In presenting the subject of “ Armored Turrets for Coast Defense ” to this Institute, I am indebted to the Gruson Iron-works, a company incorporated under the laws of the State of New York, for valuable information, model and plans, by which I hope to make clear the construction and peculiar merits of this class of gun-protection.
I wish it understood, however, that this is not an undeveloped and untried inventor’s ideal, but an advanced and fully perfected system, which has long since passed the experimental stage and has been adopted by most of the foreign governments, after years of extensive experimenting and the expenditure of millions of dollars.
The present seems an appropriate time to present the matter to the scientific public, since, for the first time, it is possible to produce these turrets in this country, of American material, and made by American workmen, owing to an agreement entered into between the Gruson Iron-works and the Fried. Krupp Grusonwerk, of Magdeburg-Buckau, Germany, where they have hitherto alone been manufactured. Although its full development and present perfection have been attained at the German works, it may be of historic interest to state that the first idea of using a rotating protected platform for large guns originated with Mr. Theo. Ruggles Timby, a native of the State of New York, who filed a caveat in 1843 for a “ metallic revolving fort, to be used on land or water, and to be revolved by propelling engines located within the same and acting upon suitable mechanism.” This was followed in 1862 by the issuance to Mr. Timby of two patents (No. 35,846 and No. 36,593) covering the ideas described in his caveat of 1843. The first practical application of this system was made on the “ Monitor,” of Civil War fame, Mr. Timby receiving $10,000 for two turrets as royalty for the use of his invention by John Ericsson, to whom this construction is usually, but erroneously, ascribed.
The manufacture of Gruson armor has been closely watched by our government for the past fifteen years; its merits having been recognized in the official report of the “ Endicott Board ” made in 1886, in which the system is spoken of as being well adapted for the needs of our coast defenses at certain points. In the report of the “ Board ” (printed as Executive Document No. 49, first session, 
Forty-ninth Congress) they say that the shore-batteries may be revolving turrets, and they recommend such turrets as a part of the proposed defenses of the ports of New York, San Francisco and Boston, besides Hampton Roads, Narragansett Bay and Key West. The report recommends at the above places the installation of nine 2-gun turrets for New York; five 2-gun turrets for San Francisco; four 2-gun turrets for Boston; two 2-gun turrets for Hampton Roads; one 2-gun turret for Narragansett Bay; and one 2-gun turret for Key West; making a total of twenty-two complete turrets.
Just before the publication of this report, a trial of Gruson armor was made by the Italian government at Spezzia. The trial-plate, weighing 193,895 pounds, was mounted against the solid rock, being flanked on either side by two junction-plates. It withstood four direct shots, at a range of 150 yards, from a 100-ton (16.93-inch) Armstrong gun, using Krupp steel projectiles; the result of the hits, which all landed in about the same place, being three abrasions, varying from 1½ inches to 4 inches in depth, and a number of fine cracks on the surface, none of which, however, showed upon the rear of the plate. All of the steel projectiles were shivered into thousands of pieces.
At this trial representatives of the United States Engineer and Ordnance Corps were present, and the test was considered absolutely conclusive by all the official representatives of the great powers. Since then Gruson turrets have been purchased and erected by the governments of Germany, Italy, Austria, Holland, Belgium, Switzerland, Roumania and Brazil. Some time ago there was an interpellation in the British Parliament by one of its members, by which the government was asked why there had not been any tests in England of Gruson turrets, to show their capability of withstanding heavy fire with the most approved modern ordnance and projectiles. The chief naval constructor answered: “We know enough of these turrets to say that where foreign coasts are protected by Gruson turrets British warships will not go.”
During the late war with Spain there was not sufficient time to obtain these turrets from Germany and place them in position, but now that we are again at peace, and the importance of defending our coast from enemies has been so clearly shown, it seems opportune to call attention to the means of defense adopted by foreign countries, indorsed with approval by our own officers sent abroad for the purpose of investigation.
What are Gruson turrets ? What do they look like ? Of what are they made, and what makes the protection they afford so complete ?
These questions can best be answered by imagining two big coast-defense guns, say of 12-inch bore, or perhaps even of 16- inch bore, such as the monster gun just completed at Watervliet Arsenal and soon to be tested at the proving-ground at Sandy Hook, in New York harbor. In the Gruson turret two such guns are placed side by side on independent carriages, and the latter are set up on a platform of steel construction with all the necessary apparatus for changing their angle of elevation, upon which depends the range, also for hoisting their ammunition from the bomb-proof below, for opening and shutting their breech and ramming in the ammunition. Imagine all this apparatus on a turn-table to allow the guns to send their fire in any direction by a simple rotation of the platform, and you can obtain some idea of the appearance and operation of the turrets. There is need of protection for guns and men, not only in front and on both sides but overhead as well; for the accuracy of modern naval ordnance permits of sending projectiles from considerable distances so aimed as to reach the point of delivery under angles from above, striking behind ramparts of earth or stone in such a manner as to destroy and dismount guns and any machinery connected with them.
