ACR-10 Tennessee / CA-10 Memphis - Armor Protection
The increase in the weight of protection carried amounted to 30 per cent of that on the Pennsylvania class, and was devoted to an increase in the armor on the turrets and the redoubts of the 10-inch guns, which replaced the 8-inch guns in the forward and after turrets on the Pennsylvania class, and to an increased area of side armor, affording ample protection to the magazines and the supply of ammunition to all guns, and also to a complete subdivision of the main battery by armor bulkheads.
The speed of the Tennessee class was 22 knots, the same as the designed speed of the nine cruisers of the Pennsylvania and St. Louis classes, and was effected without an increase in machinery weights. These vessels will be exceeded about a knot in speed by a few foreign armored cruisers, but if their designs had been made upon the prime requisite of speed superior to all vessels of this category, it would have been necessary to sacrifice the battery and protection now assigned which enabled them to present a heavy preponderance of battle power over any armored cruisers yet designed elsewhere, and also enabled them to deal on occasion with a )arge proportion of existing battleships.
The draft of these vessels was limited by the depth of the harbors of the United States. The hulls were of steel, with the usual cellular subdivisioning. The inner bottom was continued from the keel to the protective deck, at each side, and extended forward and aft to about the knuckle of the keel, so that the vessel was thoroughly protected from injury in case of grounding, throughout any point in their length. The freeboard of these vessels at the line of the main deck was about 18 feet, amidship, 24 feet, forward, and 21 feet 6 inches aft. By reason of the high freeboard, commodious quarters are provided for all officers and men above the water-line. The conning-tower, located on the lower bridge, is one deck higher than in earlier designs.
The hull was protected by a 5-inch belt of armor extending from five feet below the normal water-line to the upper deck in wake of 6-inch guns, this armor extending to the bow and stern near the water-line to form a water-line belt, being reduced in thickness at the ends to three inches. Extending from the gun deck to the protective deck are bulkheads of 5-inch armor, which form the forward and after limits of the belt armor. Between the gun and berth decks are similar bulkheads located in wake of the 10-inch barbettes which are fitted on the gun deck and form the forward and after limits of the side armor between the main and gun decks. Above the gun deck, in wake of the 3-inch battery, 2-inch nickel steel is fitted. The 6-inch guns on the gun deck are isolated by splinter bulkheads of 1-1/2-inch nickel steel, extending continuously across the ship, and 2-inch nickel steel extending fore and aft.
The 10-inch turrets were protected by nine inches of armor on the sloping face, seven inches of armor on the sides, five inches in the rear, and with top plates of 2-1/2-inch nickel steel. The barbette armor is seven inches thick in front, reduced to a thickness of four inches at the back and below the gun deck, where protected by the belt and casemate armor. The protective deck, which extends from bow to stern, was one and one-half inches thick on the flat, over the engine and boiler spaces, four inches thick on the slopes at the side, extending down to the bottom of the belt armor, three inches on the slope, forward and aft. A cofferdam, thirty inches thick, was worked from end to end of the vessel between the protective and berth decks. These cofferdams were filled with water-excluding material.
To compare the Tennessee and battleship Connecticut, for example, the same principles are applied in the distribution of armor in the one as in the other ; namely, a water-line belt 5 inches thick ; casemate armor, continuous with the belt and of the same thickness, completely enclosing the broadside battery ; protective-decks ; turrets with 7-inch sides and 5-inch back, and 9-inch port-plates ; 7-inch maximum on barbettes ; splinter-bulkheads, conning-tower, armored tubes, etc., all being very much lighter in the armored cruiser than in the battleship.
Wood work was reduced to a minimum, and all such above the protective deck, except deck planking, armor backing, furniture, and a few minor items, were fireproof.
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