(Extract from a lecture delivered at the War College, September 13, 1901.)
TACTICAL VALUES.
The chief of these owes its existence to the fact that the approach of a boat under water cannot be stopped by gunfire, and that therefore sure torpedo range can be reached in daylight in spite of gunfire, per se. Since the boat at a working depth of from thirty to forty feet cannot satisfactorily direct her course upon an object constantly changing its position, and since a ship cannot only change her position, but can change it at a speed much greater than that possible for the boat, it is evident that the ship could keep out of torpedo range after sighting the boat or otherwise becoming aware of her being in the vicinity before she got home, just as a fast cruiser can keep out of gun range of a battleship. It is very generally concluded that a battleship has a considerable tactical value when opposed to a fast cruiser because within her more limited area of effective action the former can, owing to her strong defensive power in armor and her strong offensive power in gun fire, compel the latter to move out of that area. Just so, owing to her invulnerable defense of water cover and the strong offensive power of her torpedoes, can the submarine compel the battleship to move out of the very closely limited area of effectual action of the boat.
The differences, then, between the tactical values of battleships versus cruisers, and submarines versus battleships are those of degree rather than those of kind; and therefore if a battleship be very good against a cruiser a submarine must have some tactical value against a battleship.
The chief factors that define the boat's degree of value are small radius of effective operation, slow speed, indirect approach when invulnerable to gun, torpedo and ram attack, and the necessary giving up of complete invulnerability from time to time for the sake of correcting direction of approach.
From the data given in the table * it would seem that while the radius of movement calculated for is about 400 miles—though why this distance should not be quadrupled by utilizing ballast tanks for fuel stowage I cannot conceive—the radius of effective operation, i. e., the distance through which the boat could move in continuous diving, i. e., fighting trim at full speed, is less than thirty miles.
* Omitted.
Reducing this distance by the good margin of 33? per cent and making it twenty miles we arrive at a figure which seems to place the boat in the mobile coast defense,—in the offensive-defensive not in the harbor defense class—and to determine the distance off shore from which she could fight all the way into the beach. She could, of course, exhaust her submerged or fighting endurance in one continuous effort, or could come to the surface at a safe distance from the enemy and renew her submerged-running power, or could guard a position all day by using her under water power economically, according to circumstances. With the radius of effective fighting operation fixed at twenty miles, the effect of slow speed becomes apparent. For example, it is clearly seen that if a 14 K. battleship avoided a single 7 K. submarine twenty miles off shore and ran close in, she could operate there about an hour and a half before the boat could arrive and drive her off.
With a number of boats holding a line against the advance of a number of ships the disadvantage of slow speed is greatly lessened, as will be seen if we suppose that a line of 7 K. boats with six mile intervals opposed the advance of 14 K. ships whose direction of approach can be made out at six miles. If the ships came on in column the boat nearest ahead would close to intercept; and since the greatest distance that a boat would have to move through to do this would be half the interval, equal to half the distance the ship would have to move to reach the point of crossing the line, it is evident that as far as speed alone is concerned one or two of the 7 K. boats could reach the point of interception and make matters very interesting for the leading ships; while the ships that succeeded in passing the line would be in the best possible position for the boats to close on and force a second passing of their line by making the inshore region too dangerous for occupancy.
As before, the ships that got through the line could operate inshore for an hour and a half, if, as supposed, all available submarines were put on the line, and none held inshore, in reserve. If the ships came on in line or group formation the boats would of course have a greater number of chances for successful work.
In regard to the defect of indirect approach, it is to be noted that this only becomes serious in long submerged runs, and that tactically, there is no reason or excuse for such runs in the attack upon ships. Such long underwater runs would only be useful when hauling off after the torpedoes were expended.
