The Relative Importance of Turret and Telescope Sight.
By Rear-Admiral Bradley A. Fiske, U. S. Navy.
The value of the turret is recognized. The victory of the Monitor over the Merrimac was so opportune and dramatic, and its results were so evident, important and immediate, that the turret was at once proclaimed, by all the world, to be one of the greatest inventions of the age.
The telescope sight, on the other hand, made its obscure little debut on a small gun-boat, way up in Bering Sea; its value was not realized for ten years; and it grew so slowly into use that it came gradually to be regarded as a " matter of course." Though adopted now by every civilized navy in the world, it has nevertheless received no individual recognition; and yet there are some who think that it is a more important factor in naval warfare than the turret.
To compare the relative values of the turret and the telescope sight, let us imagine two ships, A and B, meeting on the ocean and fighting; A having open sights and turrets, and B having telescope sights and no turrets, B's guns being arranged in broadside.
Which ship would whip?
A would be able to fire, say, ten guns on a broadside, and B only five. As to firing ahead or astern, B's guns would probably be disposed according to the old-time plan, with the forward and the after guns on two different decks, so that she would be able to fire four guns ahead and four astern, the same as A.
Of course, the proper tactical utilization of greater accuracy of gun fire would dictate that B should keep at a very long range and not present a long target laterally, so that B should keep A on his bow or quarter as far as practicable. But in order to make our comparison applicable to a fleet action, we have to assume that both ships turn their broadsides to each other, and engage at some moderate distance, say 10,000 yards. In this case, A could fire twice as many guns per minute as B; so that, if the accuracy were the same in the two ships, A would probably hit B twice as often as B would hit A.
But the accuracy would not be the same. It is impossible to state exactly what the ratio of accuracy would be; but it certainly would not be unfair to the open sight, if we accepted the same ratio as characterized the performance of the two sights on the only occasion when their value could be compared under identical conditions. This was the first time the telescope sight was ever tried. It was on board the Yorktown at Unalaska, on September 12, 1892. A diagram of the firing is here shown.
If anyone will take the trouble to measure off the vertical deviations of the two series of shots, he will find that the mean vertical deviation of the shots fired with the open sight was 6-54 feet, and with the telescope sight 2.25 feet, the ratio being as 2.91 to 1. This is on the supposition that the five shots fired with the open sight, and which could not be plotted on the diagram (which extends 15.75 feet above the mean point of impact), had a mean vertical deviation of 15.75 feet. If he will also measure the mean lateral deviations of both series of shots, he will find that they are 8.90 feet and 2.75 feet respectively, the ratio being as 3.23 to 1.
It is not here claimed that the shots were plotted with mathematical accuracy, but that they were plotted with a sufficient approximation to accuracy to form a fair basis of comparison, and as accurately as the appliances of that day permitted. The fact that the fourth shot brought down the target in a mass on the raft, and that the target was found to have three holes in it when examined, indicates that the shots fired with the telescope sight are quite accurately plotted.
The fact that the last shot, fired with the telescope sight (No. 23), was fired at the vague mass of wreckage, and therefore ought not to be counted, is here ignored.
Certainly it could not be objected with reason that the ratio, 2.91 to 1, is unjust to the open sight. The great accuracy of naval gunnery to-day, as compared with its accuracy before the invention of the naval telescope sight, indicates a much larger ratio than 2.01 to 1; and this larger ratio cannot be due to improved methods of drill and training, or to the effect of spotting and fire control; because, while these things increase the rapidity and the effectiveness of the fire of a group of gnus, they do not and cannot increase the accuracy of the fire of any individual gun beyond its own inherent accuracy. They simply utilize that accuracy.
Suppose A and B approach to a distance of 10,000 yards and begin to fire. It is clear that the vertical target presented by each ship would be about 30 feet, and the mean vertical deviations of A and B about 49.5 and 17.03 feet respectively; so that, referring to page 129 of Alger's Exterior Ballistics, we see that the respective probabilities of hitting, in the case of each gun in the respective ships, would be in the ratio of about 2.71 to 1 in favor of B, supposing both ships to have their mean points of impact on the centers of their respective targets, a supposition not unjust to the open sight.
The vertical deviations, 49.5 and 17.03 feet mentioned above, are based on the assumption that if the deviations with the open sight and the telescope sight were 6.54 feet and 2.25 feet respectively at 1320 yards, both deviations would be increased in the ratio 10000/1320 at 10,000 yards. But both would really be increased more than this, because not only does the deviation, with a clear target, increase as the range, but the target becomes dimmer, thereby causing increase of deviation; and this increase of deviation would be greater with the open sight than with the telescope sight, for the reason that the telescope clears up the target and gives a definite point of aim.
