GUNNERY AND TURRET DESIGN
By Commander H. F. Leary, U. S. Navy
Naval gunnery is the science and art of using guns at sea.
As a science, it deals with the motions of projectiles, elucidates the laws which govern their deviations; determines the probability of their attaining the objects aimed at and calculates their effect.
As an art, it is concerned with the actual handling of guns and studies how to obtain accurate and rapid fire from a single gun and how most effectively to combine the fire of a number of guns.
It is the art of gunnery which should principally concern the naval officer, the highest object of whose ambition it should be to make the fire of the guns under his command, whether a single gun, a turret, a ship's battery, or the combined batteries of a squadron, the most effective possible.
The theory of gunnery, except in an elementary way needs but the attention of the specialist; the practice of gunnery is essential to the efficiency of every naval officer, and may almost be said to be his proper life-work.
It is the gun which is the determining factor in naval actions, and to the gun everything else should be subordinated in the design, construction and tactics of warships. The other features of men-of-war have no raison d’être except in so far as they serve to bring the guns into action and to maintain them there. Protection to buoyancy and stability is merely for keeping the battery afloat, and protection to guns and men is merely for maintaining the battery in operation under hostile fire; coal endurance and speed are merely for extending the battery's field of action. All these things give endurance and power to the battery. The essential object of the officers and men too, from the commander-in-chief down, is to use the ship's batteries. The fighting efficiency is measured by their ability to do good work with the guns which they control. They may one and all be at the highest point of efficiency in every other branch of their profession, skilled in seamanship, and in navigation, linguists, well versed in military and international law, and all these things may avail them nothing in that decisive hour of battle, for which their lives should be a preparation; then it will depend primarily upon their skill in gunnery, upon how effective the gun fire of the ship or of the squadron is, whether they shall triumph or go down to merited and perhaps even disgraceful defeat.
The efficiency of every warship in the last analysis is the efficiency of her battery, and it is the highest duty of every officer on her, and above all her commanding officer, who is responsible for her efficiency, not only to see that the best possible results are obtained from the material on board, but also to see that defects in material and equipment are remedied, and that any possible improvements are recommended for adoption. Of course there will always be defects in our ordnance material, but they can only be remedied and improvements made through the co-operation of the officers who are using them with those who control their design and construction. If we are to hope for steady progress towards perfection our Bureau of Ordnance must be ready at all times to make changes which are real improvements, and at the same time those afloat, while unremitting in urging improvements must do their utmost with what they have, and not assume the attitude of the poor workman who blames his tools for his bad work. There will always be questions in ordnance about which there is difference of opinion, even among those best qualified to pass opinion, but the freest possible discussion, and honest constructive criticism of ordnance designs and gunnery methods cannot but lead to marked improvement.
It may be well to start with a short summary of the progress of gunnery in our navy, in order to show how from year to year the requirements have progressed and the demands for improved material have produced the changes desired and have led to the adoption of our present equipment. The Ordnance material and methods in use at the time of the Spanish war were for that day considered excellent, and it is doubtful if at that time our turrets or methods were surpassed in the British, French, or German navies. After the Spanish war, however, in considering the lessons learned and the needs in ordnance and gunnery, for our modern navy, a marked change took place. Officers in our service began to realize that the types of target practice then in vogue, and the general battle conditions which our material should be called upon to meet were not in accord; that the practices did not create sufficient interest on the part of officers and men, did not test the ordnance material to the extent necessary, nor were the practices so difficult as to create a demand for improved equipment. It is interesting to note that in March, 1900, the commanding officer of the Amphitrite submitted to the Bureau of Navigation recommendations regarding a uniform system of gunnery instruction based on the experience of that vessel as a gunnery training ship and it is quite remarkable to note the many points considered at this time which are now current practice in gunnery training. Based on these recommendations, the Bureau of Navigation issued General Order No. 9 of September, 1900, covering gunnery instructions for cruising vessels. This was the first real start on systematic gunnery training. About this time, Admiral Sims, then a lieutenant who was on the Asiatic Station, recommended sweeping changes in the methods of gunnery training then in force, based on information obtained from methods being tried out by the British. He, in conjunction with several officers of that station, made alterations in gun sights, bought telescopes, and requested a new system of target practice, based on his ideas of the proper methods for gunnery training. A strong appeal was made to the Navy Department to institute some such system of target practice for the whole navy. This was done by President Roosevelt; and Admiral Sims was appointed as Director of Target Practices. There was a great deal of opposition on the part of a number of the officers to such radical changes; a great many thought then, and there are some who now think, that it is unnecessary to have competition in order to produce efficiency. In 1903 Professor Alger wrote his prize essay on "Naval Gunnery," an extract from which is quoted at the beginning of this article. In March and April, 1903, the Atlantic fleet took up this new system of target practices and held them off Pensacola, Fla. On board the old Texas (San Marcos) Captain Nulton, then gunnery officer, developed a fire-control system and various schemes of checking sight setters, sending ranges, spotting and analyzing results; and, strange as it may seem, the methods of analysis now in use in the fleet are not very dissimilar from these early efforts. At the first target practices, held off Pensacola and on the Asiatic station, the results were very good considering the material. It was shown, however, that changes would have to be made in methods of handling our ammunition, graduating sights, and in the systems of obtaining and transmitting the range. During the following years, everyone was keyed up on the subject of gunnery. Gunnery instructions were issued in 1905, explaining in detail the new system, showing how the training should be conducted and giving the principles of the elementary fire control then necessary, and how the practices should be conducted.
