“An examination of facts is the foundation of science.”
A well designed war-ship may be termed an aggregation of compromises. The augmentation or extension of any quality beyond a certain limit can only be made at the expense and by the curtailment of some other requisite, equally, or perhaps more, desirable.
Everything has weight, and to carry weight requires displacement, which involves increased resistance and greater engine power. The distribution of weights so as to produce the best general results is a problem of the greatest importance, for upon it depends the success or failure of the vessel, as measured by the standard of comparison with others.
The cardinal requisites of a war-ship, mentioned in the order of their importance, are:
1st. Defensive power—ability to keep the ship afloat, and the crew alive.
2d. Offensive power—ability to destroy or disable an enemy's ships and men.
3d. Mobility—power to chase down or ram an enemy.
4th. Quarters—giving healthful and sanitary accommodations to officers and men, necessarily conducive to proper morale and discipline.
Of these prime requisites, defence of the water-line is, to a war-ship, a matter of paramount importance; for even though a vessel had the speed of the wind, was armed with the most powerful guns, commanded by the most capable officers, and manned by the bravest crew, all would avail nothing if she could not be kept afloat in combat.
The great improvements attained in the rapidity of manipulation, accuracy of fire and range of the modern breech-loading rifle guns, make the defence of the water-line a matter for the most serious consideration. Percussion shells of large size, each one of which is in itself a mine, will render an efficient defence of the water-line a problem very difficult of solution. But even if absolute protection cannot be attained, the importance of the matter demands the adoption of every available expedient that may lessen the chances of fatal disaster and ensure the flotation of the ship—1st, by keeping the water out, as far as possible; 2d, by freeing the vessel of water, should it unfortunately gain entrance.
A water-line defence, consisting of armor disposed vertically, is at the mercy of elongated shot, concentrating their energy on the small area of their cross sections; and if such armor extends the length of the vessel, the bow and stern are encumbered with a weight entirely disproportioned to its flotative power.
Vertical side armor does not give an efficient protection, unless supplemented by deck-plating; but if the aggregate weight of the vertical armor and deck-plating is distributed over the vessel in the form of a curved shield, having a cross section conforming to the arc of a circle, extending across from side to side, and so placed within the ship as to have its crown slightly above the water-line, with the sides attached to the vessel some four feet below it at ordinary load draught, a much greater measure of protection can thereby be obtained with the same weight of armor; as elongated shot strike it upon their sides, thereby presenting the much greater area of their longitudinal sections, by which they would be deprived of much of their penetrating power. Moreover, the glancing effect of a curved shield will enable a comparatively light plate to throw off a heavy shot.
The zone of danger is the side of the vessel, alternately acted on by wind or water as the ship rolls. It is proposed to protect this vital part by interior deflecting armor; the position of the shield in relation to the water-line to be adjusted by the admission of water to the double bottom.
In combats between ships at ordinary fighting range, horizontal fire is all that need be considered; a vertical target can easily be struck, while it is almost impossible for a projectile fired from a vessel rolling at sea to strike a horizontal surface. Under such circumstances it would be very difficult to land a shot upon the area of a hundred acre farm, to say nothing of the much smaller surface of a ship's deck. Curved fire from land batteries placed for the defence of channels is most effective, but such fire is impracticable in contests between vessels at sea, as an entire shipload of ammunition might be expended before making one successful shot.
When elongated shot fired from rifled guns strike the water, they tumble end over end and sink beneath the surface, and there is probably no instance known of such a shot striking a vessel below the water-line, unless her side was exposed by rolling. When the combatants are a certain distance apart, the intervening water serves as an impenetrable rampart for that portion of the ship below its surface. For every depression below the mean level of the water there is a corresponding elevation or protuberance above it; and these elevations or protuberances above the mean surface will most effectually deflect shot of high energy, and protect the side of the vessel below them; therefore, a vessel would not be exposed by the hollows between two waves, and if she was, a plane-sided shield would have no advantage over a curved one.
Referring to the drawings, Figure 1 is intended to illustrate the great superiority of the curved deflective shield over any other form of armor for water-line defence, in that it conforms to the arc of a circle in cross section, and presents, as the ship rolls, a practically constant angle of impingement to horizontal shot.
The portion of a deflecting shield, of any form, liable to be struck at any given instant consists of a zone of small area situated above, at, and very slightly below the mean water-level. This small zone is shifting in character, and on a curved shield of five feet rise, extending four feet below and one foot above the water-line, it would probably be about 18” in height. The curved shield covers the entire zone of danger, five feet in height; and this smaller zone, consisting of the part liable to be struck by horizontal fire at any given instant, traverses the larger zone more or less, according to the oscillations of the vessel, and protects it in detail by constantly presenting a great horizontal thickness of armor, with a very acute angle of incidence, and a very large angle of clearance to the part where the vast majority of shot strike.