The figures 49.5 and 17.03, therefore, are not unfair to the open sight, but the reverse.
By reason of the great lateral targets presented by the ships relatively to the mean lateral deviations of the guns, the superior lateral accuracy due to the telescope sight would have little weight, and it is therefore ignored here.
It is impossible to reason out which ship would begin to fire first. So it must be assumed that they would begin at the same time.
B, of course, would use salvo firing. Whether A would or would not use salvo firing, it is impossible to say; but it is safe to say that he would do better by not attempting it. Previous to the introduction of the naval telescope sight, salvo firing with open gun sights had been found extremely inaccurate and was only used at very short ranges. Some ships, especially in the British Navy, were fitted for salvo firing, but by electricity and from a "directing station," where the officer who fired the battery, used a telescope for sighting.
It seems sure that A's fire per gun would not be so rapid as B's. B could fire her five broadside guns in salvo once in 30 seconds. But with the open sight, where the main difficulty was in getting the pupil of the eye exactly on the line joining front and rear sights at the same time the line of sight was on the target, a "gun-captain" had frequently to wait a long- time after his gun was loaded before he could get " a good sight." It must be remembered that it was necessary for him to have his pupil on the line of sight not only in the vertical plane, but also in the horizontal plane; and that if he lost his chance at the end of one roll he would have to wait until another roll came along. Besides this, A's firing would undoubtedly be handicapped by the smoke of one gun interfering with another gun, and, in the case of any single turret, by the fact that one gun would have to wait until the jar caused by the other gun had subsided.
Bearing in mind the fact that the firing on board the Yorktown was done at anchor in smooth water and at an anchored target, when it was comparatively easy to keep the pupil of the eye on the line of sight, so that the conditions were much more favorable to the open sight, as compared with the telescope sight, than would obtain under ordinary conditions on board a ship under way at sea, firing at a moving target, it would seem that, in order to attain the relative accuracy of fire between A and B, which was found on board the Yorktown, the rate of fire per gun of A would have to be extremely deliberate; certainly not greater than one shot per gun per minute, about one half of that of B's guns. That is, the number of guns fired per minute on board the two ships would be about the same.
This means that the hits per gun per minute would be as 2.71 to 1, in favor of B, supposing that both ships got their mean points of impact on their respective targets at the same instant, and supposing also that there is no cumulative effect in an "initial advantage."
But they would not get on their targets at the same instant and there is a cumulative effect in the "initial advantage."
B's spotter, after one or two ranging shots, would probably straddle the target with his first or second salvo, and in about a minute after the first ranging shot would begin to land 25% of hits on A; that it, 2 ½-12 inch shots per minute.
It is highly improbable that A could get his mean point on B by this time. His task would be extremely difficult. Not only would he have a large dispersion in range to deal with, but, as the projectiles would not fall into the water together but separately, and at irregular intervals of time, his calculations as to how much to raise or lower would be complicated by the necessity of remembering how the various shots fired with a certain sight bar range had fallen; and it would be practically impossible to even ascertain this after he had raised or lowered once, because he would not know whether the last shots had been fired with the last range he sent down, or the previous one. His difficulties would be increased too—compared with those of B's spotter—by the larger lateral dispersion.
All these difficulties would increase after B began to hit; and then the people in the turrets, conning tower and elsewhere would begin to have their troubles. These troubles would increase, and would cause confusion, and would progressively augment B's initial advantage; so that it is possible that A might be defeated without ever getting his mean point of impact on B at all.
But let it be imagined that both ships get on their targets at the same instant, and that B's only advantage is the relative probability in h. p. g. p. m. of 2.71 to 1 in B's favor.
The only advantage which A would have to oppose to this offensive advantage would be the defensive advantage due to the superior protection given by her turrets: and this would simply be due to the fact that the ports through which B's gun would have to fire, in order that the guns might have a sufficient train, would be much wider than the ports in A's turrets. But the width of B's ports perpendicular to the line of fire would not be greater than the inside diameter of A's turrets; that is, about three times the width of A's ports; and the lateral target of even a whole turret is so small, relatively to the mean lateral deviation of the gun, that the superior probability of hitting laterally attained with the telescope sight (ratio about 3.11 to 1, assuming the data of trial on board Yorktown) would have to be taken into account; so that the probability of hitting a turret or anything of similar dimensions would be, not as 2.71 to 1, but as 2.71 x 3.11 to 1, equal to 8.43 to 1, in favor of B.
