It took over 300 years to perfect the two inventions which form the essential features of the modern gun,—to develop the two ideas of breech-loading and rifling to the point of practical efficiency. The breech-loading rifled cannon, built up of steel forgings, and firing elongated steel projectiles with a muzzle velocity as high as 2,000 f. s., was the result of this development. In recent years there has been a great increase in the rapidity of fire of guns, due to gradual improvement in the details of breech mechanism, loading appliances and gun carriages, and a great increase in the power of guns, due primarily to the invention of smokeless powder; but the material and system of construction of the guns have remained unchanged. Is there good reason for this, or will the course of further development lead to the adoption of some other system?
Many think that wire winding, first proposed by Dr. Woodbridge, of Washington, is the coming system. Wire-wound guns, however, though known and experimented with for many years, have never come into general use, and, indeed, until one of their strongest advocates became Director-General of the British ordnance factories, a few years ago, that system of construction had only appeared on the firing ground and not in regular service. At present a certain number of the English guns are wire wound, and it is said that Russia is also making guns of this type. Undoubtedly greater circumferential strength can be obtained by using steel wire in place of hoops, but it is at the expense of comparative weakness longitudinally. Moreover, experience seems to indicate that neither less cost nor less time of manufacture result from the use of wire in gun construction, though these have been claimed as its special advantages.
Not only is the wire-wrapped gun more susceptible to damage from hostile fire, but it is less well adapted to withstand the tremendous shocks and vibrations of discharge than is the gun built up of comparatively few parts of great inertia. When first proposed, wire winding presented features of great advantage, but at present the size and quality of procurable steel forgings are such that the superiority of the wire wound over the built-up gun, either as regards strength, safety, or cheapness, is, at most, trifling, and probably non-existent.
As regards other methods of gun construction, it is not to be doubted that an efficient, cheap and reasonably safe gun can to-day be made of cast steel, or can be forged in a single piece, but the manufacture of such guns can only be defended on the score of cheapness and slightly greater rapidity of production, and they cannot be regarded as in any sense equal to the built-up gun; a single-piece gun can never be as strong and can never be as safe as one built up of forged steel parts, and we cannot afford to put the poorer article on our ships.
From 1880 to 1898 all our guns were designed with chambers of a size to take a brown powder charge of half the projectile weight, which gave a muzzle velocity of from 2,000 to 2,150 f. s., according to the length of bore, while the use of smokeless powder in the same guns added some 300 f. s. to the velocity, without increase of chamber pressure. It was not, however, inability to increase their power which held our guns stationary for so many years,—it was the disadvantages attending any further increase in the weights of powder charges.
The successful development of a smokeless powder made it practicable to take a long step in advance, and it was wisely decided to go at once to a size of chamber and length of bore suitable to smokeless powder charges approaching in weight the former brown powder charges for the same calibres. Accordingly the new model guns, with which all our ships now building are to be armed, were designed to give 3,000 f. s. muzzle velocity with chamber pressures of about 17 tons, and they have all given results on the proving ground which practically equal those predicted for them.
This means a muzzle energy 2j4 times as great as was developed by the old designs using brown powder, and from 60 to 70 per cent greater than that given by the old designs when they used smokeless powder. This great increase in power, as I have said, has come primarily from the substitution of smokeless for brown powder, but the chances are strongly against there being another similar advance. Smokeless powders are made from the most powerful explosives known, and while further improvements may be made in the direction of increasing their stability and uniformity, any further increase in their power must come from the discovery of a new order of explosives at present unknown to our chemistry.
Of course we can go on increasing velocities with smokeless powder, just as we could have done with the old brown powder, at the expense of increased weights of charge and accompanying increased chamber volumes and lengths of bore, but just as with brown powder we stopped at charges of half the projectile weight, so I think it likely that with smokeless powder we will not go far beyond the same limiting condition.
