a consequently increased muzzle velocity. The latest type,
which is known as the Mark XI., and is mounted in the " Lord
Nelson " and " Agamemnon, " is 50 calibres in length, weighs 28
tons, and with a charge of cordite of 130 ℔ gives to a projectile
of 380 ℔ a muzzle velocity of 2875 ft. per second. The 7·5-in.
gun forms the secondary armament of the "Triumph" and
"Swiftsure," and is mounted in the armoured cruisers of the
"Minotaur," "Duke of Edinburgh" and "Devonshire"
classes. The 6-in. gun, of which there are a very large number
afloat in modern, though not the most recent, battleships, and
in armoured and first and second class cruisers, is the largest gun
which is worked by hand power alone. For this reason, and on
account of its rapidity of fire, it was for many years popular as
an efficient weapon. It was evolved from the 6-in. 80-pounder
B.L. gun, constructed at Elswick, which was the first breech loader
adopted by the Royal Navy, and whose development has
culminated in the 6-in. Mark XL gun of the " King Edward
VII." class and contemporary cruisers, which fires a 100-℔
projectile with a muzzle velocity of 2900 ft. per second. It has
only now passed out of favour on account of its inferior hitting
power at long range as compared with that of guns of larger
calibre, and as a secondary armament of 6-in. guns is still being
included in the latest battleship designs of more than one foreign
navy — notably that of the Japanese, with their practical experience
of modern war at sea — its abandonment in the British Navy
can scarcely be considered final. The 4-in. Q.F. gun is mounted in
the third-class cruisers of the "P" class as their main armament,
and an improved gun of this calibre, with muzzle velocity of
about 2800 ft. per second, is mounted in the later " Dreadnoughts,"
as their anti-torpedo-boat armament.
The increase in size of modern torpedo craft and the increased range of modern torpedoes has led to a reconsideration of the type of gun suitable for the protection of large ships against torpedo attack. The conditions under which the anti-torpedo boat armament comes into play are the most unfavourable possible for accurate gun-fire. The target is a comparatively small one; it comes into view suddenly and unexpectedly; it is moving rapidly, and the interval during which the boat must be stopped, i.e. that between her being first sighted and her arrival at the distance at which she can expect to fire her torpedo with success, is in all probability a very short one. Moreover, in the great majority of cases the attack will be made at night, when the difficulties of rapid and correct adjustment of sights, and of range-finding and spotting, are intensified. Two requirements then are paramount to be satisfied by the ideal anti torpedo-boat gun: (1) it must have a low trajectory, so that its shooting will not be seriously affected by a small error in the range on the sights; (2) one hit from it must suffice to stop a hostile destroyer.
For many years it was considered that these requirements would be met by the 12-pounder, which was the anti-torpedo-boat gun for battleships from the "Majesties" to the "Dreadnought," the 12-pounders mounted in the "King Edwards" and the " Dreadnought " being of a longer and heavier type, giving a higher muzzle velocity. The introduction of a larger gun has, however, been considered desirable, and a 4-in. gun of new type is mounted in the later "Dreadnoughts," while in the older battleships and large cruisers with secondary armaments it is considered by many officers that the 6-in. guns will prove to be the most effective weapon against torpedo craft. The gun armament of destroyers being required to answer much the same purpose as the anti-torpedo-boat armament of large ships, namely, to disable hostile torpedo craft, the type of gun used has followed a similar line of development.
Starting with 6-pounders in the first destroyers built, the majority of the new destroyers have a fixed armament consisting of one 12-pounder forward, and four 6-pounders. This armament has been changed in the larger destroyers to one of 12-pounders only, while the latest ocean-going destroyers have two 4-in. guns. Owing, however, to the strength of the decks of such craft being insufficient to withstand the stresses set up by the discharge of a gun giving very high muzzle velocity, the 4-in. gun for use in light craft is one giving 2300 ft. per second muzzle velocity only and has a very long recoil. The 6-pounder and 3-pounder Q.F. guns arc no longer being mounted as part of the armaments of modern ships. A very high rate of fire was attained in the "semi-automatic" mounting of the 3-pounder, which was last fitted in the " Duke of Edinburgh " class, but for reasons already given guns of this type are no longer required, and the 3-pounder is retained only as a boat gun for sub-cahbrc practice.
