(Rivista Marittima, February, 1954)
Until a few years ago the day attack by torpedo-boats was considered a possibility against crippled ships only, as in the case of the Souvarroff at Tshushima. Its employment against uninjured vessels was considered justifiable in certain cases on account of the advantage which might be gained through the confusion caused in "the enemy's formation, even though there were no other result.
To-day, the longer range of the torpedo and the increased size of the battleship—with the consequent importance to be attached to the destruction of a unit representing such a concentration of power—lead us to believe that the possibility of the day attack is increasing, and to formulate our ideas upon the methods by which the attack is to be delivered.
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If two torpedoes are fired at the same target, we may apply the the term "difference in paths" to the difference between their respective distances from the center of the target as they cross its course.1
It is evident that, if several torpedoes are fired "in multiple," or "in salvo," from a torpedo-boat, at the same target, the difference in paths between two adjacent torpedoes should be a little less than L, where L is the length of the target.
1The author evidently refers to algebraic difference.
In fact, the requirement that there should be a sufficient dispersion of the torpedoes, that is to say, an appreciable divergence of their paths, follows from the fundamental axiom which, in a former article, we stated in the following terms: "Dispersion of the shots of a salvo is a desirable thing in gun-fire, but it is not to be sought after in the case of torpedoes. A similar case in gun-fire would be one where the conditions would be such that we could not improve the firing owing to inability to observe the points of fall of the shot, and each shot being capable of destroying the target."
It may be asked whether it would be disadvantageous if the difference in paths of two adjacent torpedoes were greater than L. The answer is in the affirmative. In fact, it is sufficient to bear in mind the width of the zone which includes 50 per cent of shots, which, in the above-mentioned article, we calculated for a 9000 meter, 25-knot torpedo, assuming mean errors of ± 2 knots in estimated speed and of ± 10° in estimated course of the enemy, and assigning a speed of 18 knots to the target. With these data—which are most favorable to the torpedo—and with the angle of impact corresponding to the minimum width of the above-mentioned zone, we find the latter to be about 500 meters for a run of 5000 meters. And since, according to the theory of probabilities, the necessary width of the zone which will contain all shots is four times the width of the zone which will contain 50 per cent of them, it follows that in firing torpedoes with mean errors within the limits mentioned, it is not improbable that the deviation of the torpedo from the center of the target will be rather considerable. From this we conclude that, in firing torpedoes, the center of impact may be decidedly to one side of the center of the target, and that, therefore, torpedoes should be fired so that they shall form an impassable chain; in other words, the difference in paths between two adjacent torpedoes should be not greater than L.
A fortiori, it is not logical to allow a dispersion greater than L between two adjacent torpedoes on the ground that the target consists of several ships in formation; since, with the number of torpedoes carried by a torpedo-boat, the attempt to hit several targets means to hit none at all.
Let us assume, then, that a torpedo-boat fires in such a way that the difference in paths between two adjacent torpedoes is a little less than L. Under such conditions, it may be observed that, with ships about 200 meters long, cruising in column at 400 or 500 meters, the formation may be considered a continuous target for a salvo of three or more torpedoes. In fact, it is evidently not possible that all the torpedoes of a salvo fired in this manner should pass between the ships of the formation; it therefore follows that unless all the torpedoes pass outside the limits of the formation, there will be at least one ship hit.
A modern destroyer with more than two tubes on a broadside has, therefore, a sufficient number of tubes to fire a salvo such that two or more ships in column may be considered as a continuous target.
Now, from a study of the battleship tactics of the different navies, the strength of the division appears to be fixed at four ships, and it may be assumed that at least the ships of each division will be in column. We may therefore base our argument upon the assumption of a target equal in length to a column of four ships. In the case of a single torpedo-boat, therefore, it is evident that the torpedoes should be fired so that the central trajectory shall, theoretically, pass squarely through the center of a division.
With this in mind let us attempt to establish rules for the employment of a large body of torpedo craft.
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The only rational method of delivering the day torpedo-boat attack is by sending in a large number of boats simultaneously against the same fraction of the enemy's fleet.
The following remarks will help to illustrate this statement:
Naturally, a condition necessary to success is that the torpedo-boats shall remain exposed to the enemy's fire for the shortest possible time; with the large number of guns of medium caliber carried by the modern battleship every instant is precious, and any slight delay in arriving in firing position means a needless sacrifice of torpedo craft.