A few words in regard to the all-important subject of the keeping quality of our smokeless powder will not be out of place. The destruction of a great quantity of this powder at Mare Island a year or more ago was almost beyond doubt caused by spontaneous decomposition. Fortunately, however, there is reason to believe that the cause of that decomposition has been determined and has been removed by the enforcement of more stringent rules looking to the purification of the pyro-cellulose from which the powder is made. Heat tests alone used to be relied upon to prove that proper care had been taken in the processes of manufacture of smokeless powder, but it was found that certain conditions made these tests entirely unreliable, the result being that some insufficiently tested material was accepted and made into powder. It is believed that a repetition of the trouble will be prevented by the methods of inspection and test now in use.
Considering next "Rapidity of Fire,"—the time from fire to fire of any gun under service conditions is made up of two factors, "the loading interval," or the time from one discharge until the gun is again loaded and primed, and the "pointing interval," or the time it takes to get the gun on the target and fire it. It is the first of these factors, the "loading interval," that fixes the "rate of unaimed fire" which is determined on the proving ground, and which depends largely upon the perfection of the breech mechanism and of the loading apparatus.
During the entire course of the modern development of guns, from small arms to the largest cannon, it has been the constant effort of inventors in the field of ordnance to reduce the “loading interval” by mechanical improvements. Almost as constant has been the opposition, on the part of military men, to progress in this direction. It was, and still is, alleged that the “pointing interval” is what really determines the rate of fire in service, and that reduction in the “loading interval” really means nothing but increased waste of ammunition. It is not seen that the less the loading interval the greater the time which may be given to pointing the gun, and that the true way to prevent waste of ammunition is not by the use of imperfect weapons, but by the education of men to properly use perfected ones. In the days when clouds of smoke obscured the target and made the rate of any really aimed fire slow, the argument that there was plenty of time to load between fires, and that nothing could be gained by reducing the loading interval, was fairly plausible, though in fact the quicker the loading the less the chance of missing an opportunity of firing with good aim through the smoke, but now that smokeless powder has come into use it should be clear to all that every necessary second used in loading a gun is valuable time lost. Save ammunition by teaching the gun pointers to shoot, not by wasting time which is much more valuable than ammunition.
The extension of the use of metallic cartridge cases from the small arm to larger and larger guns has been the chief factor in the great reduction of the “loading interval” which has been made in recent years. Not only did the brass case permit the use of fixed ammunition, whereby projectile and powder charge are loaded in one motion and no subsequent priming is required, but it was also an efficient gas check, separate from the breech mechanism, so that the latter required no great power to open it. The ordinary forms of gas checks frequently stick after the gun is fired and so prevent the use of a quick-acting breech mechanism, which, operated by a single motion of the hand, has little opening power. The first small R.F. guns all had wedge breech closures, but as the advantages of the brass cartridge case were realized, and its use was applied to guns having the slotted screw breech plug, one after the other 4, 5, and 6-inch rapid-fire guns came into genera use, and the metallic cartridge case was even tried in 8-inch and 10-inch guns. Beyond the 5-inch calibre, however, the advantage of fixed ammunition cannot be realized, because the weight of a complete round becomes too great to be readily handled by a single man, and the moment that improvements in gas checks overcame the difficulty of sticking after each fire, the metallic cartridge case became only a useless extra weight which retards rather than accelerates the rate of fire of the larger calibres. With the 6-inch calibre, and even with the new, high-powered 5-inch gun, the suppression of the cartridge case and a return to the old-fashioned cartridge bag result not only in a considerable saving in weight and cost of ammunition, but also in an actual gain in rapidity of fire. Quick working breech mechanisms, however, which until recently could only be used with metallic case ammunition, are being constantly improved and further extended in use, and the name rapid fire gun has now come to designate any gun whose breech is opened and closed by a single sweep of the hand. In this sense our new 7-inch gun will be a "R. F." gun, but it would be better to call it a "quick fire" gun and to limit the name "rapid fire" to such guns as use metal cases.