Figure 1 represents a cross section of a cruiser, and three different forms of deflecting shields, numbered respectively 1, 2 and 3. They each have the same immersion, being secured to the sides of the vessel four feet below the water-line, and numbers, 1 and 2 rise one foot above it; but the angle of the plane-sided shield no. 3 being equal to the angle of incidence of the curved shield no. 2 at the waterline, does not carry it to the same height.
No. 1 is the plane-sided shield proposed by the Naval Advisory Board for the cruiser Chicago, being the facsimile of the official drawing. This shield presents so large an angle to horizontal shot at the water-line that it will afford no adequate protection with the light plating of 12 inches proposed. Besides presenting too large an angle to give protection, it also weighs considerably more than nos. 2 and 3.
No. 2 is the curved deflecting shield—the form of water-line defence recommended by Act of Congress of August 5th, 1882, authorizing construction of new cruisers—conforming in cross section to the arc of a circle, and presenting a practically constant angle of impingement to horizontal fire at the water-line as the ship rolls, and that so acute as to make penetration very difficult with comparatively light plating.
A horizontal shot at the water-line would strike the curved shield at G; as the line IT is tangent to the arc at the point of initial impingement, it therefore represents the angle of the same.
The fact being that more shot would strike the curved shield above the water-line than below it, it is therefore making a concession to take G as the average angle, as, practically, the mean angle would be much less; and it should also be remembered that G is the initial angle of impingement, which, owing to the curved surface, rapidly diminishes as the shot glances along the plate. Such a curved shield would therefore possess a much greater deflecting efficiency than a plane sided one, presenting the same angle of impingement, like nos.1 and 3, the angles of which would not decrease as the shot glanced along their surfaces, but would be liable to buckle up in front of the shot and be pierced by it; a contingency that would not arise with the curved shield, presenting the same angle, as the shot, owing to the curve, can much more easily free itself from the surface of the armor.
Shield no, 3 is drawn for the purpose of proving that it is impossible to construct a shield, having plane inclined sides, that will present so acute an angle to horizontal fire as the curved shield no. 2; or that will give as much room under it for boilers and machinery; or that will exclude the same amount of water from the part of the vessel above it; or that will give the same strength and stiffness to a vessel.
The line AE' is drawn parallel to the tangent IT, and the horizontal water-line cuts it at H. As the line AE' is drawn parallel to the tangent IT, therefore the angles G and H are equal. And as this angle will not carry the crown of the plane-sided shield to the same height as the crown of the curved shield, the plane-sided shield will require a greater angle to attain the same height.
It will be apparent that the curved shield no. 2 contains under it the space represented by the segment contained between the arc AGE and its chord AE', in addition to that contained under the plane-sided shield no. 3.
Also as the segment is above no. 3 and below no. 2, the former will admit a volume of water into the ship above it, equal in cross section to the area of the segment AGEAE', to endanger the buoyancy and stability of the vessel, which the round-up of the curved shield no. 2 would exclude.
The curved shield no. 2 is superior in these particulars to the plane-sided shield no. 1, or any other plane-sided shield, presenting the same angle, that can be constructed:
1st. It presents a more acute, and, practically, constant angle of impingement to horizontal fire, and one that with a moderate thickness of plating, if supplemented with coal or stores in water-tight compartments to augment the deflecting efficiency and exclude water, would afford a very substantial resistance to the fire of heavy guns, while the plane-sided shield would afford but a very small measure of protection.
2d. The plane-sided shield no. 1 would weigh considerably more than the curved shield no. 2, and would encumber a ship with the weight of armor without giving her the benefit of its protection.
3d. The curved shield, if anything like the same angle of impingement is presented, will contain much more room under it, for boilers and machinery, than an inclined plane shield, and is therefore admirably adapted for light draught vessels intended for service in the shoal waters of our Atlantic and Gulf coasts.
4th. With an equal angle of impingement, the round-up of the curved shield would exclude a large volume of water, which the plane-sided shield would permit to enter, and endanger the buoyancy and stability of the vessel.
5th. The curved shield will possess a much greater deflecting efficiency with any given angle, owing to the fact that the angle of clearance is a constantly increasing one, so that projectiles which would readily pierce a plane-sided shield can free themselves from the surface of the curved shield.
6th. The curved shield, tied in by the chords of its arc and supported on longitudinal and transverse bulkheads, in combination with the ship's cellular bottom and sides, will give a vessel an efficiency and strength as a ram that is unprecedented. A vessel so built would form a scientifically constructed floating girder, having such rigidity as would permit of her being engined with the highest power. The curved shield with coal or stores above it, to augment the deflecting efficiency and exclude water, thereby serving as a life-belt for the vessel, would make a ship almost unsinkable, while the plane sided one would be such an element of weakness that a vessel fitted with it could only with difficulty be kept afloat in action.
