Translated by LIEUT.-COMMANDER STEPHEN V. GRAHAM, U. S. Navy, from Revista General de Marina.
The selection of the gun that is to form the main battery of a battleship is a problem that is to be solved by the artillerist, the sea-going officer, and the naval constructor, since these three occupy different points of view which it is necessary to embrace and harmonize, in order to arrive at the correct solution.
At the present moment there exists a strong current of opinion in favor of an increase of caliber, as shown in the armament of the most recent ships of the principal naval powers.
England initiated the movement, for, while the Dreadnought mounted guns of 45 calibers in length, and the St. Vincent 12-inch of 50 calibers in length, the Orion class will carry 13.5-inch guns of 45 calibers in length.
In the United States the same course has been followed, and, while the 14-inch guns of 45 calibers form the main battery of the New York and the Texas, it is said that a 16-inch naval gun is in the experimental stage. Germany, for her part, has advanced rapidly from 11 to 12 and 14 inches.
As is seen, all of the powers are increasing the caliber of their heavy guns, and the 13.5-inch gun appears to be giving place to the 15-inch and 16-inch gun. Nevertheless, some naval authorities indicate the probability and desirability of the return to more moderate calibers, or, at least, experience some doubt as to the maximum efficiency to be obtained in naval vessels by the use of such exaggerated calibers. Even Brassey's Annual, so enamored of English ideas, in its last edition, states that it is not easy to predict the size and power of the gun that will prevail.
It is not, as might appear at the first view, the progress in armor which has primarily necessitated the increase of caliber, for precisely during the time that armor plate has, so to speak, remained stationary, calibers have been increasing.
Discounting the possibility of superior armor to be obtained in the near future, as seems to be indicated by the results of tests of the Simpson plates, there exist other powerful reasons for such increase, which we are going to expose, together with proportionate views of the other side of the question.
We will consider in the first place the penetrating power of the various guns, and, estimating the usual battle ranges to be those comprised between 4000 and 7000 meters, we present the following table from an article read by Count Giraldi, director of the Armstrong factory at Pozzuli, at the first Congress of the Society of the Italian Naval Architects and Marine Engineers, held at Rome, in the middle of last November.
Range | Model 1910 12-inch projectile, wt. 972 lbs., 50 cal. | 13.5-inch projectile, wt. 1245 lbs., I. V. 2500 f. s., 45 cal. | 14-inch projectile, wt. 1566 lbs., I. V. 2500 f. s., 45 cal. | 15-inch projectile, wt. 1930 lbs., I. V. 2500 f. s., 45 cal. | 16-inch projectile, wt. 2343 lbs., I. V. 2500 f. s., 45 cal. |
Yards | Inches | Inches | Inches | Inches | Inches |
4364 | 16.1 | 17.1 | 18.15 | 19.5 | 21.1 |
5357 | 15.4 | 16.3 | 17.1 | 18.6 | 20.15 |
6547 | 13.5 | 15.3 | 16.2 | 17.7 | 19.3 |
7638 | 12.6 | 14.3 | 15.35 | 16.9 | 18.5 |
This table shows the thickness of plates of Krupp armor which would be penetrated upon being struck normally by the projectiles of different calibers at ranges between 4000 and 7000 meters, which ranges appear to be the greatest at which it is advisable to fight with armor-piercing projectiles.
Examining the table it is seen that, in some cases, the penetrating power, with relation to the caliber of 12-inch, increases even as much as fifty per cent, and that an effective increase of twenty per cent can be counted upon, which affords a good margin for future armors of resistance superior to the present Krupp plates. And so much more advantage is obtained, if we have, for example, a 12-inch projectile attacking with success under given conditions, a 13.5 inches thickness, since the penetrating power increases much more rapidly with an increase of caliber than the resistance of a plate increases with analogous increase of thickness. Since the thickness of armor cannot be increased indefinitely, there will always be, using superior calibers, an excess of penetrating power over the resistance of armor.
We have considered only normal impact, which cannot be counted upon in naval actions; and penetration diminishes with the increase of incidence, until it becomes nil, so that, from this point of view, not much greater results would be obtained by at- tacking with a heavier projectile resulting from an increase of caliber. For this reason, and because present battleships, as well as those under construction, are protected by a belt of 11.8 inches thickness, which can be penetrated by a 12-inch gun, Count Giraldi recommends not increasing caliber beyond this limit.
At present there is a general tendency in all navies to reduce in number the variety of projectiles to be used, pursuing the ideal of arriving at a "single type" which will satisfy all the exigencies of a modern battle; that is to say, which will possess sufficient penetrating power united with greater destructive power by the explosion of its charge.
The French Navy has led in this movement with its obus alourdi (weighted shell),'designed to combine the effects of an armor-piercing shell of large capacity with walls of sufficient thickness to resist impact, pierce armor of medium thickness, bursting behind it by the action of its large charge and the delayed action fuze with which it is equipped.
The increase of caliber also favors the realization of this ideal by making it practicable for projectiles to carry a large quantity of high explosive, the utility of which was demonstrated by its destructive effect in the Russo-Japanese war.
