depth bombs it might be very convenient to rest on bottom and stop all auxiliaries that might make a betraying sound.
Submarines can be used as scouts under certain conditions when it would be bad policy to use a surface ship. This is particularly true when negative information is valuable. Three or four submarines could thoroughly search an area of considerable extent by cruising on the surface and diving at the approach of a surface ship. In this way a report in considerable detail could be given without the enemy knowing of the reconnaissance. To use submarines in a search requiring immediate report of conditions and possible screening is open to discussion. The limit of horizon from the upper works of a submarine is in the neighborhood of five miles. It is doubtful that numbers and types of ships could be accurately determined at a much greater distance than eight miles. If the submarines are sighted by the enemy and forced under, their usefulness as scouts is greatly reduced, but their function as a distant screen still remains. Scouting and screening ahead is really dependent on the speed of the main body. If that is low enough there is no reason why submarines could not be used as a screen of a slow train or troop transport. From a position well ahead they might easily reduce the attacking force to numbers that the escort could control.
One bad feature of using submarines with a merchant convoy is that to the average merchant master all submarines are dangerous. This was forcibly brought home during the war when O-6 was nearly sunk by the gunfire of her own convoy. The submarine has no friends during hostilities. There is, however, a definite place for submarines in scouting and screening operations.
Operations against enemy communications are feasible if properly carried out. Submarines can and will sink enemy ships carrying stores and munitions. The Germans gave submarines a black eye by doing just this in an unlawful and cruel manner, but the British accomplished it in the Sea of Marmora without raising any cries of horror and other nations will use this type of vessel for the same thing. The United States refused to become a party to a treaty to abolish submarines, because we could see legitimate uses for them in this very line.
If you should read “operations against enemy communications” and think that the cutting of transoceanic cables is meant, please cast it from your mind. The submarine of Jules Verne has not been developed in the United States Navy. We can not go to the bottom and open a door to the sea, allowing our personnel to cut cables or to hunt submarine game with air rifles. One of our early submarines, G-3, was fitted with such a compartment and was fitted with wheels like the famous Nautilus, but this type has long since been abandoned and the space thus used made available for torpedoes.
Mining from submarines was developed by both the Germans and British during the World War. It has the element of surprise attached to it that is so necessary for successful submarine operations. A submarine mine layer can lay mines just after the sweepers have reported “all clear” and no one will be the wiser until he chances to explode one against his bow. Attempts have been made to obtain funds for development of this type, but as yet without success. There is no doubt that these boats will be used in the next war and that success will crown their efforts. In the meantime, our Navy is not learning to build or operate mine-laying submarines and will be that much behind when the time comes.
During the war a good many “stunts” were done with submarines which proved that they have values other than those usually attributed to them. Several British submarines passed under the mine fields of the Dardanelles. After entering the Sea of Marmora and the Bosphorus, these boats were of great value in cutting communications between Asia and Europe, blowing up bridges and sinking transports. A submarine, being able to operate in three planes, can introduce its own element of surprise quite frequently. The Germans landed spies on the coast of Ireland and went in to get information from spies already ashore. The result of this kind of work was apparent and it can be repeated. A submarine reconnaissance of a port or fortification can be and has been made, but the value of the information gained in this way must not be placed too high. It must be remembered that the observer is looking with one eye from a very low position and he gets no perspective. The magnification of a periscope is only six diameters and the details that are missed will materially affect the value of the report. Certain information may be obtained, however, and under certain conditions this might be a valuable method of scouting.
There are many other methods of using submarines, some of which may be revolutionary, and no attempt is made here to list them all. The only excuse for this paper is to try to give the service a general idea of our capabilities and of our corresponding limitations. When submarines have been with the fleet a few years longer and have learned more about themselves, the officers of the fleet will have learned a correspondingly larger amount. Until this happy day arrives, please do not look on us with horror or disgust but try to remember that a submarine is built for certain definite functions and to obtain those had to sacrifice certain features which are desirable and without which our limitations are great. Later development is bound to bring improvement but we now have submarines which have high value in their own sphere and as we progress in their use this sphere will widen considerably.