In regard to the deflecting efficiency of light plates, disposed at an acute angle, the British Admiralty have made experiments at Portsmouth within the last two years for the purpose of testing deck armor, proving that a two-inch iron plate, entirely unbacked, simply supported on beams, disposed at an angle of 10”, would resist the penetrating power of the 18-ton lo-inch gun; and that iron plates of three inches thickness, similarly placed, and disposed at an angle of 15°, would throw off shot from the same gun discharged from a distance of 100 yards.
If such good practical results can be obtained from iron plates, it is reasonable to expect that a much greater efficiency can be derived from homogeneous steel plates, combining hardness with toughness.
To determine the relative deflecting power of the curved and plane sided shields in the absence of any very extensive experiments on inclined plates, we can only reason from results obtained with vertical armor, and, hence, to form a fair comparison it is reasonable to suppose that in all cases the velocity of the shot, resolved in a direction normal to the plates, is entirely destroyed, and that the striking force in each case will be that due to a shot of the same weight moving normal to the plate with a velocity equal to the normal velocity of the shot moving obliquely to the plate.
In the diagram, Figure 2, draw the tangent to the curve at the water line, and lay off on the horizontal line a distance AO to represent v2, draw AC parallel and OC normal to the tangent OT; lay off OB equal to OC, drop the perpendicular BB, then OD will equal v2 sin?, ? being the angle of inclination of the tangent to the horizon. Proceeding in the same way with the plane-sided shield, denoting the corresponding lines by corresponding letters, O'D' will equal v2 sin?, where ? is the angle of inclination of the plane-sided shield to the horizon. The striking force exerted against the shields respectively will be represented by these lines multiplied by the same constant, and the relative protection afforded will be inversely as the lines, or as 5.4 to 1 in favor of the curved shield. But when it is taken into consideration that the curved shield allows the projectile to clear itself after striking, by a considerably increasing angle of clearance, between the curve OF and the tangent O T, it is evident that this ratio of protection will be considerably increased in favor of the curved shield.
The other method of comparing the relative efficiency of the two shields is to measure the metal that would have to be displaced to effect penetration. In the case of the curved shield the distance through WR is 9 3/16”, there being 10/16” greater distance through the metal of the curved shield than through a plane-sided shield presenting the same angle. The distance HI through the metal of the plane sided shield no. 1 is only 3 ¼”.
In the case of vertical armor, experience has demonstrated that the energy required to penetrate plates of different thickness is proportional to the square of the thickness of the plate ; and reasoning from this, we are led to conclude that in the case of inclined plates it will vary as the square of the distance measured through on a line making the same angle with the plate that the plate makes with the horizon.
Taking the shield before mentioned, the distance through, as measured on the water line, in the case of shield no. 1, is 3 ¼ inches, and in the case of shield no. 3 the distance measures 7 10/16 inches, and the efficiency of the two shields would be directly as the squares of these quantities, or as 1 to 5.4. But as the curved shield allows the shot in glancing to clear itself more readily than a plane shield, it will be much more efficient than the above proportion shows.
Notwithstanding the fact that the great superiority of the curved shield over the plane can be proved by unanswerable mathematical demonstrations. Lieutenant Very, in his able and interesting article, “The Development of Armor for Naval Use” (No. 25, Proceedings U.S. Naval Institute), takes peremptory ground in favor of the plane over the curved shield: but I propose to show that both his premises and conclusions are erroneous.
On page 527 will be found this statement in reference to the comparative merits of the two shields: “In the United States it has been made a matter of much discussion whether this alteration from a curved to an angular disposition is an improvement or a step backward. It seems, however, to be easily susceptible of proof that the angular arrangement presents most decided advantages.” Upon the same page is a diagram representing a curved and a plane shield on the same cross section, with the outline of a boiler in position under them, for comparison. The top of the plane shield is represented as entirely below the water line, while the crown of the curved one rises far above it; but fairness of comparison in boiler capacity, under the two shields, required that both should have been given the same vertical height.
A casual, or an unscientific reader, from “a great respect for official utterances,” might give this unqualified claim of “most decided advantages” of the plane over the curved shield, its face value, but a critical examination of the diagram with its explanatory context will show the claim to be unfounded. It is generally true that any theory is “easily susceptible of proof” where its advocate is allowed to make his own premises, but Lieutenant Very has failed even to draw correct conclusions from his voluntary assumptions.