As the result of several years work it was demonstrated that turret arrangements were not safe; this was evidenced by the Massachusetts explosion in an 8-inch turret in 1903; the explosion in the after 12-inch turret of the Missouri in 1904; an explosion in the 13-inch turret of the Kearsarge in 1905, and again on the Georgia in 1907 (8-inch turret). It began to look as if the navy could not hold a target practice without some terrible casualty. Everyone in the fleet was doing his utmost to make his turret, battery and ship shoot fast and hit. Some mistakes were of course made in the handling of material, but on the whole it cannot be said that the unfortunate accidents were wholly the fault of the personnel. We learned by bitter experience, and it is most fortunate that the efforts made by a few misguided officers to have the practices abandoned were not successful.
The explosion on the Missouri brought about the installation of the gas ejector system, flame shutters between the turret chamber and handling room, and the two-stage turret hoists fitted on all ships from the Michigan class on. It became known what a "flare-back" might do. The accident on the Massachusetts brought about precautions in regard to opening the breech plug, and improved designs of firing locks; that on the Kearsarge called attention to the danger of exposed switches in the turret in rear of the breech; in fact, the present "Safety Precautions" were built up on lessons learned in those days, and to those of us who followed the game each precaution has its own history.
In 1907 at the time of the cruise around the world, a Turret Board was ordered to make a thorough investigation into the defects and needs of the navy, regarding turret design and construction. General recommendations were laid down which should guide the Department and Bureau of Ordnance in the design and operation of turrets. These continued in effect, being revised from time to time, until the recent revised Turret Board's report of 1919. It is rather surprising to see that in the period of 10 years, from 1907 to 1917, the general principles of turret design and construction had not changed as much as one would expect. The developments led to the introduction of the two-stage hoist and three-gun turret, but the general requirements remained much the same. It may also be noted that after the investigations made by the Turret Board in 1907, and due to the various precautions put into effect, and the modifications made to nearly all turrets, but few accidents have happened. Meeting the demands of the fleet, the officers in the service themselves devised and superintended the manufacture of improved sights, breech mechanisms, and turret gear; and also outlined the methods necessary adequately to serve and control the guns. The "Ship and Gun Drill Book" was prepared by a board of experienced turret and battery officers. In 1913 the "Gunnery Instructions" were revised and the manual now in use (1920) is based mainly on this work.
The fact that the above results were not all done earlier is not considered as a criticism upon the officers in the service prior to 1900, nor of the ability, desires, or work of the navy at that time. With the small amount of money and lack of attention given to the navy during this period by Congress, and the few new ships authorized for a more modern navy there was not the opportunity or incentive to make such strides' as have existed since then. So from the Spanish War up to the present time the navy has expanded in every direction, and the forms of gunnery exercises have kept pace with the world's leading navies; ever making greater demands for improved methods and material. Especially since the beginning of the last war, the service has constantly had before it the question, "Are we equipped with the best material and using the best methods that can be used for action?"