Another improvement which helps us to suppress cartridge cases without loss off efficiency is a firing mechanism which allows priming with the breech open without danger of a premature explosion, and which automatically ejects the fired primer as the breech is opened.
I have just spoken of our new 7-inch gun as being a quick firing gun, as having a breech mechanism actuated by a single motion lever. This has been rendered practicable primarily by an improved gas check, but secondarily by the use of screw breech plugs having more than half their surface threaded. This improvement has been applied to all our guns from the 4-inch up, though it has greater and greater advantages as the calibre increases. Thus it enables the length of screw box and plug of the 12-inch gun to be reduced some 6 inches, which means, first, a saving in the weight and cost of gun; second, a lighter and more easily manipulated breech block; third, a more direct lead and ammunition hoist from loading room to breech; and fourth, a less diameter of turret with and cost of armor.
During the entire course of the modern development of guns, from small arms to the largest cannon, it has been the constant effort of inventors in the field of ordnance to reduce the "loading interval" by mechanical improvements. Almost as constant has been the opposition, on the part of military men, to progress in this direction. It was, and still is, alleged that the "pointing interval" is what really determines the rate of fire in service, and that reduction in the "loading interval" really means nothing but increased waste of ammunition. It is not seen that the less the loading interval the greater the time which may be given to pointing the gun, and that the true way to prevent waste of ammunition is not by the use of imperfect weapons, but by the education of men to properly use perfected ones. In the days when clouds of smoke obscured the target and made the rate of any really aimed fire slow, the argument that there was plenty of time to load between fires, and that nothing could be gained by reducing the loading interval, was fairly plausible, though in fact the quicker the loading the less the chance of missing an opportunity of firing with good aim through the smoke, but now that smokeless powder has come into use it should be clear to all that every unnecessary second used in loading a gun is valuable time lost. Save ammunition by teaching the gun pointers to shoot, not by wasting time which is much more valuable than ammunition.
The extension of the use of metallic cartridge cases from the small arm to larger and larger guns has been the chief factor in the great reduction of the "loading interval" which has been made in recent years. Not only did the brass case permit the use of fixed ammunition, whereby projectile and powder charge are loaded in one motion and no subsequent priming is required, but it was also an efficient gas check, separate from the breech mechanism, so that the latter required no great power to open it. The ordinary forms of gas checks frequently stick after the gun is fired and so prevent the use of a quick-acting breech mechanism, which, operated by a single motion of the hand, has little opening power. The first small R.F. guns all had wedge breech closures, but as the advantages of the brass cartridge case were realized, and its use was applied to guns having the slotted screw breech plug, one after the other 4, 5 and 6-inch rapidfire guns came into general use, and the metallic cartridge case was even tried in 8-inch and 10-inch guns. Beyond the 5-inch calibre, however, the advantage of fixed ammunition cannot be realized, because the weight of a complete round becomes too great to be readily handled by a single man, and the moment that improvements in gas checks overcame the difficulty of sticking after each fire, the metallic cartridge case became only a useless extra weight which retards rather than accelerates the rate of fire of the larger calibres. With the 6-inch calibre, and even with the new, high-powered 5-inch gun, the suppression of the cartridge case and a return to the old-fashioned cartridge bag result not only in a considerable saving in weight and cost of ammunition, but also in an actual gain in rapidity of fire. Quick working breech mechanisms, however, which until recently could only be used with metallic case ammunition, are being constantly improved and further extended in use, and the name rapid fire gun has now come to designate any gun whose breech is opened and closed by a single sweep of the hand. In this sense our new 7-inch gun will be a "R. F." gun, but it would be better to call it a "quick fire" gun and to limit the name "rapid fire" to such guns as use metal cases.
Another improvement which helps us to suppress cartridge cases without loss off efficiency is a firing mechanism which allows priming with the breech open without danger of a premature explosion, and which automatically ejects the fired primer as the breech is opened.