All double-banked pulling boats and all steam-boats are fitted with arrangements for mounting one or two guns, according to the size of the boat; the object of the boat armaments being for use in river operations, for covering a landing, or in guard boats. Three descriptions of gun are used, the 12-pounder 8 cwt. and 3-pounder, light Q.F. guns, and the Maxim rifle-calibre machine gun.
Gun- Mountings.—Gun mountings in the British navy may be divided broadly into two classes, power-worked and hand worked mountings. The former class includes the mountings of guns of all calibres mounted in turrets or Vjarbettes, also of 9·2-in. guns mounted behind shields; the latter class includes mountings of guns of all sizes up to the 7-5-in. which are mounted in batteries, case mates or behind shields.
Hydraulic power has been adopted almost universally in the British navy for power-worked mountings, although electricity has been experimented with, and has been largely applied in some foreign navies. The principal advantages of hydraulic, as compared with electric, power are its comparative noiselessness and reliability, and the ease with which defects can be diagnosed and rectified. On the other hand, electric power is more easily transmitted, and is already installed in all ships for working electric light and other machinery, whereas hydraulic power, when used, is generally installed for the purpose of working the guns only. The 12-in. guns in the "Majestic" class, following the practice with the earliest heavy B.L. guns, were loaded normally at extreme elevation of 135°, and the turret had to be trained to the fore and aft Une and locked there for each occasion of loading. An alternative loading position was also provided, in which the guns could be loaded at 1° of elevation and with the turret trained in any direction. Loading in the alternative position could, however, only be continued until the limited supply of projectiles which could be stowed in the turret was exhausted. Experience showed that a greater rapidity of fire could be obtained by the use of this " all round " loading position, as it was termed, and in the latest ships of the " Majestic " class, and in subsequent battleships, the fixed loading position has been abandoned.
The details of recent 12-in. mountings vary considerably, a drawing of one of the most recent being shown in fig. 91, for which thanks are due to Messrs Vickers, Sons & Maxim, but in the majority of cases there is a " working chamber " revolving with the turret. A fixed ammunition hoist brings the shell and cartridges from shell room and magazine respectively into the working chamber, where they are transferred to a cage which takes them up, by hydraulic power, to the rear of the gun. The gun is strapped by steel bands to a cradle (see fig. 91) which moves in and out along a slide on recoil, the gun always remaining parallel to the slide. Gun, slide and cradle are pivoted for elevation on trunnions carried in trunnion bearings fixed to the structure of the turret, and the whole moving weight is balanced with the gun in the "run out" position. The recoil of the gun on firing is taken up by a hydraulic press placed underneath the slide, and the gun is run out again into the firing position by hydraulic power. Loading is carried out by means of a hydraulic rammer, with the gun in the "run out" position, and at an angle of elevation which varies with different mountings. In the most recent mountings loading can be carried out with the gun at any elevation, thus affording considerably greater facility to the gunlayer for keeping his sights on the target during the process of loading, and so increasing the rate of fire by enabling the gun to be discharged immediately the loading operations are completed. Elevating is by hydraulic power, and is effected by cylinders placed underneath the slide, the pistons worlcing on an arm projecting downwards. Turret turning engines are also hydraulic, and much attention has been given of late years to the perfection of elevating and turning gear such as will enable the turret or gun to respond instantly to the wish of the gun-layer, and to move either with considerable rapidity, or very slowly and steadily as would be the case when following a target at long range and with but little motion on the ship. The breech is opened and closed by hand or by hydraulic