Just because a ship does well at target practice is no absolute criterion of her readiness for battle, and in the battle efficiency inspection begun in the fleet by Admirals Fletcher and Badger, and perfected by Admirals Mayo and Grant, many ships were found that were not entirely ready for battle; and it was found that not all the material in use was sufficiently adequate in type or quality successfully to compete with the British or German navies in a modern naval engagement. After much argument in 1915, rules were formulated to open fire at long range (18,000 yards). This change was urgently recommended by Admiral Fletcher, then commander-in-chief of the fleet, and put in the Rules by a committee from the fleet, of which Captain Kearney was the head, as fleet gunnery officer. The results were most gratifying; since then the fleet has felt confidence in its ability to open fire at the maximum range of its guns, and turret designs were changed to give increased angles of elevation of 30° for vessels of the Tennessee class and 40° for the 16-inch 50 ships caliber. The recent improvements in design have included the adoption of a quick-acting breech mechanism for turret guns in which the motion of translation of the plug has been eliminated, and the closing is effected by an air cylinder, very little power being required as the weight of the breech block is taken by counterbalance springs. All turrets since the Michigan have been fitted with chain rammers, which are a material improvement over the old telescopic rammers, with their wire cables, which were a frequent source of casualties. In all new designs, the powder and shell supply to the guns has been separated, and the vertical reciprocating shell tube is now the standard in all modern turrets, the powder supply being either by a reciprocating car or a conveyor type hoist. The design of gun trunnions has been improved materially of late and is now considered as being entirely satisfactory as regards reduction of friction and self-lubricating features. The period during the war has witnessed the general introduction of the director system of firing, and this system, for both main and broadside batteries, has now been adapted as the primary system, as opposed to the old system of pointer fire. The advantages are many and well known, and due to the extreme difficulties of target designation, and of seeing the target at long ranges, and through smoke, splashes from enemy shorts, etc.; the use of aloft directors has become general. The demands of concentration firing, aeroplane spotting and use of kite balloons have also added some minor changes. The increase in battle ranges has led to the adoption of the pneumatic recoil and counter recoil system, as the spring designs were unsatisfactory for returning guns to battery at the high angles necessary. It is believed that the above covers in a general way the features of importance, that have been brought out by gunnery development, and we will consider the question of turret design in general terms.
About 12 years have elapsed since the construction of the dreadnought was decided upon, and this period has witnessed the developments in the design and armament of capital ships, which may be taken to cover the progress of modern armament, as the revolutionary changes introduced at that time furnish a definite starting point. The plans of this type of ship introduce a new governing principle into battleship armament, which has become known as the "all big gun," or "single caliber" armament in contradistinction to the previous type of armament. The former policy of installing a mixed battery with generally four guns of the heaviest type, and a large number of intermediate and secondary guns, was due to the erroneous belief that it was not advisable to increase the number of heavy guns due to the large increase of weight involved, and the low rate of fire from these guns. The intermediate guns by their great volume of fire, were considered more effective against the personnel and upper works of the enemy, thus silencing his fire. It has been definitely established as a result of target practice, that the heavier the projectile the more accurate the shooting will be, and as the standard of gunnery efficiency is "rapidity of hitting," the "all big gun," "single caliber" ship has become recognized as affording the maximum of effectiveness. Additional reasons for this type are: the amount of armor that can be installed on a ship being limited, it is impossible to assign sufficient weight adequately to protect a long broadside of intermediate guns against the fire of heavy guns; also the presence of smaller guns reduces the rapidity of fire, hence the effectiveness of large guns due to the interference in the fire control arrangements. Modern vessels are now being successfully armored against the fire of small guns and the personnel will be behind this armor; thus the small gun will be useless except for defense against torpedo attack. The high state of development to which gun and torpedo fire have, been brought has also led to an increase in the probable future battle ranges, again militating against the use of small guns. The selection of the caliber and type of gun for the primary armament of a battleship is a problem still open to great controversy. At the present moment there exists a fairly strong current of opinion in favor of increase of caliber, as shown in the armament of the most recent ships of the principal naval powers. This general change of opinion which has taken place relative to primary armament is to be attributed in part:
- To the increase in battle ranges.
- To the improvements in ship protection.
- To the practice of filling armor piercing projectiles with high explosives.
The increase in battle ranges and the improvements in armor both necessitate an augmentation in the striking power of the battery. There are several ways of accomplishing the desired result:
- By an increase in the caliber of the gun.
- By an increase in the weight of the projectile.
- By changing the shape of the projectile to obtain better ballistic qualities.
- By increasing the initial velocity.