The only special advantage claimed by Lieutenant Very—with the aid of his incorrect diagram—which can be conceded, is a very slight decrease of angle of the plane over the curve at a point four feet below the water line, where projectiles virtually never strike. But when it is considered that this slight disadvantage for the curved shield, at the point mentioned, is accompanied by a corresponding decrease of the angle of curve over the plane at the top of the shield, where essentially all projectiles do strike, this very slight advantage is conceded, admitting for this argument Lieutenant Very's delusive diagram. I am not advocating protection to that part of a ship where it is practically invulnerable to shot.
There have been winds so fierce as to destroy the strongest structures on shore, and there have been storms so violent as to founder the staunchest ships at sea, and lightning so powerful as to make sport and fragments of either. Against such unusual incidents, intense as is the love of life, it has not been within the power of human thought adequately to provide. If men should seek to do it they would never build ships nor houses, but live in caves, and then not be absolutely safe from these immeasurable and irresistible forces. Such dangers are the inevitable risks of our living at all, and we build ships and go to sea in them, and build houses and live in them, and take these risks, and we would be mere savages if we did not. In this category of extremely improbable chances would come the likelihood of a ship being struck by a projectile four feet below the water line during an engagement. Such a thing may happen, but experience shows that it is no more likely to occur than the disasters of nature mentioned above.
If the curved and plane shields, represented in the diagram on page 527, were correctly shown as of equal height, the advantage in weight would be in favor of the curved; but the advocates of the plane are welcome to the infinitesimal advantage in this respect apparently obtained by the diagram.
This drawing also contains the outline of a boiler in position under the shields, and the statement has been repeatedly made, by members of the Advisory Board, that the curved shield will not cover as great a height of boiler as the plane-sided one. This assertion is also incorrect, as an inspection of the diagram will show. If the boilers are set close out against the side of the vessel, no advantage whatever in height of protected space would be obtained by the curved shield, as the top of the boilers would have to be placed more than four feet below the water-line, the same as when placed below a flat, under-water, armored deck, similar to that of the Comus class. The top of the shield being placed below the waterline, if the sides of the vessel should be penetrated, then when the water- excluding stores are exhausted from the compartments above it, the Comus flat-deck would permit water to flow in and sink the vessel. The top of the shield should rise somewhat above the waterline in order to give the vessel a margin of buoyancy independent of the water-excluding stores.
If the boilers are placed part way out, in the position shown on the diagram referred to, only a small measure of protection is obtained by the shield, owing to the large angle of incidence presented.
But any one can see, by referring to the diagram on page 527, that if the boilers are placed in their proper position, in the centre of the vessel, the curved shield there represented will cover a much higher boiler than the plane-sided one. Lieut. Very, therefore, in constructing his diagram “builded wiser than he knew.” Such a disposition of the boilers will give the following advantages over that shown in the diagram, viz. it will admit of a central longitudinal bulkhead, dividing the under-water body into water-tight compartments, a device with which all large vessels should be provided ; it affords greater safety to the boilers from the attack of torpedoes and rams in time of war, and danger from collision; it enables the firemen to obtain coal from side bunkers, or chutes from compartments above, directly in front of their furnace doors.
A large proportion of the coal and stores should be carried in the compartments above the shield, the effect on the stability of the ship being compensated for, when occasion requires it, by the admission of water to the double bottom. This would allow nearly all the space under the shield to be utilized for boilers, fire-rooms, machinery and magazines, with passages from the same to the different guns. The stout tubes for training the vertical V shields by power applied beneath the shield, also serve as conduits for conveying ammunition directly to the breech of the guns. By this means all exposure of men by the transportation of ammunition along the open deck is avoided.
Lieutenant Very makes the following statement on page 529: “It has been shown heretofore that a thickness of armor for the shield of less than four Inches can scarcely be depended on at a greater angle than 20°. The average angle necessary for this shield is from 22° to 28°.” These statements are strictly true, yet he, with a knowledge of these facts, proposed to apply 1 ½” thickness of plating to all the new ships in the form of plane shields disposed at an angle of 27°, having a horizontal thickness of only 3 ¼”, while a curved shield of considerably less weight, covering boilers of equal height, would present an angle of only 13°, and a horizontal thickness at the waterline of 9 3/16”, which would afford eight times the resistance of the plane.
An examination of the next statement on page 529 proves it to be widely incorrect: “Where a two inch deck curved with a single radius is put in, the same weight would allow with the chord disposition, 4 inch plates on the side chords and 1 ½ inch on the dead flat.” Taking the cruiser Chicago, the ship of greatest beam, and therefore the one most favorable for the above hypothesis, we find the area of the flat top is not more than one-eighth greater than the area of the side planes. It would therefore be impossible to increase the thickness of the side planes more than 5/8 of an inch by taking a half inch from the flat top, although two inches are claimed. In the ships of less beam, Boston and Atlanta, a half inch taken from the flat top would not increase the thickness of the side planes as much as 5/8 of an inch.
