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Secondary Battery

By the end of the 19th Century the guns of a warship were divided into two batteries, the main and secondary. The main battery included all the heavy guns, usually 12-inch to 9-inch. These guns were protected by armour and worked by machinery. The secondary battery comprised all the lighter guns which are distributed over the upper works and have less or even no protection ; these guns and their ammunition can be worked by hand. The 6-inch or 7-5-inch guns were quick firing, and were commonly arranged in broadside on the main decks in what is called a citadel, and a few on the upper deck. There were two distinct methods adopted to protect these guns - the casemate system and the side-belt protection.

The casemate system was largely adopted in the British Navy. Each gun is enclosed in a casemate which at the ship-s side forms a sponson to give the gun a large angle of train, about 140. Usually four casemates and, consequently, four 6-inch guns can be ranged on each side on the main deck. The guns in the forward and after casemates can fire directly ahead and directly astern respectively. On the upper deck there are usually two or three casemates on each side. Consequently a battleship with the 6-inch guns in casemates has seldom more than fourteen of these guns. The armor of the casemates is 6 in. thick on the outside and 2 in. on the rear walls. This protection is considered sufficient against the fire of 6-inch quick-firing guns.

The other method of protecting the 6-inch guns is by a continuous side-belt of armor, 5 in. to 7 in. in thickness, on the side ; screen bulkheads of 2 in. being erected between each gun, and at the ends of the citadel transverse armoured bulkheads are fitted between the main and upper decks. This is called the Open Box Battery arrangement. As many as seven guns on each broadside have been mounted by this method. The main disadvantage in this system is that the guns have not such a large angle of train as the guns in casemates, 110 as against 140, but the gun mechanism and gun crew are well protected from damage from gun-fire in the rear, and they have the advantage, that the guns and gun crews on one side are all under the supervision of the gunnery officers.

A system which still further reduces the chance of damage in rear was adopted on some battleships. This is the Subdivided Box Battery arrangement, in which a screen bulkhead of 1 in. to 2 in. in thickness is worked fore and aft in rear of the guns, and this, with the screen bulkheads between each gun, completely isolates each guu and gun crew. The tactical advantage of control which the open box-battery gives is, however, sacrificed in this arrangement.

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