(1) It has been demonstrated by actual firing that a gun of larger caliber, having a moderate initial velocity is able to fire a far greater number of accurate rounds than a gun of smaller caliber having a high velocity. Thus, since for the same velocity, at the same range, the penetration increases with the caliber, for a given penetration, the greater the caliber the lower the velocity, and the longer the life.
(2) If the weight of the projectile is increased, while the initial velocity remains the same, a greater amount of energy is obtained by an increase in the weight of the charge and an increase in the maximum pressure, which means an increase in the erosion of the gun equivalent to a diminution in accuracy and in the life of the gun. An increase in weight of projectile with a lower muzzle velocity may give better penetration at long ranges, but the loss in danger space must also be considered. An increase in the angle of fall also increases the cross-breaking stresses of the projectile on impact with vertical armor.
(3) By changing the shape of the projectile, a very material increase in range with corresponding increases in flatness of trajectory and in danger space, and finally in striking velocity and penetration, are obtained, especially at long range. By changing the radius of the ogival head from 2 ½ to 7 calibers, the striking velocity has been increased by fully 30 per cent. The value of this change cannot be emphasized too strongly, for it is a gain in the true sense of the word, since it increases the value of a gun 30 per cent without any cost whatever; the charges, the velocity, and the pressure being the same for a long pointed projectile as for a blunt pointed one, the gain being entirely due to the reduction in the resistance of the air to the projectile in flight.
(4) By increasing the initial velocity, the striking energy of the battery can be increased, but in this case as well as that of the increase in weight of the projectile, the gain cannot be obtained without increasing the charge, the maximum pressure, and the erosion, consequently, not without shortening the life of the gun. If, however, the same muzzle energy of the gun is used, the heavier projectile will show better than the lighter, high velocity one, especially at the longer ranges.
The practice of filling A. P. projectiles with high explosives is now universal. The general tendency at the present time is to require projectiles not only to perforate the heaviest armor now existing, but also to carry a large charge of high explosive. If a large projectile has a penetrating power greater than the heaviest armor, it is clear that the capacity of the shell cavity can be increased more than proportionately to the increase of caliber. Thus the larger the caliber, the greater the shell cavity, the heavier the bursting charge, and the greater the efficiency of the projectile.
As before stated, it has been proved by actual firing that the heavier the projectile, the more accurate the shooting; consequently, from the viewpoint of accuracy, penetration, and effectiveness, the caliber of the gun in the primary armament should be as large as possible. Now, the larger the caliber, the heavier the armament; and the greater the space required for its installation on board ship, where these two factors, weight and space, are always limited; consequently, as in most engineering questions a compromise must be made to determine the "smallest big gun" that will fire a projectile that not only penetrates at battle ranges, the heaviest armor afloat, but also carries a sufficient quantity of high explosive to insure the desired effect behind the armor, all this with a reasonable margin of assurance and no more.
The most advantageous composition of battery, as regards the caliber, having been determined, it remains to decide upon the arrangement of the battery, in order to obtain the greatest arc of fire, or maximum fire efficiency from each gun. As the ahead-and-astern fire is necessarily limited and must always be less than the broadside fire, it follows that main engagements will tend to use broadside fire in order to have the maximum number of guns in action; and, as a gun that fires on either broadside is equal to two guns that fire on one side only, the endeavor is to place all, or as many guns as possible, on the center line, due regard being paid to obtaining the greatest height above the water line consistent with maintaining the proper stability of the vessel. Great care is also necessary to avoid "interference" between guns due to the blast effect, etc. Superposed turrets, which increase the number of guns are objectionable, as they are too cramped to furnish proper ammunition supply, and add materially to the height of the enemy's target. It was the recognition of the above principles by American designers, in the plans for the Michigan and Delaware classes of vessels that first led the way to the now accepted designs for vessels of this class. The most conspicuous result of the adoption of the "all big gun" principles has been the intensified competition between naval powers for the possession of the largest and most powerful units, the result being an expansion of dimensions aimed at increasing the actual or proportionate power of the broadside by adding to the number of guns available on the beam. The first vessels built on these principles for Great Britain, Germany, Japan, and the United States, all had eight guns bearing on the broadside, but with differences in the aggregate power required to produce the broadside. The Michigan class obtained it with a total armament of eight big guns, having four twin turrets on the center line. The original dreadnought needed ten guns, having only three turrets on the center line and two abreast on the beams. The German and Japanese had six twin turrets to produce an 8-inch broadside, two turrets on the center line, the other four being placed in pairs abreast. The "beam fire efficiency" of the various types—the relation of broadside to the total armament—was, therefore, 100 per cent for the United States, 80 per cent for the British, and 66.6 per cent for the German and Japanese. The United States design undoubtedly was, and is, the most efficient, and has been consistently followed ever since by its Navy Department. All other powers have come to the center line arrangement for their capital ships, the differences being merely in the number and caliber of guns adopted for the primary armament. The American practice is that the controlling factor in battery arrangement is the number of turrets and not the number of guns, and it is believed that the four 3-gun-turret-arrangement presents the best all around solution of the problem.
