Page:EB1911 - Volume 20.djvu/266

Rh power, and a douche of water or blast of air, or a combination of both, removes any smouldering fragments of cordite or cartridge material before a fresh round is loaded.

Although there is little difference in principle between the arrangements of the mountings in the later “Majestics” and those in the “Dreadnought,” improvements in detail have enabled the interval between successive rounds to be reduced from about 55 seconds in the former case to 25 or 30 seconds in the latter.

In the turrets containing 9·2-in. and 7·5-in, guns, which exist in most British armoured and first-class protected cruisers, the moving weights are, of course, not so large, and, as might be expected, the assistance of hydraulic machinery is not necessary in so many operations. A drawing of a typical 9·2-in. gun and mounting is shown in fig. 92.

Training the turret and elevating the guns are, however, in all cases performed by hydraulic power, as is the raising of the projectiles to their place on the loading tray in rear of the gun, but the breech is opened and closed, and the charge and projectile rammed home, by hand power only, while the gun, after recoil, is forced out again to its firing position by means of springs. A ready supply of thirty-two projectiles is stowed in a “shell carrier,” which is a circular trough running on rollers round the turret, but independently of it. When a projectile is required to be loaded into the gun, the shell carrier is rotated until the required projectile is under a hatch in rear of the gun, when the projectile is raised by a hydraulic press on to a swinging loading tray. It is intended that the shell carrier shall be replenished direct from the shell-room during the pauses of an engagement. A new type of 9·2-in. mounting has been installed in the “Lord Nelson” and “Agamemnon,” in which greater use is made of hydraulic power with a view to improving rapidity of fire. In this mounting, each projectile is brought up from the shell-room as it is required, and the loading operations are performed by hydraulic power instead of by hand.

The “King Edward VII.” class of battleships and “Duke of Edinburgh” class of cruisers are the last ships in which any 6-in. guns have been mounted, and with the exception of the 7·5-in. guns in the “Triumph” and “Swiftsure,” these are the largest guns which are worked entirely by hand. Other hand-worked guns are the 4-in. and 12-pounder, which are mounted in small cruisers and destroyers.

The principles of the 6-in., 4-in. and 12-pounder mountings are similar. The rear part of the gun is partially enclosed in a metal cradle, which carries the recoil cylinder and running out spring box. The gun and cradle are balanced for elevation about trunnions on the cradle, which fit into trunnion bearings on the carriage. The latter carries the elevating and training gear, and the whole moving weight is borne by a pivot pin which rotates on a ball bearing. The gun recoils in the line of fire, and the energy of recoil is absorbed by means of the recoil piston, whose rod is secured to the gun, passing over a valve key secured to the cradle, in such a way as to produce a channel of varying sectional area through which the liquid in the recoil cylinder must pass from one side of the piston to the other. Springs run the gun out again after firing into its original position. The breech is opened by the single motion of a hand lever. A “bare” charge is used in the 6-in. and 4-in. guns, with the de Bange type of obturation, while a brass cartridge case has been retained with the 12-pounder, as with the earlier Q.F. guns.

Firing is by electricity, percussion being available as an alternative if required, and the current is usually taken off the dynamo mains of the ship.

Sighting.—The great advances recently made in accuracy of fire have been rendered possible, to a very great extent, by, the use of telescopic sighting apparatus. Arrangements are made in all modern sights for the bars or disks which carry the range graduations to be of considerable length or diameter respectively, in order that no difficulty may be found in adjusting the sights for every 25 or 50 yds. of range. In the larger hand-worked mountings, where the laying of the gun for elevation and for direction is effected by two men on opposite sides of the gun, the sights used by them are “cross-connected,” i.e. connected by rods and gearing to one another in such a way that, initial parallelism of the axes of the two telescopes having