MILITARY CHARACTERISTICS AND ORDNANCE DESIGN
By Commander H.F. Leary, U.S. Navy
1. The General Board having prescribed in general terms the military characteristics of a ship, such as type, speed, radius of action, armament, armor protection, etc., for any type of new construction, the various technical bureaus, upon approval, and under the direction of the Secretary of the Navy, proceed with the development of the plans. Preliminary or basic designs of the vessel are prepared by the design section of the Bureau of Construction and Repair, and the various other technical bureaus are requested by that bureau to furnish data regarding features of design under their cognizance for incorporation in these designs. The Bureau of Ordnance is requested to furnish preliminary designs or type general arrangements of ordnance equipment, together with weights and centers of gravity of all ordnance material to be carried by the vessel, and to submit general recommendations regarding armor protection. In order that this information may be available and be furnished without delay, it is necessary that the trend of ordnance design be anticipated to a great extent by the bureau.
2. The preparation of designs for turret, secondary battery, or anti-aircraft mounts, torpedo tubes, etc., are undertakings requiring six months to a year's time. The information required by the Bureau of Construction and Repair is generally furnished within a week or two after the request is made, and the design must be sufficiently worked out in advance to furnish at least reliable preliminary data regarding weights and dimensions. Ordnance design is constantly undergoing a process of evolution and systematic development, due to increase in caliber and power of guns, to the development of new weapons and instruments of warfare, and to the constant efforts of nations to produce types of vessels possessing offensive and defensive features superior to those developed by others.
3. Generally, work of basic design is done by several experienced men in such a manner as to cover the requisite features with accuracy, with the least detail possible and with the least expenditure of time. The governing idea is the determination of the important features of the vessel, after weighing all the possibilities and their various relationships, both to the design itself and to each other. Once this is accomplished satisfactorily, the necessary sketches made, and the data tabulated, the work of developing more detailed plans may be at once undertaken with efficiency and assurance. Aside from the element of loss of time and money due to unfortunate selection of characteristics proposed, the main advantage to be anticipated from the organization of a basic design section is the facility with which it is possible to investigate the effect of variations in dimensions, power, capacity, etc., without occupying the time of the regular drafting force or being embarrassed by relatively unimportant detail. The value of such a section was first formally recognized in the Bureau of Ordnance during the war, and since then all departmental designs have been handled by it, and the results have been such as to establish this system firmly. The caliber of main battery guns of battleships of the leading nations has increased 50 per cent during the past ten years, and in the same period of time the submarine and the flying machine have been perfected; and, by their advent, warfare has been extended into the air and below the surface of the sea.
4. To be prepared to meet the demands of the General Board and the Bureau of Construction and Repair, and to keep up with the progress of ordnance development referred to, it is necessary that improved types of ordnance design be under constant investigation by the Bureau of Ordnance. The main subjects to be investigated and covered by this bureau in connection with the design of capital ships are the questions of caliber of main battery guns and armor protection, both of which are largely dependent upon the assumptions made as to the probable future battle range.
5. Assume, for instance, that we have reason to expect a large increase in battle range, due to improved methods of fire control and increased accuracy of guns. In such a case a complete study and estimate of the situation is undertaken by the Bureau of Ordnance. Let us suppose, as a result of this estimate, that it is decided to investigate the use of the 18" gun for future capital ship construction. Orders are issued by the Chief of Bureau of Ordnance to the design section to proceed with the design and preparation of the necessary preliminary drawings for the gun, projectile, turret, and other features making up a complete unit. The first step undertaken is the preparation of a preliminary design of gun. The weight of the projectile is tentatively decided upon in order that the ordnance engineer in charge of gun design may have a starting point from which to work. A careful survey is made of the problem to determine the muzzle velocity required to give the desired penetration at the battle range under consideration. Weight of projectile and muzzle velocity being determined, consideration is next given to the problem of interior ballistics. From records of past gun performances and other information available; a powder is selected that will give the desired velocity to the projectile without exceeding normal chamber pressures and give the greatest number of foot pounds of work from each pound of powder in a gun of 45 to 55 calibers in length. For obvious reasons, it is desirable to use existing powders. When this is not possible, the powder expert at the Naval Proving Ground is consulted and a new powder is tentatively selected, of such web thickness as to give the desired rate of burning.