I have just spoken of our new 7-inch gun as being a quick firing gun, as having a breech mechanism actuated by a single motion lever. This has been rendered practicable primarily by an improved gas check, but secondarily by the use of screw breech plugs having more than half their surface threaded. This improvement has been applied to all our guns from the 4-inch up, though it has greater and greater advantages as the calibre increases. Thus it enables the length of screw box and plug of the 12-inch gun to be reduced some 6 inches, which means, first, a saving in the weight and cost of gun; second, a lighter and more easily manipulated breech block; third, a more direct lead of the ammunition hoist from loading room to breech and less space to load through; and fourth, a less diameter of turret with saving of weight and cost of armor.
With the 6-inch R. F. gun it takes less than two seconds to open and again close the breech, and a well-drilled crew can load in from 5 to 6 seconds, so that the "loading interval" is from 7 to 8 seconds, and, starting loaded, from 8 to 9 unaimed rounds can be fired in one minute.
The old 8-inch breech mechanism took about 10 seconds to open and close; with the new high-powered 8-inch gun this time will be reduced to about 5 seconds, and as the shell and charge can be inserted in 10 or 11 seconds, and the gun is primed during this operation, the loading interval will be about 15 seconds, and, starting with the gun loaded, it will be possible to fire 5 unaimed rounds in one minute.
These are the results of experiment on the proving ground, and there is no reason why they should not be equaled on board ship, excepting in so far as there is lack of space for rapid work in some of the 8-inch turrets.
With the larger calibres, new conditions come into play, and greatly increase the loading interval. Not only will weight of breech block and lack of space in turrets probably always prevent the use of a hand-worked single-motion breech mechanism on a 10-inch or 12-inch gun, but the necessity of using a mechanical rammer to push home their heavy projectiles, and the division of their powder charges into two sections, which have to be successively loaded, must always result in a marked distinction between their rate of fire and that of smaller guns. Improvements in ammunition hoists and in rammers have done much to reduce the time required to load the heavy turret guns, but still more can be accomplished by intelligent zeal on the part of those who actually handle the gun on shipboard. Thus, for example, the late Lieutenant Haesler materially reduced the loading interval of the Amphitrite's 10-inch guns by the simple expedient of having the two sections of the powder charge removed from the hoist while the shell was being rammed home, and loaded by hand the instant the rammer was withdrawn. Undoubtedly, the loading interval of heavy turret guns, even more than that of small guns, depends very greatly upon the skill with which their loading appliances are handled, and can only be reduced to a minimum by constant practice.
It takes about 9 seconds to open and close the breech of the new 12-inch gun fitted with our hand worked mechanism, which is, in my opinion, the most efficient one in existence, and to re duce this to the time required with a rapid-fire gun, we must resort to the automatic operation of the breech mechanism, which, moreover, besides reducing the loading interval by some 7 seconds, will reduce the number of men required for working the gun and will furnish a perfect protection against the danger of a hang fire, since the breech cannot open until the powder charge has exploded and caused the gun to recoil.
Coming now finally to the "pointing interval," which with the "loading interval" makes up the time from fire to fire under service conditions,—this has evidently been greatly reduced on the average by the use of smokeless powder, but is still a very variable quantity, depending not only upon the skill of the gun pointer and the efficiency of the pointing mechanism, but also upon the state of the sea and other changing conditions. In so far, however, as the pointing intervals of guns have been reduced in recent years by mechanical improvements, it is by improved gun mountings that the saving of time has been effected, and, as far as heavy gun mountings are concerned, the successful use of electricity for manipulating them has been the chief cause of the saving of time. Steam, and especially hydraulic machinery, for working heavy gun turrets, will not give the smooth, steady, and perfectly controllable motion so necessary for pointing at a moving target, but electric motors do. As far as the mounts of rapid-fire guns are concerned, the ease and rapidity of motion which can be attained when they are handled by practiced men leave little to be desired.
