The shell is a little smaller than the bore of the gun, but near its base it has an encircling band of soft copper, which band is a tight fit in the gun. The soft copper crushes into the "rifling," whereby the shell obtains its spinning action. The large guns are mounted in pairs, each pair on a turntable, by the movement of which to right or left they are trained upon the distant target. The turntable is surrounded by a wall of thick armour and is covered by an iron hood or roof. In addition to being turnable to right or left, there is, of course, provision for raising or depressing the direction in which each gun is pointing. They need always to point more or less upwards, and the particular angle depends upon the range or distance of the object aimed at. This is ascertained by range-finding instruments and communicated to the officers in the turrets, as the covered turntables are called. The guns are then elevated or depressed to suit the range. Each gun rests upon a cradle which is itself fitted upon a slide. When it is fired it "kicks" backwards, against the force of a buffer of springs, or a hydraulic or pneumatic cylinder. Thus after each shot the gun moves backwards upon the slide, but the hydraulic apparatus brings it back again into position for firing almost instantaneously. In naval guns all the movements, including that of the turntable, are by power, either hydraulic or electric, or a combination of the two. The loading is also by power. The shells and ammunition are kept well down towards the bottom of the ship, under each turret. Lifts bring them up from there to a chamber just beneath the turntable, known as the working chamber. Here a small quantity only is kept, and that for as short a time as possible before it is sent up by other hoists straight to the guns themselves. The hoists are so arranged that, no matter how they may be elevated or depressed, the ammunition is delivered exactly opposite the breech, as the rear end of a gun is termed. Then a mechanical rammer pushes it straight in. [Illustration: RIFLES OF DIFFERENT NATIONS (_See_ Appendix)] The breech of the gun is closed by a beautiful piece of mechanism called the breech-block. It is really a huge plug which securely closes the end of the gun, a partial turn after it is in place fixing it firmly enough to resist all the force of the explosion. Yet it can be freed and swung back upon hinges in a few seconds. At the same moment that it is opened a jet of air blows into the gun, clearing out all effects of the recent explosion.