In fact, the weight of a projectile increases rapidly with the caliber; the weight of the explosive charge and the destructive power increasing consequently in equal proportion. The current technical opinion is that a 12-inch projectile of the approximate weight of 990 lbs. can carry an explosive charge of the weight equal to 3 per cent of the total, that is 29.7 lbs., without losing, on this account, any considerable amount of its power of penetration. It does not appear unreasonable to suppose that a 14-inch projectile, with a weight of 1540 lbs., can carry 3.5 per cent of its plate of 12 inches in thickness. A 13.5-inch projectile will penetrate with more ease under the same conditions a plate of weight, or 54.1 lbs., of explosive. No more does it appear excessive to admit that a 15-inch projectile, with a weight of 1760 lbs., will carry4 percent of explosive, that is, 70.4 lbs., and, if it is considered that the high explosive shells (when such are provided in addition to purely armor-piercing shells) carry a bursting charge of 75 per cent of the total weight of the projectile, we have in the case of the 12-inch high explosive shell a bursting charge of 74 lbs., which is practically the weight of the bursting charge of an armor-piercing shell of 15-inch caliber. From this it is seen that with this caliber the ideal of the above-mentioned "single type" of projectile is realized.
In the paper above mentioned, Count Giraldi attempted to prove the contrary, claiming that the armor-piercing shell of to-day carries a bursting charge of 2 per cent of its weight, and that, even if the projectile of the" single type" could increase this to 3.25 per cent, or 3.5 per cent, this limit could not be exceeded; and, therefore, in order to obtain the 74 lbs. of the present 12-inch semi-armor-piercing shell, it would be necessary to increase the caliber to at least 16 inches. For this reason he considers the adoption of a projectile of the "single type" as very doubtful; and when it is further considered that modern high explosives are much more powerful than those of the past, it appears to him unnecessary to increase the caliber above 12 inches, with a length of 45 or 50 calibers. It is true that a projectile from such a gun (12-inch) is capable of destroying the superstructures of an enemy's ship, but it is also true that no vital parts of a ship are situated behind the superstructures.
There are, in addition, other important reasons for advocating an increase of caliber, among which is the very important one of erosion of the bore.
It is true that great effects may be obtained with relatively small calibers, but it is always at the cost of wearing down of the metal and the erosion produced by large charges of nitro-glycerin powders (almost universally used) in spite of the favorable conditions under which these are manufactured at present, the temperature of explosion being reduced by the addition of hydro-carburates. This aspect is very interesting, not only for economic, but also for military reasons, since the erosion suffered by the rifling, and in one word, the bore, diminishes the force of projection and density of loading (by advancing the projectile into its seat), affecting sensibly the precision of the weapon and diminishing the number of rounds of which it is capable, which might be of grave consequence in a campaign.
Also, since superior caliber provides for a projectile of greater weight, the muzzle velocity may be reduced a given amount and still maintain the same striking energy, and this increases considerably the life of the weapon. However, with these guns the trajectories are less flat than with a gun of 12-inch caliber, which is not desirable in naval gunnery. Consequently, it is advantageous to increase the muzzle velocity in such degree as not to lose advantage of the greater life of the gun and yet obtain a trajectory with a maximum ordinate which will satisfy the necessities of naval combat.
For this reason the 14-inch gun of the United States was given originally an initial velocity of 2580 feet per second, and there is a tendency to increase this to 2680 feet per second.
Another advantage of the larger calibers is the moral effect they impress upon the men who serve them, since they are beyond doubt more impressed with the power of the individual gun they are serving than with the number of guns which their ship carries, and they will be more confident and more certain of victory if they are firing guns that are more powerful than those of the enemy, or, at any rate, those that equal the guns of the enemy. Incidentally it should be mentioned that the ammunition supply is simplified; the direction and control of fire is facilitated; first because the impact of larger shells is more easily seen, and, also, for a given displacement there are fewer guns to control. This has, however, a serious disadvantage, which will be mentioned later.
The advantages and disadvantages of the increase of calibers above 12 inches having been analyzed, we will touch in passing, upon the problem of these most important installations.
We will consider the number of guns that a battleship can mount, taking 20 per cent of the displacement as available for armament. Deducting the 2 per cent necessary for secondary battery, there remain 18 per cent for the principal installations,
so that, since the complete weight of the armament of ten guns, including 120 rounds of ammunition for each, amounts to 3250, 3950, and 4750 tons, according as the guns are of 12-inch, 13.5 inch, 14-inch, respectively, we are brought to displacements of 18,000, 22,000, and 26,500 tons, as the case may be. If it were desired, for example, not to exceed 22,000 tons displacement, it would be necessary to renounce mounting 14-inch guns if we wished to install ten large guns.
With the displacement mentioned a ship could carry twelve guns of 12-inch, ten of 13.5-inch, or eight of 14-inch. These figures throw doubt upon the advisability of exceeding a caliber of 12 inches, since the offensive power being thus concentrated in so small a number of pieces (eight if 14-inch caliber be adopted) it is much to be feared that a casualty would disable an important aliquot part of the armament.
As to the type of turret to be selected, double or triple, there are authorities who assign to each gun of 12-inch caliber a weight of 250 tons in the first case, and 150 tons in the second, which shows an important economy of weight amounting to one gun in ten, in case triple turrets are used.
Certain English and Italian publications claim that the saving of weight is even greater.
The triple turret has the further advantage of requiring a less numerous personnel and of simplifying fire control. But it possesses the disadvantage of a greater turning moment when the side guns are fired, and the accumulation of gases.
Italy has been the first nation to launch a battleship carrying triple turrets; but, as Sir William White says, the sanction of this practice depends for proof upon rapidity of loading and firing, and there still remains the risk of disability of a large number of major guns at the same time.