The ideal gun mounting would be one with which the line of sight of the gun could be kept constantly upon the target, regardless of the motion of target and of gun itself, and with such a mounting the pointing interval would disappear and the rate of aimed fire equal that of unaimed fire. We are, of course, far from attaining this state of perfection but we are gradually approaching it. Even to-day it depends wholly upon the skill of the gun pointer, only to be acquired by practice, whether the rate of well-aimed fire of any gun shall be a maximum or shall be only a small fraction of what it should be.
The enormously greater destructive power of modern projectiles than those used 50 years ago results from these two things,—1st, hollow shells filled with explosives have replaced solid shot, and 2d, the rifle principle enables us to use elongated projectiles, weighing four times as much as the old spherical ones, and which, traveling point first, can readily be caused to explode by impact. One of the most important and pressing ordnance questions of to-day is to determine the character and arrangement of explosive charges which will make shell most destructive. We use fine-grain black powder for our bursting charges; should we replace it by a high explosive?
Merely stating that in my opinion the so-called "torpedo shell," designed to throw great quantities of high explosives, has necessary disadvantages which outweigh its possible advantages as a projectile for naval use, I shall only consider such projectiles as are suited to be fired with high velocities from the latest type of naval guns. Such projectiles may be roughly divided into the two classes of "thick walled" and "thin walled" shell, according as they are or are not designed to have any armor-piercing qualities.
Considering first "thin walled shell;" these can carry, as a maximum, bursting charges of black powder weighing about ten per cent of their total weight. For these charges can be substituted a somewhat greater weight of a high explosive,— gun cotton, picric acid, lyddite, melinite, or what not,—but to get good explosive effect, each of these compounds must have a fulminate detonator associated with it. If strongly confined and merely ignited by an ordinary percussion fuse, they produce a violent explosion, but the confinement in thin walled shell is insufficient for this as a rule. The lyddite shell used in the Soudan and South Africa were fitted in this way, and such a large percentage of them failed to burst, merely breaking open, and the greater part of the contents remaining unexploded, that they were considered a total failure and looked upon rather with contempt by those against whom they were directed. If, on the other hand, such shell are fitted with fulminate detonators, their explosion produces much more complete fragmentation and a much wider cone of dispersion than does a gunpowder shell. It must not be supposed that the shock of the explosion counts for anything in the damage done. Outside of the poisonous effects of the gases and the direct action of the flame, it is the projected fragments which cause what destruction there is. A powder bursting charge will break a thin-walled shell up sufficiently, but the fragments do not spread much. The detonation of a high explosive charge produces a much wider cone of dispersion, and therein lies its greater destructive effect. Moreover, the action of the detonated shell is much quicker than that of the one burst by ignited powder,—the former bursts almost at the point of entrance and its fragments are sometimes driven through the deck above or below it,—the latter ranges from 10 to 20 feet before it bursts, and its fragments continue on in a cone of not very great angle. On the other hand, the high explosive shell is more likely than the powder shell to explode harmlessly outside,—either of them is completely ineffective if its impact is against even the thinnest armor, but the former is liable to burst before it gets through skin plating which it strikes at an angle. Finally, the detonating shell is vastly more dangerous to use than the powder shell,—premature explosions of each will sometimes occur; and while the worst effect of the latter is then to mar the gun, that of the former may be to burst it with demoralizing results.
But now, having weighed the relative advantages and disadvantages of thin-walled detonating shell as compared with the same shell loaded with powder, and supposing that we decide for the former, we have still to consider this question,—Is it desirable to have a class of projectile which is only effective against the entirely unarmored parts of ships,—is it not better to sacrifice explosive effect in all shell to gain power of penetration? All armored ships of recent construction have their vulnerable parts covered at least with thin armor; modern practice tends more and more to distribute, not to concentrate, armor.
Certainly it seems to me that the guns of armored ships, whose prime function is the attack of other armored ships, would much better use only thick-walled shell than attempt to produce greater destructive effect by hits upon unarmored parts.