There are characteristic differences between the attack by night and the attack by day: in the former, the assailant counts upon the element of surprise and upon the difficult conditions under which the enemy must fire; the attack can and should be delivered at close range, in order to compensate for the slight chance of making a hit. On the other hand, in the day attack, delay means failure for the attack, which not only is conditional upon the position of the assailant in the bow sectors of the target ship, but which also must be delivered with the tubes in extreme forward train, when it is barely possible to fire.
In the day attack, therefore, the torpedoes must be fired at long range, without giving too much thought to the angle of impact, or, more exactly, it is necessary to give up the idea—really superfluous at the present day—of having this angle in the neighborhood of 90° in view of the fact that, however great the speed of the enemy, the change in his bearing from the torpedo-boat is comparatively slow at long range.
Granting this, however, it must be borne in mind that, under similar conditions of the angle of impact (that is to say, with angles of 30° to 60° from the course of the target) one torpedo, considered by itself, has only the very slightest chance of hitting; hence, we must remedy this by firing many torpedoes with suitable dispersion.
With a considerable number of boats available it would not be logical to deliver successive attacks, since the various subdivisions would be destroyed piecemeal; such attacks would not accomplish the result of confusing the enemy's line of battle, that is to say, they would not induce his ships to maneuver in a manner not called for by their tactical situation relative to those of his adversary, and there would be even less reason for hoping to hit any ship with a torpedo. It might be objected that a mass of torpedo craft would offer too large a target: for the present, let us confine ourselves to a recognition of the logic of the mass attack, leaving until later the investigation of the proper form of attack in order that the mass of boats shall not offer too deep nor too wide a target.
If the number of boats permits, it is proper to distribute them in widely separated groups in order that at least one group may be in a position favorable for attack. This, however, is subject to the condition that the existence of every group shall be in accordance with the principles we have laid down; it would not be logical, merely because these groups exist, to scatter the attack of a large body, of boats over different divisions of the enemy's battleships.
In other words, the principle of concentration holds in the case of torpedo-boat attack to the same extent that it does in the artillery combat, although the manner of applying it be different. We must not risk the attainment of one object by trying for too many at once; and in order to obtain indirect advantage from the action of the torpedo vessels, that is to say, from the relative maneuvers of the lines of battle, the threat must be real and not weakly expressed.
In the mass attack we might be led to forget the fundamental axiom that there must be suitable dispersion between adjacent torpedoes; in fact, it might be thought that the greater number of torpedoes would allow a concentration of those from each boat or of those from each primary subdivision of the flotilla. In so doing, however, we should be losing sight of the fact that we have recourse to the mass of torpedo vessels in order to compensate for the slight chance of hitting with a single boat; we increase the number of boats in order to be able to fire at a longer range and attack under conditions where there would be only the very slightest chance of success for a single boat or primary subdivision. The fundamental axiom, therefore, retains all its importance, although, by virtue of the large number of torpedoes, we may accept a decrease in the difference between the paths of two adjacent torpedoes, but only because it allows us to obtain great simplicity in our rules for firing, since it is evident that this simplicity is a factor essential to success.
The ideal arrangement, therefore, would be to have all the torpedoes of the flotilla centered, that is to say, they should be so aimed that the mean trajectory will pass directly through the center of the target division, and that the difference between the paths of two adjacent torpedoes, even though fired from different boats, will be a little less than the length of any hostile ship. In practice, we must establish such rules for firing as will allow of as near an approach as possible to this ideal condition.
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Let us remember that, in firing torpedoes from a single boat, there are two methods by which the desired dispersion may be obtained:
1. Simultaneous firing, or the salvo method proper.
2. Firing in succession, with extremely short intervals.
The first method is possible provided the tubes are capable of continuous train with the same ease as a gun. In this case, with the setting of the central tube established, the angles for the others are easily determined from a table in functions of the range and the desired divergence between the paths of two adjacent torpedoes.
Given the difference in the settings of the tubes, and having them all pointed at the target, we shall obtain the desired divergence among the paths of the torpedoes.
With the second method, successive firing, the tubes are fixed in position, parallel to one another, in a pre-established angle of train. In the case of only two tubes they may be given the same angle of aim, arranging that one shall fire when it bears on the bow of the target, and the other when it bears on the stern. With more than two tubes it becomes necessary to assign different angles of aim, as in the preceding method, each tube firing as it bears on the target.
The first method is evidently especially desirable for the day attack, since, as we have already said, even seconds of time are precious; the other system is, however, imperative when the tubes are not capable of continuous train.