If the thickness of the sides of the plane shield can be augmented at the expense of the top, so likewise can the sides of the curved shield be increased in thickness at the expense of the top, by the application of taper plates; it is therefore not worth while to take this feature into consideration when comparing the merits of the two shields.
In a plane shield of such light plating as 1 ½”, disposed at so large an angle as 27°, the resistance would be so small in comparison to the power of the guns likely to be brought against it, that the full effect of the horizontal distance through the plating would not be obtained; as the tendency, in such cases of disproportioned resistance to projectile force, is for the shot to turn in a direction normal to the surface of the plate, as there is a less thickness of metal under the projectile than above it, and passing through the plating it moves in the direction of the less resistance. Therefore, such a weak shield, aside from its affording no adequate protection, would be a positive source of danger in itself from the downward deflection of projectiles; while a curved shield of equal thickness and less weight, presenting a much more acute angle of incidence, with a constantly increasing angle of clearance, would invariably deflect shot upwards.
Figure 1 is a fair and correct diagram for comparing the merits of the curved with the plane-sided shield, as both are of the same height, each being secured to the sides of the vessel four feet below the water line, and rising one foot above it.
With such a curved shield as no. 2, Figure 1, of two inches thickness of plating, the horizontal distance through the plating on the water line would be 12,25”, and the angle presented at the same point would be 13°, while the horizontal distance through a plane-sided shield similar to no. 1, Fig. 1, of that same thickness of plating, would be 4.33”, and the angle presented would be 27°. This angle would of course be the same at all depths, and would be the average of the angles in all positions, which would sometimes be greater and sometimes less.
The horizontal angle of incidence of the curve would be practically constant in all positions, and the horizontal thicknesses of plating, and ratios of superiority of the curve over the plane at different points of immersion, would be as follows, viz.
| Horizontal thickness | Superiority of curve over plane |
6” above water line | 18.5” | 18.31 to 1 |
Water line | 12.25” | 8 to 1 |
6” below water line | 9” | 4.32 to 1 |
12” below water line | 7.75” | 3.2 to 1 |
24” below water line | 6.25” | 2.08 to 1 |
30” below water line | 5.5” | 1.61 to 1 |
36” below water line | 5.25” | 1.41 to 1 |
42” below water line | 5” | 1.33 to 1 |
48” below water line | 4.75” | 1.15 to 1 |
From the above list of horizontal thicknesses of plating, and ratios of resistance at different depths of immersion, it will be seen that one of the chief merits of the curve is that it keeps its greatest angle and least thickness of plating safely submerged at a considerable depth below the water line, where shot cannot strike it; but where protection is most required, the curved shield gives the greatest thickness of plating, the most acute angle of incidence, and the largest angle of clearance, automatically adjusting the same as the vessel rolls.
A curved shield of two inches in thickness, presenting an angle of 13” at the water line, and a horizontal distance through the plating of 12.25”, would give double the resistance of a plane-sided shield of 4” thickness presenting an angle of 27°, and having a horizontal distance through the metal of 8.66”, as the squares of these numbers would be 150 and 74.99, or a ratio of 2 to 1 in favor of the curve, omitting the advantage of the large angle of clearance afforded by the curve; which also applies to all the ratios.
At the instance of Chief Constructor Theodore D. Wilson, who appreciates the superior merits of the curved shield, the Honorable Secretary of the Navy caused a modified form of it to be adopted in the plans for the cruiser Chicago. The plans for the Boston and Atlanta still contain the plane-sided shield.
The flat, under-water, armored deck applied to the Comus class of the British navy is in no sense a deflecting shield, as it cannot be struck by shot, being intended merely to resist the more direct downward impact of the fragments of shell, exploding within the vessel, above it. The Comus deck has no more curve than is given an ordinary deck for drainage, and it is so far below the water line that it does not give the room under it for boilers and machinery, which the curve, rising above the water line, affords; and, for the same reason, it does not give the margin of buoyancy which would keep the ship afloat in the absence of water-excluding stores.
The plane shield is a foreign modification of the curve, having been applied to the Leander class of the British navy as late as 1880; while the curved shield is a domestic product, having been designed by the writer of this article more than 20 years ago, when serving in Farragut's squadron; and was the result of his observation of the effect of shot on vessels in actual combat, and he asks no consideration for it on any ground other than its merits.
Figure 3 represents a cross section of a cruising vessel of 48 feet beam and 19 feet mean draught, in which the water line is defended by means of the curved deflecting shield no. 2, heretofore described, in combination with water-tight compartments above it to be packed with coal or stores, to augment the deflecting efficiency and exclude water, thereby serving as a life-belt to the vessel.