As for the guns which form the main batteries of unarmored ships, since these cannot be expected to be opposed to armor, it may well be that their effectiveness would be increased by the use of thin-walled detonating shell, and the question, whether or not the attendant dangers should be accepted, needs careful consideration. One thing, however, we may feel sure of, and that is that there is no such vast and overwhelming superiority of the high explosive over the powder shell as is popularly supposed to exist.
Considering next "thick-walled shell," and including under this title both regular armor piercing shell and what are known as semi-armor piercing shell, let me first point out the fallacy of the idea that any sort of delay-action fuse is necessary to enable such shell to carry bursting charges through armor. If the charge is of a nature not to detonate on impact, as gunpowder, picric acid, wet guncotton, melinite, or lyddite, but is ignited by the shock of impact, it takes enough time for it to get up pressure to burst a thick-walled shell to enable that shell to perforate all the armor it is capable of perforating before the burst takes place. We know that a heavy shell fired through structural steel plating ranges some 20 feet before it bursts from the action of a percussion fuse and a black powder charge. This means a time interval from impact to burst of say 1/100 of a second. Now suppose a 12-inch shell, strong enough to go through unbroken and without serious distortion, to strike a 12-inch plate with 2,000 f. s. velocity, and to just get through it. Its mean velocity would be about 1,000 f. s., and so it would take it only 1/1000 of a second to perforate the plate. Actually it would have some remaining velocity, and so the interval would be less, but the rough comparison is enough to show that the time to burst is much longer than the time to perforate. It is only when the shell is either broken or much upset by impact with the armor that its explosive charge cannot be carried through and exploded behind the armor. This was demonstrated at our Proving Ground years ago with black powder by firing fused 6 pdr. a. p. shell through 3-inch steel plates, when they burst after just perforating the plates, and by firing a 10-inch semi a. p. shell, loaded with 20 odd pounds of black powder, and fused, through a 7-inch hard faced plate when it burst several feet beyond the plate. It was also proved with jovite, a picric acid compound, just as are melinite and lyddite, by firing a 10-inch a. p. shell, filled with that explosive and with an ordinary percussion fuse, through a 14-inch hard faced plate, and bursting it behind the plate.
We do not, as yet, load our a. p. shell, but there is no difficulty in the way of doing so. Black powder will not always burst such shell, and so it may be better to load them with picric acid, jovite, a fine-grained smokeless powder, or some other substance which, when ignited with an ordinary percussion fuse, and being strongly confined, will not detonate, but explode. The certainty of the shell, if it gets through armor, being broken into pieces, and not remaining whole, would be worth a good deal even if the explosion itself were of little violence.
Under these circumstances, then, the problem as regards thick-walled shells resolves itself into this,—shall we be content with a moderately powerful explosion of each shell behind armor or anything else they can perforate, or shall we attempt to make them detonate? If the latter, there must not only be a fulminate detonator in each shell, but also some sort of a delay action for that detonator, since otherwise the detonating action, being vastly more rapid than that of explosion by simple ignition, would cause the shell to burst harmlessly outside of any armor it might strike. All this I believe to be perfectly practicable, and again it is merely a question of expediency. We must weigh the relative advantages and disadvantages and decide whether or not the somewhat greater destructive effect of the detonating shell is worth attaining at the expense of its greater complications and its greater danger to ourselves. The Ordnance Department of the army have decided in favor of high explosive shell charges upon grounds which do not altogether apply to the navy. With their use of high angle fire from shore batteries, the sphere of action of the high explosive shell of large capacity is considerably increased by the torpedo effect of an underwater burst,—with the flat trajectories needed in naval actions such an effect cannot be expected.
There was considerable complaint made of the inefficiency of our common shell, as instanced by many failures to burst observed in the bombardments at Santiago. These failures were due to the fact that our base percussion fuse was developed by experimental firings through thin steel plates, such as form the skin plating of ships, and, while sufficiently sensitive to be exploded by the impact of the shell upon such plates, was not sensitive enough to explode when the shell struck comparatively soft earth. This experience has led to the substitution of a much more sensitive percussion cap for the one formerly used in fuses; but that our shell, even before this change, were effective when used against ships, the results of the battle of Manila Bay and Santiago sufficiently testify.