6. The principal characteristics of the gun having been determined, the next step is to prepare a general arrangement drawing. This drawing shows the powder pressure curve, velocity of projectile curve and the strength curve, together with assigned shrinkages and all necessary dimensions. No effort is made at this stage to prepare detail drawings. These, together with all other manufacturing drawings, are prepared by the Naval Gun Factory from the general arrangement drawings furnished by the bureau, when orders are issued to proceed with manufacture.
7. As soon as a decision is reached regarding the weight of the projectile, this data is turned over to the engineer in charge of projectile design, and this work proceeds simultaneously with the gun design. Until very recently, little was known regarding the important principles entering into projectile design. Projectiles were designed that were strong enough to stand the heavy pressures in the gun without breaking up and which gave satisfactory results from the standpoint of armor penetration. Little was attempted, however, in the design to produce a projectile which would give the most satisfactory results as regards dispersion. From what has been developed during the past two years, it has been found that by observing certain principles of design that are concerned principally with obtaining the proper relation between rotation, moment of inertia of the projectile about the longitudinal and transverse axis, combined with proper band design, the dispersion may be greatly reduced below that obtained in the past when these features were not carefully considered.
8. The features of gun and projectile design having been determined, it is customary to proceed with the manufacture of a type gun and slide, in order not only to prove the important features of gun and mount design but to initiate experiments at the Proving Ground dealing with powder, armor penetration, and accurate ballistic data. Use is also frequently made of wooden models of turrets, guns, and mounts built full size at the Naval Gun Factory.
9. Upon completion of the preliminary plans of the gun, and without waiting for the completion of the type projectile, gun, and mount, the design section of the bureau is engaged in the preparation of the preliminary plans of the turret. It is the present rule to mount turret guns so that practically the maximum range of the gun can be obtained. For all practicable purposes, this means 40 degrees elevation, and the turret is designed on this basis. The turret design is first blocked out roughly in order to get an approximate idea of the best arrangement of mount, ammunition hoist, handling rooms, etc. It is essential that the dimensions of the turret, including the barbette, be made as small as possible, not only on account of the saving resulting in armor weights, but also on account of the reduction of target exposed to the enemy. The diameter of the barbette is governed by the distance from the center of rotation to the extreme position of the gun in recoil. This distance is therefore kept as small as practicable by moving the center of the trunnions as close as possible to the turret front plate, by reducing the distance from the center of the trunnions to the breech of the gun to the minimum amount, and by limiting recoil of the gun. By moving the center of trunnions close to the front plate, we are also able to reduce the port opening through the front plate to the minimum size. The distance from the center of the trunnions to the breech of the gun is kept a minimum by increasing the weight of the gun yoke above what is actually needed to withstand the forces of recoil or to act as a counter-balance. It has been found from past experience that the trunnion pressure will not be excessive if the recoil of the gun is limited to about three calibers in length. With the position of the gun in the turret approximately determined, it is possible to fix the diameter of the barbette and the exterior dimensions of the turret armor. After the determination of these dimensions in the manner indicated, the elevating gear, rammer, powder and shell hoist machinery are laid out to go in the space provided. Arrangements are also made for the accommodation of personnel, fire control instruments, and range finders.
10. As the design is being laid down, computations are made to properly balance the various parts about the axis of rotation. All oscillating weights are balanced about the trunnions and, as far as practicable, the revolving weights are balanced about the vertical axis of the turret. After the upper portion of the turret has been sufficiently developed, consideration is given to the question of ammunition supply. The best methods for storing and handling the projectiles and powder charges are agreed upon, and machinery is developed to supply projectiles and powder to the gun at the maximum rate, at least three rounds per minute.
11. In the design of powder hoists, it is considered important that the supply of powder from the magazines to the guns be conducted with the least liability of danger to personnel and safety of the ship from explosions that may occur in various parts of the turret. To accomplish this, flame-proof doors are provided In all handling rooms, and the hoist is designed with interlocks, arranged in such a way that there is no direct communication between the turret chamber and magazines at any time. In order to localize the damage resulting from premature explosions and other causes, it is the practice to provide divisional bulkheads between individual guns, and to enclose the turret officer and fire control group in a booth at the rear of the turret.