There is no need of dwelling upon the details of these methods; we have recorded them merely in order to show that each vessel will fire in the manner allowed by her construction, and that, as we have already stated, the effort must be made toward having all the units of the flotilla fire almost simultaneously; in other words, the whole flotilla must fire in about the space of time required by a single boat.
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We shall call the angle of aim of a torpedo vessel that adopted for her central tube.
Evidently, the desired dispersion among the torpedoes may be obtained through the spacing of the boats, the adoption of suitably chosen angles of aim, and a diversity in the points of aim in the adversary's formation.
In order to choose the method which will be best in practice, let us observe that the elementary subdivision of a flotilla may be regarded as that in which the number of vessels permits of the approach being made in column without offering too deep a target to the enemy's fire. It seems that this elementary subdivision should be the division of three boats, distance being established at 100 or 150 meters. This distance could not be increased without entailing serious difficulties. It is self-evident that division leaders must be separated by the interval of deployment; it is, however, clear that, in order that the various divisions may arrive simultaneously in position for attack, division leaders must be deployed on a line approximately at right angles to the bearing of the center of the target division from the center of the formation of the torpedo vessels, and, therefore, increasing the distance between vessels of the same division will result in the entire mass of boats offering too deep and too extended a target.
The length of a division of torpedo vessels would thus be about equal to the distance between two battleships; and this, as we shall shortly demonstrate, is an arrangement suitable for the attack.
The adoption of different angles of aim among the torpedo vessels may seem correct from the theoretical point of view; however, it seems best to give up this idea in view of the complications we shall encounter. It is certainly better, for the sake of simplicity, to adopt a single angle of aim, to be signalled by the division commander when advancing to the attack, and which is the one corresponding to the mean conditions assumed. For example, we may assume that the angle of aim adopted is that corresponding to the estimated speed of the enemy and to a position of the torpedo vessels 45° on his bow.
In aiming, it will be remembered that the points of aim offered by the enemy's formation are the center and the ends of each of the ships attacked.
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Before explaining how it seems to us that the approach and attack by a flotilla could be accomplished, we give the following as the method by which the firing of torpedoes may be executed by a division.
The division, assumed to bear about 45° on the bow of the enemy, steers as though to meet him; the boats follow their respective division commanders by successive movements. Tubes are held in readiness in extreme forward train, on the side which is away from the enemy during the approach. At the moment the division commander deems proper he changes course so as to unmask his tubes and fires his torpedoes. Each of the following boats, without waiting to get into the water of the next ahead, likewise changes course at an opportune moment afterwards, brings the tubes to bear, and fires at the point of aim which has been assigned to it in the manner we shall now indicate.
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We believe that the employment of a force of four divisions of torpedo vessels for the attack upon a division of four ships may be considered typical.
With this granted, let us suppose that such a force of boats has been kept out of range of gun-fire and has reached a position relative to the enemy such that there is reason to expect a successful attack.
The flotilla approaches in a single column, following the flotilla commander, in such manner that the entire force is deployed perpendicularly to the bearing of the center of the division to be attacked from the center of its own formation. The deployment being completed, the division commanders, followed in succession by the units of their respective divisions, make a simultaneous change of course and head for the corresponding ship of the enemy, steering so as to keep headed for it, and following approximately the shortest route of approach, being careful under no circumstances to get inside the interval established between each other. In other words, the commander of the first division steers so as to keep headed for the leading ship, the commander of the second division, for the second ship, etc.
The result of following such a rule will be that the line of bearing of the division commanders will remain nearly perpendicular to the bearing of the center of the target division from the center of the force of torpedo vessels, so that the divisions will reach simultaneously the firing position. At the proper moment division commanders change course simultaneously and bring their tubes to bear, followed by the boats of their commands in the manner described above. Vessels of each division fire respectively at the bow, center, and stern of the enemy's ship assigned to their division.
This is a system which seems to approximate closely enough to the theoretical requirements in the simplest manner allowed by the necessities of practice. A similar attack possible of trial even at a range of 7000 or 8000 meters, with sufficient chance of success, or with a chance of success at least proportional to the risks run.
It will be objected that the enemy will not fail to deliver a counter-attack with his destroyers. It is to be observed that, in this way, he will blanket the fire of the battleships; in any case, torpedo defence is not the subject which we proposed to deal with in this article, which is confined simply to setting forth an idea as to how the day attack by torpedo craft might be delivered.