To sum up, the general conditions governing the primary armament of the modern capital ship are as follows:
- The greatest weight that can be allowed to the armament.
- The number of gnus required.
- Their disposition within each turret (twin, triple, quadruple).
- The disposition of the turrets (superposed, etc.) affecting the weight of armor carried.
- The weight and number of rounds of ammunition carried. It is evident that for similar types of guns and turrets, the larger the caliber of the gun, the larger will be the turret and the greater the ammunition weights; and although modern design has done something to reduce the ratio it is still very large.
In one respect, the theoretically perfect arrangement of guns of a fleet would be to have them mounted in single turrets widely separated. Then damage to one gun would not put another good one out of action, but to do this would necessitate a ship of enormous size, and other vital characteristics would have to be surrendered. Economy of space could not be obtained in a single gun turret and all machinery and other mechanical equipment necessary for the control and service of the battery would be required in complete sets for each gun; whereas, in the case of more than one gun in a turret, a certain part of this mechanical equipment can serve all guns in the turret. Upon the other hand the theoretically perfect arrangement for director firing would be to have all guns on a ship in one turret in one mounting. With one ship engaged such an arrangement would invite defeat owing to the chance of all guns being put out of action by one shot. But if several such ships were engaged the effect on the outcome of the engagement is reduced as the number of ships engaged (within reasonable limits) is increased.
In general, the developments in turret design have progressed from the use of a single gun in a turret, to a maximum of four guns in a turret. It may be accepted that this development is based upon sound principles and follows a corresponding increase in the size of the navies of the principal powers. The primary objects to be accomplished in the design of a turret are accuracy and rapidity of gun fire, and efficiency and reliability of all mechanical features of the turret, combined with the maximum possible protection against damage by the enemy's gun fire. The details of gun and mount should be worked out to eliminate excessive dispersion, and to avoid any increase in dispersion, caused by any progressive, permanent deflection in metal which is placed in stress, by the forces resulting from the discharge of the guns. The various machines installed for use in the service of the guns should be designed with a liberal factor of safety to insure continuous operation, over an extended period of time, and should be simple in design to facilitate upkeep, and to avoid the necessity of too much mechanical skill and experience on the part of the personnel. Protection is similar to insurance against accident and should be the maximum which can be obtained without undue sacrifice of accuracy of gun fire and mechanical reliability.
In the consideration of alternate turret designs it is accepted that all of the best conditions cannot be found in one design but that the design chosen must be superior in most of the important requirements.
The most important subjects that require consideration in connection with turret designs are:
- Accuracy of lire.
- Rapidity of fire.
- Simplicity and reliability of operating machinery.
- Strength and reliability of turret structure.
- Size of barbettes and dead weight of turrets.
- Protection of gun, mounting, and personnel.
From the constructor's point of view it has been practically demonstrated that the weight of installation per gun is the least for a 3-gun turret, and increases in both directions from this number, due to the fact that the space occupied by that portion of the three guns contained inside the turret pan, is bounded very nearly by a square, which is the largest rectangle which can be inscribed in a circle. It is also true that the least weight is required for designs where all guns are carried in one slide as one supporting and one elevating system is sufficient for all.
From an Ordnance point of view the size and weight of turrets are not of great importance. Extra weight is conducive to rigidity, and consequently accuracy and consistency in the performance of the gun, while the size of the turret affects the target area presented to the enemy, but from the point of view of ship construction they both materially affect the design of the ship, and must be kept within reasonable bounds.