The following description of the effects of 12-inch common shell which entered the Reina Mercedes when the Spaniards were trying to sink her in the channel of Santiago on the night of July 6, 1898, will give an idea of what destruction such a shell may cause. It entered the port quarter, burst 18 feet inside, and after ranging 120 feet, the central fragments passed out through the starboard bow. A hole 6x3 feet was blown down through the main deck and a number of fragments entered the engine room, where they cut several steam pipes and ripped the lagging completely off the top of a boiler. A machine shop and dynamo room built around the main mast was completely demolished, everything in it being destroyed, and the mast itself was cut in two by a fragment and dropped vertically 4 inches, slacking up all the rigging. A number of large holes were cut through a bulkhead surrounding the smokestack and uptake and they were pierced with many holes, both safety valves being knocked off and two steam pipes cut. On both sides, on the decks above and below, and in beams and stanchions, were numerous cuts and dents showing where fragments had struck, and it may fairly be said that one such shell, in actual battle, would have swept the deck clear of men and practically put the ship out of action.
The effects of gun fire, however, depend not only upon the action of the shell which has reached its mark, but upon the power which enables it to get to its mark, upon the number of shell fired, and upon the percentage of hits. We have seen that the great mechanical improvements in ordnance material in recent years have tended largely to increased rapidity of fire, and that the use of smokeless powder has not only greatly increased the penetrative power of projectiles, but also enables us to attain under service conditions a rate of fire approaching that obtained on the proving ground. But it is in the small percentage of hits that naval gun fire falls short; destructive power there is and rapidity of fire, but accuracy of fire is still greatly lacking. At the battle of the Yaloo the Chinese battleships fired 197 12-inch shell and but 7 of them hit Japanese ships, and lest we attribute is to special inefficiency, let us remember that our own percentage of hits at Santiago was only about 4. Now it is not the gun which is here at fault. With the distance known, a modern gun fired from a stationary platform will put every shot in a 10-foot square target at 2,000 yards. The trouble is three-fold. Supposing the sea to be perfectly smooth, there are two important causes of error, the first due to incorrect estimation of the distance of the target, and the second due to imperfections in the sighting mechanism.
No satisfactory range-finder has yet been introduced into our naval service, and though the flat trajectories which result from the high velocities given by the latest type guns reduce the errors of gun fire due to lack of correct knowledge of distance, yet these errors are still large. In the second place, there is a considerable error in pointing guns caused by the inability of the eye to determine with certainty when the rear sight, the front sight and the distant object are in line; consequently, when the gun pointer fires, thinking his gun is correctly pointed, he is usually considerably in error. The telescope sight largely removes this difficulty. But even if we had perfect range-finders and perfect sighting apparatus, the greatest cause of error would still remain. The pitch and roll of the ships, due to the never-ceasing motion of the sea, disturbs the line of fire during the interval between the gun pointers willing to fire and the actual departure of the projectile from the muzzle. Not only is there a perceptible time between the pressing of the electric key which fires the primer and the exit of the projectile from the gun, but there is much greater interval between the time when the gun pointer wills to press the key and the time when he actually does so. This latter interval, called the personal equation of the gun pointer, is said to be 3/10 of a second on the average, and during this period the roll of the ship causes a considerable change in the elevation of the gun and thus causes a projectile which would otherwise hit the target to pass far above or below it. The marksman's skill lies principally in making proper allowance for his personal error, but, under the constantly varying rate of angular motion, this can never be done with any great accuracy, and thus under ordinary conditions of gun practice at sea the percentage of hits is always very small.
Further increase in the destructive effects of naval gun fire must come rather from increased skill of the gun pointers than from any improvements either in guns or in their projectiles.