The cross section shown represents the compartments above the curved shield as packed with coal. The position of the curved shield in relation to the water line is to be adjusted before going into action, by the admission of water to the double bottom. The cellular sides of the vessel BB, between the curved shield A and the gun deck above it, are represented as packed with cotton, chemically prepared to resist fire, which would, by its elasticity, close shot holes and exclude water.
Figure 5 represents the curves of reserve and decreased buoyancy, for the purpose of showing that a vessel having a curved deflecting shield, rising slightly above the water line amidships, and having water-tight compartments above it packed with coal or stores, covering and protecting the under-water body, could have the sides of the vessel above the shield completely open to the sea, without destroying her buoyancy.
Figure 6 represents a cross section of a cruiser fitted with a deflecting shield rising one foot above the water-line amidships, and attached to the sides four feet below it.
We will now suppose the sides of the vessel to be shot through, allowing water to enter into all of the compartments comprising the space GTR over the shield, in which water-tight compartments coal and stores are packed, capable of occupying three-fourths the volume.
The water flowing in fills up the other fourth of the space GWT—which is interstitial—and when it has risen as high as the load water-line WT, the decreased buoyancy reaches a maximum equal to the weight of water filling one-fourth the space WOT, as shown on the curve by the ordinate AO. As the vessel sinks and the water continues rising in the life-belt of the ship—that is, the space above the water line and the curved shield—the stores in the life-belt displace a volume of water equal to three-fourths the space above the load water-line and the curved shield; combining this increase of buoyancy with the decrease of buoyancy due to the water which has entered the space IVGT, we obtain the curve AD, whose ordinate will represent the loss of buoyancy due to the entering water. As the vessel sinks, however, the curved shield is constantly increasing the displacement, and the ordinates of the curve OB will represent the increased buoyancy due to this increase of displacement. This curve intersects the former curve at I, at which point the upward and downward forces are again in equilibrium, and the abscissa corresponding to the ordinate at I will give the distance the vessel will sink by having her sides perforated completely above the shield, allowing water to enter freely all the compartments of the lifebelt of the vessel. This abscissa is 2 5/8”, and the vessel cannot sink further without the curved shield being pierced, allowing water to enter below it.
In comparing the plane shield, having inclined sides, with the curved shield, the relative structural strength of the two should not be lost sight of. In the curved shield, strengthened by curved beams and having the space over the shield and the berth deck divided by bulkheads, greater lateral and transverse strength can be given a ship than can be attained in any other way.
We will next consider the most desirable forms and arrangements for deflecting shields for guns. These are not simply shields, but are in fact armored gun-carriages, the guns being supported and trained upon them. Referring to Figure 3, C represents a cross section of a vertical V gun-shield closed at the rear, with a 10 ½-inch wire wound pivot gun mounted on it en barbette. Figure 7 represents a plan view of the same gun and shield.
This gun-shield is to be constructed of steel plates curved to the form shown on the plan view Figure 7, and disposed vertically to deflect sidewise shot that come from the direction in which the gun is trained. The gun has no lateral motion of its own independent of the shield, consequently when the gun is trained to deliver its fire, the shield is at the same time trained to the most favorable position to deflect shot coming from that direction, the angle presented to the line of fire being very acute.
The gun is mounted by trunnions on a compact metal carriage, resting on slides bolted to the sides of the shield. The recoil is received on hydraulic buffers. The amount of recoil allowed for is three feet. The top of the shield, except a space at the breech of the gun, is covered by plating of two inches thickness.
The vertical armor is formed of two thicknesses of steel plating; one enveloping the entire shield is of five inches thickness, and is reinforced at the forward end of the shield, where the angle is greatest, by an inner plating of three inches thickness. The two layers of plating form a shield of eight inches thickness, which at the acute angle presented will be impossible to penetrate with any gun now in use. These shields would be improved by constructing them of taper plates of single thickness, the greatest thickness being placed at the forward part of shield where the angle is greatest; thereby equalizing the resistance of the shield.
The shield and gun are mounted on a deflecting turn-table of eleven feet eight inches diameter, the outer edge of which is shaped like a double convex lens; the office of which is to protect defectively the conical anti-friction rollers upon which the shield rests. This lens shaped turn-table is composed of two parts, being divided by a horizontal and a vertical line, as shown by C on the cross section drawing, Figure 3.
The lower plate D of the deflecting turn-table is secured to the deck of the vessel, and in it are fixed the conical anti-friction rollers upon which the shield rotates. The metal of the lower plate, immediately under the rollers, is cut away, in order to prevent an accumulation of sand or dirt which might clog them. The outer edge of the upper plate F embraces the lower plate D, thereby giving it a firm lateral support. So that no inordinate strain would be thrown upon the rotating pipe E by the rolling of the vessel, or the shield being struck by projectiles.
The lower plate D has a circular aperture in the centre through which rises the rotating and conduit pipe E from beneath the curved shield A, protecting the water line.