As stated above, the greater the number of gun emplacements, the greater the difficulty of putting all guns out of action. Recent designs have varied between two and six emplacements per ship, and ideas recently seem to fix upon four as a happy mean between the two extremes. Two turrets forward and two turrets aft permit a most satisfactory design of the ship as a whole, and should be sufficient when it is considered that the total number of emplacements involved in the action is equal to four times the number of ships engaged. It also provides the ideal arrangement for fire control purposes, such as divided fire, etc. The abandonment of the 6-turret ship for one with four turrets naturally brought up the question of placing more guns in a turret to make up the same total number of guns; and it is believed that the practicability of this alternative, coupled with the economy of turret weights per gun, constituted the principal arguments in favor of the latest design of battleships carrying four turrets with three guns in each.
Another factor was introduced at the same time, however, which also materially affects the problem; namely, the size of gun used. This increase involves the following:
Greater damage done by one hit obtained at a cost of:
Greater turret weights per gun.
Greater size of turret,
More powerful operating machinery,
Greater ammunition weights to be handled and stowed, and
Greater cost.
All provided a reduction in the number of guns is not made.
From the 12-inch to the 14-inch no radical changes were made in the methods of handling ammunition and serving the guns, consequently the character of turret machinery was generally the same, but of an increased capacity in the larger turrets. In stepping up to the 16-inch, however, the proper handling of the heavy ammunition weights involved a certain change in type as well as power of machinery, which in general resulted in more space being required for such machinery. In following the old rule that the turret pan should be only large enough to accommodate the guns in recoil position, the proportionately greater space required by the other turret gear resulted in a more crowded turret, with less space left for the crew. Operating space was thus sacrificed to obtain a gun of greater caliber, without either reducing the number of guns, or materially increasing the size and weight of turrets.
In commenting upon the details of turret designs as they stand to date, the following points are made for comparison between the triple slide and the separate slide mountings:
(1) Accuracy of Fire.—In the tests and target practices so far held there is nothing to show conclusively that the accuracy of guns individually mounted is any greater or less than that of guns mounted in one slide. It may therefore be assumed that about the same accuracy of hitting, as far as present data and experience show, can be obtained by either type of mounting, as it also appears that either type permits of sufficient rapidity of fire to meet battle conditions. However, any change in gun alignment due to settling of turret structure can be corrected in the single slide mounting and not in the triple slide.
(2) Simplicity and Reliability of Machinery.—With the separate mounting, each gun elevates individually, unless the elevating system is cross connected. Three complete elevating sets are required and these three sets must be interconnected by a system of clutches, gears, valves, etc., which requires considerable care and knowledge on the part of the personnel properly to operate it. The system when interconnected also depends for accuracy upon that of the triangle established by the centers of gun trunnions, centers of trunnions to oscillating bearing, and centers of connection of elevating screws to the slides, as well as on the accuracy of the .screw thread cut on the elevating screws. With this system, the adjustment of the three guns in the same horizontal plane can be effected; and, if the machine work on the various parts, as well as the work of installation, is accurate, then the three guns will elevate and depress parallel to each other; until damage to the system, due either to internal causes or enemy shell fire, introduces an error in the relative position of trunnion centers, oscillating bearing centers, or other parts of the system. This gives the maximum of flexibility to the system and enables one gun to be kept in operation after the failure of its own elevating gear. In the triple slide type of mount, the ability to elevate each gun separately is sacrificed to obtain accuracy of elevation for the three guns which must move through the same vertical angle at all times under the control of one elevating screw. Any derangement of this elevating system, therefore, affects all three guns alike. On the other hand, since the oscillating weights are tripled, the elevating motors must be greatly increased in size to maintain the same rapidity of movement and handle any unbalanced forces due to blowing off a muzzle, etc. With independent slides, the damaged gun may be cut out.
With guns separately mounted, it is necessary to provide a sight for each one and the only practicable location for these sights is underneath the guns, unless the distance between guns is materially increased in order that room may be provided for a pointer's station between the guns. Such an increase in distance between guns would amount to at least 6 feet total and would necessitate a corresponding increase in the size of the turret. The guns at the high elevations now required (40°) interfere with the sight setter and pointer, and the movement of the telescope eye-piece is so great that the pointer is materially handicapped in his work of laying the gun for pointer fire, unless movable pointers' seats are installed. Alternative control stations are very desirable to cover cases where minor casualties place the stations in operation out of action. Three independent stations require accurate adjustment of the sighting appliances of each, but once adjusted give additional insurance. For director fire it is not necessary to have the guns cross-connected, and each gun can be independently laid not only more accurately but faster, as the motor is only handling the load of accelerating one gun, and it is believed the guns should be normally handled this way. In the case of the latest triple slide design, the work of adjusting guns with sights is simplified as the adjustment consists in aligning two sights attached to the same slide with the guns therein. It is desirable to provide, as far as possible, auxiliary means for accomplishing all the various functions involved in the service of the guns, but in the case of guns independently mounted, this can only be obtained in many cases by the installation of duplicate equipment for each gun, or, as is the case with the elevating gear, by the introduction of a cross-connecting system in order to make use of any, or all, of the three electric motors in elevating the guns, and this cross-connecting system requires considerable space in the turret for its installation.