In maneuvering for position as just supposed the boat would be steered by continuous direct vision till within 6,000 yards or less, at which distance the chance of striking an indistinct target a few inches high at quickly changing ranges from a ship moving at speed may be considered nil. After that and until the ship were within 2,000 yards the dives would be short and the bearing well kept; for it may be taken for granted that the chance of scoring by the guns of a ship moving at 14 K. is practically nil when the object aimed at is a water tinted cylinder a few inches high that disappears for three or four minutes and appears for not more than ten seconds at a time and at a different place each time. If the ship is heading across the boat line, as supposed, the captain of closing boat will know that she will cross the line in from four to five minutes from the time she is a mile away, that the boat will in that case be within sure torpedo range of a broadside target within that time, and so will not stay down more than three minutes. If the ship holds her course the boat will have a sure shot as she breaks water; if the ship changes her course a few points either way the chance for one or the other of the closing boats is still good; if the ship puts her helm hard over and goes about the chance is not good, though with hard over helm the ship would present a fair target at from 1300 to 1500 yards, which with Obry gear and the torpedo really kept in order, would be worth trying for. In this case the loss of a sure shot is due, not so much to the boat's lack of direct approach as to the superior speed of the ship in running away, and it may be remarked that if the ship runs away, the boat has accomplished something. Only when the boat rises within sure torpedo range-400 to 500 yards—does the ship have a practical chance of sinking her; and not then before her torpedo is away. To sink her a fair hit with at least a 4-inch would be necessary—and the gun practice that could be relied upon to do that in ten or fifteen seconds would have to be rather fine.
I have gone into this matter of method of approach, ad nauseam perhaps, because for some reason that I cannot comprehend, there exists, even today, a widespread idea that since a submarine can dive she must necessarily remain under water and blindly grope about there; and that if she does not do so she must be hampered with much befogging terms as submersible, or immersible or emerger or submerger, terms full of sound and signifying less than nothing at all. One hears even in the year of grace 1901, expressions of pseudo-expert opinion to the effect that submarines can never be useful until some method of seeing under water is arrived at. While underwater vision would greatly add to the tactical value of the submarine, provided she possessed this quality and her surface enemy did not, it is sure that, if she could see under water only at the expense of being seen, her utility would be less than it now is, since she could not conceal herself in short dives and could, much more easily than now, be struck by surface craft as she rose for a shot whether she broke water with her conning tower or used a camera lucida or periscope.
The sumbarine is slow always, and intermittently she is blind; but she has speed enough to be useful when working on interior lines against fast surface craft, she does not altogether lose sense of direction when she becomes blind for the sake of becoming invulnerable and she possesses the enormous tactical advantage of that third dimension movement which is denied to surface craft. She can move out of their field of action without going away—or into it at will.
In one of the late British Service Journals there is a statement to the effect that a destroyer stripped of gun and tubes and equipped with a stern towed spar torpedo on a forty foot boom could destroy a submarine by towing a boom against her when she was ten feet under water. Why a submarine should run at ten instead of thirty or forty feet does not appear; nor does it appear how the destroyer could, when the submarine showed for a few seconds, head, for her and strike her with the span torpedo before she attained a safe depth. While the battleship, protected by the destroyer is the proper quarry of the submarine, there seems to be no law against sinking the destroyer in passing if her presence were inconvenient.
Personally I am strongly of the opinion that the primary tactical use of submarine will consist in keeping hostile ships fifteen or twenty miles away from the defended place, in preventing them from passing through points at bombarding ranges, and upon occasion forcing such an extension of the blockading line as to make intervals wide enough for the safe passage of a contained fleet or of merchant craft—in short in making blockades non effective no matter what the force employed. That submarines could do this duty within the area defined, seems clear because within that area it would not be war or common sense to expose expensive ships with large crews to the attack of submarines with small crews, when the chances of war were so largely in favor of the boats. The tactical disposition for this primary use has been sufficiently indicated. It would be such that while there would be a certain concert of action, each boat would have to maneuver independently under general orders to close and strike when possible.
There exists a considerable weight of authoritative opinion in favor of carrying small hoist-in submarines, aboard battleships and large armored cruisers. Small non autonomous submarines—I mean boats incapable of recharging their storage batteries from motors worked on board—as light as 15 tons weight can be constructed and might have a certain tactical value when a weak fleet had to meet a superior one at sea, since the hoisted-out boats might form a rather comfortable line of defense for the weaker fleet to fight behind, or upon occasion to retreat behind.