Explosive shell and shrapnel can be fired so accurately, and their explosions in the air regulated so well, that they will burst directly over the heads of the gunners and hurl their missiles straight upon them. The Gruson turret, in exposed and well-advanced positions, at or about the sea-level, furnishes abundant shelter from all these kinds of attack. It is shaped like the shell of a turtle, and is mounted over and around the guns and their men, leaving only two port-holes just large enough for the gun-barrels to protrude, and a small lookout in the top-plate for sighting them. This protective shell consists of a number of sectors, varying according to the size of the turret, forming the circumference of the flat dome or cupola, and two half-circular plates forming its roof, the sectors giving protection on the breast and the roof-plates giving protection overhead. The dome rests on a substructure made of steel plates and strengthened with angle-irons. Heavy steel beams run across this substructure to carry the carriages on which the guns are mounted. The substructure is further provided with a roller-path of cast-iron, resting on a number of conical flanged steel rollers, the axles of which have their bearings in a live ring which keeps them in proper relation to each other. The conical shape of the roller allows them to revolve, without the aid of a central pivot, on a stationary roller-path imbedded in the masonry.
The cupola is surrounded by the so-called “ glacis-armor ” which forms a ring of double-curved chilled cast-iron plates somewhat similar to those used for the cupola, but which are set upon solid masonry, are stationary, and protect the substructure, gun-carriages, and the machinery by which the turrets and guns are operated.
The glacis-armor is itself further protected by a construction of granite and concrete. The cupola can be revolved either by hand-, steam-, hydraulic, electric or other motive-power, as may be most convenient.
To revolve the turret by hand a capstan is provided, which transmits its revolutions through gearing to a pinion and racer fastened to the upper roller-path. Turrets for the larger sizes of guns are generally revolved by steam-power, for which purpose a two-cylinder engine is placed in the lower gallery. The starting-lever for the engine is operated from the middle gallery. Both hand- and steam-power can be made interchangeable by suitable mechanical apparatus, thus providing against the contingency of the failure of either.
In order to stop the turrets from revolving spontaneously, especially when the guns are fired singly, a suitable brake is attached to the substructure, consisting of hydraulic cylinders
controlled by proper valves, whose pistons press against a brake-ring cast on the lower path provided for this purpose. Hydraulic cylinders are connected by pipes to a pressure-transformer in the center of the turret.
The dome is perforated by two port-holes through which the guns operate side by side, and which so closely surround them that no projectiles from the outside can penetrate into the interior of the structure. In order to make this possible, the
guns are mounted on special carriages, technically known as “ Gruson minimum port carriages,” which provide for the elevation and depression of the guns from a pivot near the center of the embrasure, instead of having these movements take place on the trunnions of the gun. Such an arrangement makes it necessary to lift a considerable weight with every change in the elevation of the gun, and for this purpose hydraulic accumulators are provided and supplied by a special set of high-pressure pumps.
The horizontal movement of the gun is effected by rotating the turret, the amount of such motion necessary to a proper sighting being regulated by the commanding officer, who has his station in the center of the cupola and makes his observations through an orifice in the dome or roof, in which is also provided a sighting-apparatus. A hoisting-and-charging mechanism is likewise provided, and operated by hydraulic or steam, as may be desired.
A reference to the illustrations will clearly demonstrate the general design and construction of the modern Gruson turret as now manufactured.
Fig. 1 shows a cross-section of the turret, gun-carriages and glacis-armor, together with the hydraulic-accumulators for elevating the gun-carriages.
Fig. 2 is a general plan and elevation for a turret to contain two 12-inch guns, and shows, in addition to the above, the arrangement and position of the pumps, boilers, rotary apparatus, ammunition-hoists and auxiliary machinery.
Fig. 3 gives detailed sizes of certain parts for the purpose of indicating the magnitude of the work. Some of the individual plates for a 16-inch turret will weigh about 90 tons, and great skill is necessary to successfully handle such a mass, with its subsequent special treatment and accurate machining. The revolving chilled cupola for a 12-inch 2-gun turret is composed of 14 plates having an aggregate finished weight of 1,667,000 pounds; the protecting stationary chilled glacis-armor being composed of 12 plates having a total weight of 1,175,000 pounds.
A cupola for a 16-inch 2-gun turret weighs 2,850,000 pounds and the glacis-armor 1,415,000 pounds.
The total finished weight of a 12-inch 2-gun turret, exclusive of the guns, is about 3,700,000 pounds, and of a 16-inch turret about 5,800,000 pounds.
The material used for the cupola and glacis-armor is a special quality of cast-iron, hardened by surface-chilling to a depth of 2½ inches or more. The plates or sectors going to make up a complete fortification are double-curved and of varying thick
nesses, according to their location, and are held together by means of embedded keys, no bolts or rivets being used.
The great mass and weight of the Gruson turret precludes its use for ship-protection.
When once established, the Gruson turret is easily maintained, owing to its simplicity of construction, its solidity and minimum risk of deterioration; and it requires less repair than any other kind of fortification, owing to the fact that the guns and carriages and interior structure are so thoroughly protected from the elements. In addition to this, it is the cheapest and most effective form of structure for gun-protection which can be adopted for low or advanced and exposed points, such as the entrance to the harbors of important cities, where high elevation cannot he obtained for the construction of the ordinary style of fortification.
These turrets are not intended to take the place of any existing form of fortification where the nature of the ground renders such fortification sufficiently effective, but are for use especially in localities where it is necessary to fortify points at or about the sea-level, and where its form would render it inconspicuous and present a very small target to an attacking enemy; since it is possible to render it almost indistinguishable from its surroundings, especially in the absence of buoys, lights, ranges, and the ordinary aids to navigation which are removed in time of war.