12. With preliminary plans available, the Bureau of Ordnance is prepared to supply the Bureau of Construction and Repair and the General Board, within a few days, with such information as is required to develop the preliminary plans of the vessel. In case information is requested regarding plans of a type of construction which has not been anticipated by the Bureau of Ordnance, the development work proceeds in a manner similar to that described above, but it is not possible in such a case to prepare plans in the same amount of detail. As an illustration of what may be accomplished in an emergency, the recent preliminary plans for the 6" twin mounts for scout cruisers were prepared, and complete information regarding weights, cost, etc., furnished within a period of three weeks. This mount represented an entirely new departure in 6" mounting, but owing to the close co-operation existing between the Bureaus of Construction and Repair and Ordnance it was possible to furnish complete information regarding the mount, and necessary modifications to the ship plans, so that a decision was reached by the General Board and recommendations made to the Secretary of the Navy regarding manufacture within the short period of time mentioned.
13. The Bureau of Ordnance has a series of standard ordnance allowances of ammunition, spare parts, tools, accessories, etc., and the caliber and type of guns having been once established, the use of these tables permits the Bureau of Ordnance to supply the Bureau of Construction and Repair with a table of estimated weights and centers of gravity for all ordnance material entering into the design. Tables are also furnished the Bureau of Construction and Repair, giving the working circles required for all guns, the trunnion pressures which the ship's structure must withstand for each type of gun, and blast diagrams showing effect of muzzle pressures at various distances. This gives all the data necessary to work up contract plans.
14. The General Board is provided with tables and formulas which give all the data necessary to determine penetration of armor, the data being sufficiently broad to cover any combination of caliber of gun and thickness of armor.
15. While the General Board is discussing the tentative designs, representatives of the technical bureaus are called before it, and a general discussion of the various characteristics ensues in which armor is considered as well as other characteristics. The General Board then draws up tentative characteristics and sends them to the Bureau of Construction and Repair, where the various sketches necessary to show the general details of the design are worked up.
16. From these general sketches, which may cover a number of variations in design, the various weights of armor are computed by the Bureau of Construction and Repair, and then the drawings and weight data are turned over to the Bureau of Ordnance for detailed study. This study is based on general principles of protection only. If the records of the Proving Ground cover experiments which parallel the conditions laid down in the design, the bureau can determine with reasonable accuracy the protection which the various designs afford. If the ship possesses any unusual features, it is probable that no experimental data will exist covering parallel cases, and in this contingency it will probably be necessary to undertake a certain amount of experimental firing at the Proving Ground.
17. When the Bureau of Ordnance has completed its preliminary analysis of the design, or designs, a report is submitted to the General Board, through the navy department, which points out how closely the proposals meet the requirements, or points out where modifications or changes in the proposed designs may be made with benefit to the protection. Up to this stage the quantity of armor allotted to the ship or, in other words, the percentage of weight which can be devoted to armor protection, has been more or less approximate, and if the research of the Bureau of Ordnance shows any unusual conditions, it may be necessary that the allocation of armor be changed. For instance, it may be that a proposal will be made to change the arrangement or armor in such a way as to lighten the total quantity of armor required, or it may be that the research will show that the protection afforded Is entirely inadequate and it may be necessary to request an addition to the allocation of weight for armor.
18. Upon these preliminary researches, the General Board generally bases the final general characteristics of the vessel, and these final characteristics are again transmitted to the Bureau of Construction and Repair for the preparation of final plans.
19. These final plans are again referred to the technical bureaus, and the armor plans are then gone over with the idea of investigating them to determine with precision, not only the amount of protection afforded, but the details of construction, size of plates, connection between plates and bulkheads, etc. It is generally the custom of the Bureau of Ordnance to lay these plans before the manufacturers of armor, in order that the details of plate size, etc., may be agreed upon.