Therefore, the greater width of B's gun ports would be more than counterbalanced by the greater probability that A's ports, or the guns in them, would be hit; and the probability of a shot entering a port or striking a gun would be about as 8.43 to 3 in favor of B.
The probability of striking a gun would, of course, be about 8.43 to 1, in favor of B.
It will be noted that no account is taken here of the fact that the turret itself, or the armor in front of and over the broadside gun, is not really invulnerable; and that, even if it were, the shock of receiving a 12" shell would be very detrimental to the personnel and material behind.
There would still remain, therefore, the original probability of 2.71 to 1 in favor of B, an advantage nearly equal to the advantage that three sister ships would have over one other sister ship.
Of course, the ratio of probabilities would really be much greater than this, but to a degree that eludes computation. This ratio of 2.71 to 1 takes account merely of the probability of hitting the areas exposed by the entire ships as targets. It disregards entirely the advantage B would have in his ability to use salvo firing, the cumulative effect of "the initial advantage," which B would get at the start, and the advantage B would have in being able to direct his fire at will on individual parts, such as the conning tower. It also neglects the fact that the probability of hitting the conning tower would be about as 8.43 to 1 in favor of B.
It would seem then that B would whip A, and quickly.
We have thus far limited our comparison to gunnery warfare. But there is another very important field of naval warfare, and that is torpedo warfare.
So let us suppose that A and B are attacked by destroyers, in the daytime. At night, the telescope sight has an unquestionable advantage, but it is small.
As the destroyers would head towards their respective target ships, the lateral targets presented to those ships would be so small that the smaller lateral deviation due to the telescope sight would have to be taken into account, as well as the smaller vertical deviation; so that the probability of hitting the area presented by a destroyer would be about 8.43 times as great with the telescope sight as with the open sight.
This means that, with a given degree of risk, one group of destroyers would have to keep nearly three times as far from B as the other destroyers from A; and that B's chances would be 8.43 times as good as A's.
It also means that, if we did not have the telescope sight, destroyers, without taking a greater risk than at present, could approach battleships by day to nearly one-third of the distance which they must now observe; that is, close to the distance at which their torpedoes are effective. In this case, it might be a serious question whether it were worth while to build battleships at all. Certainly it would be a serious question with the Congressmen who appropriate the money.
The destroyer has been gaining rapidly in seaworthiness and speed, and the torpedo itself in accuracy and range. The destroyer has been menacing and is menacing the very existence of the battleship, not only in war, but also in peace; for the strongest argument against appropriating money for battleships is the torpedo. The only thing that keeps away the destroyer is the gun; and a group of destroyers could approach a battleship, and fire torpedoes at her, with considerable chances of success, at 4,000 yards in the daytime, if they were not fired at by accurately sighted guns.
But it is not necessary to limit our supposed attack to destroyers. Let us suppose that A and B are attacked by fast cruisers, whose machinery and torpedoes would be below the water line, so that their degree of immunity from being sunk would be much greater than that of destroyers. Such cruisers, unless in very large numbers, would have no chance whatever against B; but an attack of say six against A would have a respectable chance of success. How many such vessels would be required to sink A, no man can tell; but it is certain that B could stand off at least 8.43 times as many as A could.
Therefore, it is possible that, were it not for the naval telescope sight, the battleship including the turret might have become obsolete before now. It is certain that battleships would have much less than their present effectiveness to plead as a reason for their existence, that they would fall an easier prey to the torpedo, and that we should have had, and should still have, very much more difficulty in getting money to build them.
The turret has no field of usefulness in torpedo warfare, and is applicable to battleships only. The naval telescope sight has an important field in torpedo warfare, and is applicable to all kinds of vessels. Over the whole world to-day, there is hardly a modern gun on board a modern vessel that is not fitted with telescope sights.
In the war between Japan and Russia, the destruction of the Russian fleet at Tsushima was so complete as to end the war. The main cause of its destruction was that the Russian gunnery was less accurate than the Japanese. The more accurate gunnery of the Japanese secured an initial advantage in the beginning of the battle; and this advantage, according to a natural law, increased in geometrical ratio as the battle went on, and became overwhelming in a few minutes.
It has been stated on excellent authority that the Japanese guns were fitted with telescope sights in good order, while very few of the Russian ships had telescope sights, and that the telescope sights which were fitted were not in good order.
If this be true (and it probably is), the reason for the sudden annihilation of the Russian fleet stands out sharp and clear; and we see that the naval telescope sight, more than any other one thing, was the cause of the turning of the tide of history in the direction in which it did turn.
If this be true (and it probably is), the influence of the telescope sight in the Russo-Japanese war was greater than the influence of the turret in our Civil War.