The pipe E is secured to the upper plate F of the deflecting turntable, which in turn is secured to, and forms a part of, the bottom of the shield. Consequently when the pipe E is turned, the shield and gun, on the deck above, are turned with it.
The shield and gun are trained by a pair of pneumatic engines G; pneumatic engines are preferred to steam on account of the exhaust exercising a cooling and ventilating influence. An endless screw on the shaft of the engines engages in a worm wheel secured to the end of the rotating pipe E, thereby turning the pipe, shield and gun in either direction with facility.
The pneumatic engines G are fitted with link-motion valve gear, with the lever H controlling it inside the shield, at the breech of the gun, convenient to the hand of the captain thereof, who trains the gun and shield by the lever without the intervention of any other person.
The lever is so arranged that when it is in the position a, the valves of the rotating engines are thrown into position to train the gun and shield in one direction; when in the position b, the valves are closed and the shield stationary, and when in the position c, the valves will be thrown open to train the gun and shield in the opposite direction.
This training apparatus has great power, there is therefore but little danger of the shield being jammed fast by any obstruction. It will also hold the gun and shield firmly in any desired position, notwithstanding the rolling of the vessel.
Referring to Figure 3, I represents a cross section of the pipe by which the shield is trained, which also serves as a conduit for ammunition into the shield. This pipe is V shaped, as shown by the cross section, the object being to present acute deflecting surfaces to projectiles which might strike it. It will be seen that in all positions of the shield and gun the conduit pipe I presents a constantly open passage to the magazine, beneath the curved shield, protecting the water line.
The ammunition is passed up through the pipe I by means of the traveller K, which, in the drawing, shows a cartridge upon it; when it reaches the top of the pipe, inside the shield, it falls over into a little truck L ready to receive it. The traveller K is actuated by means of the crank O. The truck L is drawn out to the breech of the gun with the ammunition upon it, traversing the long arm of the lever M. The long and short arms of this lever are attached to a rock-shaft; the short arm is also attached to the connecting rod of a small hydraulic cylinder N, by means of which the ammunition is elevated to the breech of the gun upon the truck at the end of the long arm of the lever, as shown in the drawing. The loading lever M when in position to receive ammunition from the conduit pipe is upon the floor of the shield.
The space between the shield and the gun, when the latter is elevated, is kept closed to exclude machine gun missiles, by means of the port stopper P, pivoted to the shield directly under the gun, against which it is pressed by means of the spring Q, or a counterweight, thereby closing the space between the shield and gun occasioned by the elevation thereof.
These pivot gun-shields, while in action, should be kept trained so as to deflect projectiles even though the gun be not in use.
There is ample room in the pivot gun-shield for six men, while three men with the special appliances proposed can work the 10 ½” gun with facility and efficiency.
The total weight of the pivot gun-shield with the deflecting turntable, rotating pipe, rotating engines, elevating and loading apparatus, etc., is 65 tons and 20 lbs. But if the shield was made open at the rear it would weigh much less.
The weight could also be greatly decreased by making a shield of less thickness of plating, which would still give a very efficient protection.
The plating of the shield, shown and described, is 8 inches thick, sufficient at the very acute angle presented, if constructed of homogeneous steel, combining hardness with toughness, to deflect projectiles from any gun in existence.
Figure 8 represents a plan view of a vertical V shield of the broadside battery, the gun being trained at right angles to the keel of the vessel. Figure 9 represents a plan view of a similar vertical V shield, open at the rear, in which the gun is represented as being trained parallel with the side of the vessel. The cross sections of these V shields for broadside battery are represented by RR in the cross section of the ship. Figure 3. These V shields are mounted in bay window like projections, which, however, do not extend beyond the line of the ship's side at the water line, the vessel having considerable tumble home.
Broadside guns, mounted in this manner, can be trained so as to deliver fire almost directly ahead or astern.
These small V shields for the broadside guns are trained in the same manner as the large pivot gun-shield, being fitted with the same appliances, and mounted on a deflecting turn-table of similar form, and in addition are pivoted in the I beams of the deck above. The guns, however, are not mounted en barbette, but extend directly through the shields.
It is proposed to partition off the upper part of the shield by means of a metallic diaphragm, forming a compartment in the upper part for the accommodation of the gun-captain, who is to recline in a prone position; the diaphragm upon which he rests being well padded on each side to deaden concussion. From this position the gun-captain can see through the aperture S in the forward end of the shield, and can train his gun by means of the lever, controlling the valve gear of the rotating engines, beneath the curved shield. By the aid of these appliances three men, completely under cover, can load and fire a six-inch rifled gun with far greater rapidity and efficiency than a much larger number of men, exposed upon the open deck, working guns mounted in the ordinary manner.