20. After this work had been concluded, and the General Board has given final approval to the plans, the Bureau of Construction and Repair draws up contract plans, which are again referred to the technical bureaus. These contract plans are then transmitted to the armor manufacturers for detailed comment, and final fixing of joints, gauges, size of plates, etc.
21. In general, the cognizance of the Bureau of Construction and Repair and the Bureau of Ordnance in regard to the armor is as follows: the Bureau of Ordnance is, in general, responsible for the quality of armor and its manufacture in conformity with the contract plans.
22. The Bureau of Construction and Repair is, in general, responsible for the means of attaching the plates to the ship, connecting the plates to each other, etc. The two bureaus work together jointly in insuring that the plates are made as large as possible (to eliminate joints), and that they are secured to the ship and to each other with the greatest security possible, consistent with the capabilities of the armor manufacturers. Similarly, the Bureau of Ordnance is responsible for fixing the manufacturing tolerances and dimensions to meet the demands of the ship builders as expressed by the Bureau of Construction and Repair.
23. Prior to the advent of what may be styled modem construction, various arrangements and thicknesses of armor were tried, use being made of the obliquity of impact. Gradually design settled down to vertical belts, with few variations, the Kahtadin being the only ship which departed from this principle. From 1887 to 1903, armor was gradually increasing its ascendancy over the projectile. It was during this period' that modern naval construction ideas were really developed. During this period the torpedo had an insignificant range and the ram was frankly considered. Gradually, the power of guns was increased, the range of torpedoes was increased, and ram discarded and the generally accepted battle range was increased. After about 1903, however, the development of the projectile and the further increase in gun power gradually reduced the ascendancy of armor. This evolution has proceeded to the present day, but until about 1917, architecture never varied.
24. During the past few years there have been two distinct developments in naval architecture which affect armor: It is now conceded that torpedo risks may be incurred, and this development in opinion has been coincident with a very important and efficient development of anti-torpedo and anti-mine protection. Whether the change in opinion resulted from the development of under-water protection, or whether it was independent of it, is a question, but it is evident that in the present state of opinion and under-water protection, greater risks of torpedo damage will be taken. If this is correct, we are again forced to the conclusion that a material increase in the relative efficiency of our armor protection is mandatory. The other development in architecture is the inclination of the side armor outboard, which was first (recently) used on the British battle cruiser Hood, and later copied on our battle cruisers. These are the first instances of a departure from that system of architecture which had been followed so consistently for about twenty-five or thirty years. It is true that in our battle cruisers the inclination was used to bolster a markedly small plate thickness, and in the Hood it was used to cover a reduction in thickness of the belt to 11 inches from 13 inches in the Queen Elizabeth. However taken, it is a break in the long train of similar ships.
25. Before armor can be properly distributed, it is necessary to know:
(a) The chances of hitting various parts of the ship.
(b) The kind of projectiles the armor must resist.
(c) The effect of such projectiles on armor in various arrangements.
When considering armor, the thickness and quantity are, of course, limited by weight. Taking this limiting weight, we must properly balance the protection given various parts of the ship working on the principle of "all or none," that is, vital parts should be fully protected, but very valuable weight should not be lost by the distribution of light armor around unimportant parts of the ship. At a very short range the side armor receives more hits, but at medium and long ranges more hits are recorded in the deck armor than in the side armor. At modern battle ranges only about 25 per cent, or less, of all hits will be received in the side armor and the target is essentially a horizontal one. Side armor must be thicker than deck armor, not because it is more likely to be hit or covers more vital parts—but because at short range when velocity is high it is subjected to more direct impact. Side armor may be hit at normal impact, but deck armor will probably be hit at an angle of more than 45 degrees from the normal. It would be useless to provide very heavy side armor and very thin deck armor, or very heavy deck armor and very thin side armor just below the water-line, where direct hits may be received.
26. In regard to attack by bombs from aircraft, there seems little to be feared in the way of penetration. A bomb simply dropped obtains a disappointingly small velocity even when dropped from so great a height as to make its aim uncertain. Even when dropped from extreme heights, bombs will reach a certain velocity at which the acceleration, due to gravity, is equaled by the retardation due to air resistance. This is called the "terminal velocity," and a study of it shows it to be small. To actually drop a bomb with the hope of its weight carrying it through the protective deck is practically impossible. It would take an altitude of about 10,000 feet to put an armor-piercing bomb through a 3 ½" deck.