But the hoist-out boat does not appeal to me because the weight and space devoted to boat carriage would considerably detract from the fighting qualities of the battleship under the more frequent conditions of battle. While all other classes of fighting craft should sacrifice efficiency in a particular direction in order to become a better auxiliary to the battleship, not one iota of the latter's power should be reduced in order that she might better aid other types. If a defensive line of submarines were considered useful to a fleet under special conditions, it would seem better to tow a string of coast defense boats by a convoyed steamer. Submarines can be sealed up and towed for any length of time and they tow well and easily without steering. The crews could board them on balsas in a seaway and have them ready for work quicker than the smaller boats could be hoisted out, and could in fact board them in a sea in which the hoisting out of the carried boats would be a slow and difficult if not impossible operation. The idea of hoisting out submarines in the face of the enemy seems ridiculous. It would seem to me too, that for the attack of ships, dry docks, etc., inside a defended port, the towed or self navigating coast defense boat would be much more efficient than the small hoist-in boat.
I would ask you to receive these personal reflections with a large amount of salt, for I am fully aware that my predilection for homogeneity in type of all classes of fighting craft may prevent a proper view of the advantages of two or three kinds of submarines for two or three kinds of work.
With submarines in the defense of a contained fleet the temptation to use them by the containers would be great; for although the defensive submarines could drive off the surface craft of the latter, they could not prevent the containing submarines from closing to prevent the egress of the contained fleet. At present no one knows how much service submarines may be capable of in distant operations; while their proved efficiency shows what may reasonably be expected of them in the coast defense.
Mahan tells us that "Effective defense does not consist primarily in the power to protect but in the power to injure." The submarine surely has the power to injure in her torpedoes and she has sufficient mobility and sufficient invulnerability to make that power felt within the narrow limits of her coast defense work. If we admit that within the twenty miles off shore limit she may be effective, it follows that certain strategic movements at present considered correct must be broadly modified.
STRATEGIC CONSIDERATIONS.
From what precedes in the discussion of tactical values, it follows that strategic movements for the purpose of blockade of ports, bombardments of places, or containments of fleets cannot be initiated with confidence of success when there are mechanically effective, well organized and well handled submarines in the defensive and none in the offensive.
Also that submarines would hamper fleets more or less, if they were taken along for deep sea fighting, but as they might be useful as a sort of unattackable and quickly placed mine line to fight behind at sea, their presence or absence would influence strategic conclusions.
In regard to the question of bases for occupation upon a hostile coast, it is apparent that the strategic selection would be modified by the necessity for protection against submarine boat operations—that a base otherwise available would be rendered untenable by the presence of the enemy's coast defense submarines.
For example:—Since deep water channels cannot be held by mines or by gun fire against submarines because mines in any channels practicable for ships can be readily attacked or passed by submarines, movable obstructions or other devices would have to be resorted to to insure a safe defense and this necessity would directly influence strategic selection.
Again, with submarines in the defensive and none in the offensive of a base—which will be the usual condition if submarines cannot be used on extended campaigns—the strategic desirability of multiple exit is lessened, since the containing fleet could be pushed so far off as to make one exit as desirable or more within the limit of effective operation of the boat, i. e., two exits twenty miles apart would be only a very little better than one. Two or more exits so far apart that the distance between them was considerably greater than the radius of effective action of the boats would retain a part of their value assigned them when only surface craft are considered. With submarines in both the offensive and defensive—i. e., under the supposition that submarines can be taken across seas—the multiple exit holds its value in kind, though less in degree, than when estimated for upon a surface craft basis.
But the chief strategic value of the submarine, the value which nearly all naval services but ours recognizes, is the limitation she imposes on coast operations by the enemy in the absence of the home fleet, through her power to meet any class of hostile ship upon the coast by day or night with the chances of success in her favor, and through her power of numbers, due to small cost of construction and maintenance, to cover long stretches of coast.
That country most needs the submarine which has the greatest number of wealth centers that may be operated against in the absence of the cruising fleet and which may be forced to send practically all her fleet abroad.
That country is ours in the opinion of a high English Naval Authority, whom I quote:—
"Let us suppose," he adds, "that in time of war 100 French submarines are let loose in the channel at night. These boats have sufficient speed and radius of action to place themselves in the trade routes before darkness gives place to day, and they will be capable of doing almost incalculable destruction against unsuspecting and defenseless victims. The same possibilities apply to the Mediterranean and to other of our ocean highways within the danger zone of the submarine. The submarine boat has thus increased the value of the mechanical torpedo tenfold. To the United States of America it will be of inestimable benefit, as it will render the coast practically secure against attack from any country excepting those having naval bases within easy striking distance of their littoral."