On the other hand, the separate installations permit of correcting each gun's angle of elevation for erosion and should thus materially reduce the pattern.
The design of machinery for the three guns must be a compromise in order to secure the third gun; this has already been pointed out in the case of sights, and exists also in the case of elevating gear, which, in general, must be arranged in line with the gun and underneath it, rather than in an athwartship plane; and also in the case of shell and powder hoists where interference is experienced either with the right or left gun depending upon whether the hoists for the center gun are constructed right or left handed. Another important influence on the weight of the total gun mounting is the extent to which the alternative systems of power and hand working are employed. Furthermore, the question of perfect balance means increased weight over a design where these considerations are not weighed too carefully.
The ammunition handling machinery must be capable of rapid movement, and the methods of bringing ammunition from the hoists into the guns must be simple and expeditious, and necessitate only the minimum of fatigue to the crew, while maintaining a continuous supply over a protracted period. These requirements in design involve the question of the choice between hydraulic and electric prime movers. Reliability is the first consideration. It is essential to obviate any chance of derangements by shock or direct impact, and, as far as possible, from the shattering effect of high explosive shell bursting in the vicinity of turret gear and machinery.
(3) Size of Barbette and Dead Weight of Turrets.—Other things being equal, the size of barbettes for guns separately mounted must necessarily be greater than that for guns mounted in one triple slide for the simple reason that distance between gun centers must be greater to provide space for the inner trunnions. This involves a greater target to be presented to the enemy's fire, or, if the same size barbette is used in both cases, then the turret carrying the three guns in one slide will be a more roomy turret.
Size of barbette and weight of turret go hand in hand and any appreciable reduction in size, when it is realized that a 16-inch 3-gun-turret complete weighs approximately 2000 tons, means a reduction in weight which materially assists the naval constructor in producing a better design of ship. It is believed to be very difficult to design a turret structure for a triple slide which will be as rigid as the structure for a turret mounting single slides, also the distribution of the load on the turret roller path is more satisfactorily provided for in the case of independent slides and the turret pan can be more substantially braced and tied.
If sufficient diameter of barbette is selected, shell and powder hoists can be provided for each gun in both types of turrets, but in the case of the triple slide design the advantage obtained by a smaller barbette must be given up.
(4) Distance between Guns.—Various turret designs in the past have involved various distances between centers of guns. On the first tests of the triple slide arrangement it appeared that the accuracy of flight of the projectiles was possibly impaired by interference between shells in flight. This interference appeared to be a serious defect, and considerable experimentation was conducted using delay action coils to produce successive firing of the three guns. Tests of the mount using these coils at the proving ground indicated that an improvement in dispersion was effected. Later on, in service, this delayed action idea was apparently overdone; and inaccuracies developed due to the fact that the guns were mounted on a movable platform, and fired generally on the middle of the roll, at which time the angular movement of the ship was at its maximum. Also, experimental firings showed that the variations in ignition and inflammation of the powder were much greater than those introduced by the delay coils. This resulted in the abandonment of the delay action coil, with the result that smaller dispersion was obtained. Greater separation of the guns in addition to giving less blast interference provides a stronger front plate for the turret in the single slide design, and this feature is well worth considering.
It is believed that imperfections in the design of projectiles, variations in the amount of recoil of the gun at the instant the projectile leaves the muzzle, and the question of rigidity of the mount have more effect upon the dispersion than the distance between guns. In a special firing of a 3-gun turret, when the wing guns only were fired, the patterns were substantially the same as those from a regular 2-gun turret.
(5) Safety Features.—It is evident that separating bulkheads cannot be installed in the turret utilizing the triple slide. This may be considered a loss of protection from the enemy's gun fire. On the other hand, the advantage obtained shows up in the greater facility of control of the personnel as all are in one compartment.