27. The next question is that of armament; here we are, as always, limited by weight and space, and several factors must be considered. Our doctrine should be the maximum number of the lightest and handiest guns which will, at extreme fighting range, successfully penetrate the heaviest armor with which enemy craft will oppose them. The factors governing the decision as to the type of primary armament as regards its caliber are:
(a) Range
(b) Penetration
(c) Explosive effect
(d) Probability of hitting
(e) Rapidity of fire.
The total weight allowance will fix the number of guns and as between different calibers the factors which most influence decisions are (b) and (d), as the differences between the others are small. The Naval Treaty on Limitation of Armaments has fixed the caliber at 16", and it thus becomes a race between designers as to who can turn out the most powerful gun of the lightest weight, the two variables being muzzle velocity and weight of projectile.
28. The most advantageous composition of battery as regards the caliber for the primary armament having been determined, it remains to decide upon the arrangement of battery in order to obtain the greatest arc of fire, or maximum fire efficiency, from each gun. The American practice has been standardized, and it is believed that the four 3-gun turret arrangement of the Pennsylvania presents the best solution of the problem.
29. 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 for the armament.
- The number of guns required,
- Their disposition within each turret (twin, triple or quadruple).
- Disposition of turrets (superposed, echelon, etc., as affecting the weight of armor carried).
- The weight of the projectile and powder charge as affecting the number of rounds of ammunition to be carried per gun.
30. It is evident that for similar types of guns and turrets, the larger the caliber of the gun, the larger the turret, and the greater the ammunition weights, and, although modern design has done something to reduce the ratio, it is still very large.
31. The main battery does not fulfill all the necessary functions required of the complete ship's battery, and it is necessary to place on board ship additional weapons which are in the nature of a protective armament to fulfill special requirements. The primary mission of a battleship has already been cared for by the installation of the heavy armament which is given priority throughout. Therefore, when we come to this secondary armament we find that the greater part of the allowable weight has been used up and that the best spaces and locations for guns have also been assigned. Consequently, the secondary armament is limited to the smallest calibers, the lightest weights, and the smallest number of units that can be expected to do the required work acceptably. The arrangements for these secondary batteries are influenced all the way through by the priority given the main battery, by the necessity for limiting the size and number of guns, and by the necessity of avoiding blast interferences. Ships are crowded more and more by the demands for a heavier main battery, more armor protection, and more speed and greater steaming radius. It is believed that for future construction the secondary battery will probably be mounted in blast-proof enclosed mounts closely resembling a small turret. This appears to be the best compromise solution that can be obtained. Anti-aircraft guns—at least eight—will be on the upper deck so located as to give the best possible arcs of fire, and will also be used as star-shell battery.
32. In developing the detailed plans, the following points require constant and close co-operation between the Bureau of Ordnance and the Bureau of Construction and Repair:
Ammunition stowage and handling arrangements—safety features.
Torpedo stowage and handling arrangements.
Arrangement of tops and conning towers for most efficient locations for fire control instruments (clear vision, etc.).
Arrangements for mine stowage and mine tracks.
Ammunition hoists and torpedo tubes on submarines.
Also co-operation with the Bureau of Engineering regarding:
Wiring and arrangement of instruments for plotting rooms, torpedo tracking rooms, and all fire control and torpedo control stations. Generally, all voice tube and telephone leads and outlets.
33. It is desired to point out, in connection with this discussion, the very close relation between technical ordnance and gunnery ideas and ship construction ideas, as regards design of ships. Even such a matter as the construction of the enemy's fuses has a tremendous effect. We do not fire at ships merely to penetrate side armor or to disable personnel, but to accomplish their destruction. The protective deck is at present the most interesting target, and we cannot build our protective decks without a clear idea of what the enemy's fuse is capable of. It is believed that it has not generally been appreciated how necessary it is for the three material bureaus (ordnance, engineering, and construction and repair) to co-operate with each other in ship design.