In view of the great improvements recently made in machine guns of large size, firing percussion shell capable of piercing the sides of unarmored vessels at considerable ranges, it will be seen that a ship having her gun-crews protected in shields of this form will possess an advantage so great that it would doubtless be good policy to have fewer guns, so protected, than a greater number unprotected. In other words, the weight of the battery should be divided between guns and gun-shields, the weight of ammunition remaining the same. The armor of the broadside gun-shields is four inches at the forward end where the angle is greatest, and two inches at the rear end where the angle is very acute.
The weight of the broadside gun-shields of four inches thickness of armor, with the deflecting turn-table, rotating pipe, rotating engines, elevating apparatus, etc., is lo tons 760 pounds. But such a shield will give an efficient protection against the projectiles of heavy guns, while a shield of but little more than one-third the weight would give protection against machine gun fire, as well as against splinters, fragments of shell, etc., which occasion nine-tenths of the casualties; a small proportion are due to exposure of men in the direct path of large projectiles. The form of the vertical V shields affords protection to the gunners within them against the side splash of splinters and the spread of fragments of exploding shell, thus securing a great advantage over vertical armor, or guns mounted in a large casemate, as splinters and debris could devastate the interior of such a casemate from end to end, while light shields, which would offer no substantial resistance to heavy shot, would afford complete protection against splinters and fragments of shell; the protection obtained in this case against injury from shot by the subdivision of space being analogous to the protection afforded in the direction of buoyancy and stability, by the division of the underwater body into water-tight compartments.
Figure 10 represents a cross section elevation of a vertical V gun shield, with an 8-inch rifled gun mounted on it en barbette. Figure 11 is the plan view of the same. These figures illustrate the proposed method of mounting the pivot guns in the new cruising vessels. This shield is intended to be trained and the gun operated in the same manner as those heretofore described, being fitted with the same appliances; and they permit of the guns being fired either directly ahead or directly astern. As it is open at the rear end, it can be made of a proportionally less weight than the pivot gun-shield heretofore described. The plating is disposed in two layers; the outer one enveloping the entire shield is of three inches thickness, this is reinforced at the forward end, where the angle is greatest, by an inner plating of two inches thickness, making a total thickness of five inches. The best method for the construction of such shields would be by two taper plates.
The weight of this gun-shield with the deflecting turn-table, rotating engines, rotating pipes, loading apparatus, etc., is 32 tons 18 lbs., the weight of the shield itself being 18 tons.
If the deflecting turn-tables, upon which the vertical V shields rest, were supported above the wooden deck on short drums or cylinders of sheet metal a foot or fifteen inches high, which would give an efficient support, while affording no material resistance to shot, being easily penetrable, but very difficult to cut entirely away, the danger of the shield being jammed fast by shot tearing up the wooden deck would be entirely obviated.
The vertical V shields were also recommended for the new ships by the Act of Congress providing for their construction.
In considering the merits of these gun-shields, it should be remembered that the special appliances proposed will enable the guns of a ship to be operated with a much smaller crew; and, if the weight of the extra men required to work the guns by the present system, with all their belongings, and the provisions and water to sustain them, was credited to the shields, it would balance a large percentage of the weight entailed by them.
It will be seen that the armor of the proposed vessel is to be so arranged as to present no direct resistance to shot, but all the vital and offensive parts are covered by armor which protects defectively, and the areas of the cross sections of armor are reduced to a minimum in order to present the least possible target to shot.
Projectiles are permitted to pass freely through the vessel, on the principle that the less resistance offered, the less injury received. Shot entering the side of the vessel would plow through the coal or stores packed in compartments above the curved shield, and would be deflected upward, that being the line of the least resistance, and would pass out through the far side of the vessel considerably above the water line.
As the men working the guns are all protected in appropriate deflecting shields, the upward flight of projectiles, after impinging on the curved shield, would not do any serious damage. Even though the upper works of the ship were riddled, she would not be seriously damaged, as her vitals would remain intact.
As the crown of the curved shield rises above the water line, it thereby protects the vital far side of the vessel, where heavy shell would otherwise do the greatest damage by exploding against the frames at, and below, the water line and tearing off entire plates, thereby admitting such great volumes of water as to engulf a vessel at once.
The five vital factors of a war-ship are the water line, the magazine, the motive power, the steering gear, and the personnel. In the proposed vessel, the first four of these and a part of the fifth are protected beneath the curved shield, the remainder of the personnel being protected in the deflecting gun-shields on the decks above.
The curved shield is no more difficult to construct than the plane sided one, and will cost no more. Nor does it present as much difficulty in construction as the skin plating of an ordinary vessel.
The writer is indebted to Naval Cadet H. G. Leopold, U.S.N., for the diagrams and drawings with which this article is illustrated, as well as for reading it before the meeting of the Institute.