As far as known, foreign navies do not use separating bulkheads, which goes to show that there is not universal agreement as to their necessity. They take up a certain amount of valuable space in the turret, which tends to increase the congestion already existing. They are not entirely flame proof under all conditions, as openings must be provided for access and transfer of ammunition in case of breakdown, where one gun has to be served from the hoists of another. These disadvantages are incurred for the advantage of additional safety and also to meet the requirements of all the Departmental Turret Board reports, and to prevent demoralization of personnel in action, which is believed to be a necessity for service of guns in battle. A great advantage from a structural point of view is also obtained in the case of the separate slide design by the fact that the roof of the turret can be well supported. This increases the protective efficiency of this type of turret, as the roof derives considerable support from the bulkheads and stanchions which can be installed.
In the case of a hit on the turret front plate, the port clearances are necessarily so small that a fragment might easily jam the single slide. One possible advantage to the triple slide type might be derived from having the sight line come out through the side plate of the turret, whereas in the case of the guns separately mounted the sighting arrangements are provided through the lower part of the gun port. This is a doubtful advantage, however, as movement of the front plate would probably entail a certain displacement of the side plating with the result that the trunnion types of sight might well be placed out of action. When the question of .sealing the gun ports to keep out water and protect the lenses of sights from spray is considered, the trunnion type of sight on the triple slide possesses considerable advantage over the other arrangement. In the case of a rammer jamming in a gun, it is evident that the separate slide type of mounting is superior, since the fire of the other guns would not be affected unless the elevating gear is cross-connected, in which case the clutches and other devices for cross connection would have to be thrown to operate the guns individually.
The reasons leading to the adoption of the separate slide may be summarized as follows:
It is self-evident that the chances of victory in battle lie with that side whose armor and armament is so disposed as to enable it to inflict the maximum damage upon its adversary, and, at the same time, minimize the damage it receives itself. This broad principal demands that each gun shall be so mounted as to enable it to deliver throughout the battle, the most rapid, accurate and uninterrupted fire possible; moreover, it further demands that the armor protection be so disposed as to reduce the effects of hostile hits to a minimum and to restrict such damage as may l)e unavoidable to the immediate vicinity of the hostile hit. It is evident that to mount guns in such a manner that the rapidity, accuracy, or duration of fire of one gun is in any way dependent upon the operation or condition of adjacent guns is a violation of this fundamental principle that cannot be justified upon grounds of simplicity, compactness or target practice results.
It is not difficult to imagine many ways in which one well-placed hit could totally disable a single slide turret, nor is it difficult to imagine many casualties of a minor nature, in themselves, that would more or less seriously affect the volume of fire. The fire of three guns is entirely dependent upon one elevating screw and its accessory mechanisms. The jamming of one gun, even by a shell fragment lodged in a port opening, interrupts the fire of all three guns; the failure of one gun to return to battery, or a jammed rammer will cause a similar interruption of the fiber of all three guns. With the three guns mounted in separate slides, a minor casualty will affect the fire of only one gun and it is difficult to imagine a hit so well placed as to disable more than one or possibly two guns.
The curve of total trunnion pressures for a three-gun turret, using guns from 12-inch to 18-inch caliber, takes the form of a hyperbola which has a considerable shoot upward beyond the point corresponding to a caliber of 16-inch. This shows that the advantage gained begins to drop off rapidly beyond this point, since the necessary strength required to hold the gun in the ship involves a corresponding rapid increase in size and weight of turret. Also, the handling appliances for the ammunition increase rapidly in size, and capacity, thus requiring more space for their installation and further decreasing the relative advantage obtained in mounting three guns in a turret.
The above discussion points most forcibly to the great necessity of simplicity and ruggedness in turret designs. The mental and moral strain of battle reduces the ability of the personnel much more, (when cool headedness and careful training in the intricacies of turret machinery are required) , than is the case when simple duties are to be performed which do not require care, knowledge and good judgment on their part. At best, turret machinery must be more or less complicated" to perform the various services required. In its simplest form it will tax the brains of the average man, and if he is taxed beyond his capacity, then disaster is sure to follow.
The preceding discussion shows the conflicting requirements to be met in turret design, and the ever-present conflict between operational simplicity and numerous demands for alternative systems, the resulting plans being as usual the best possible compromise after assigning the proper weight to all the various factors considered.