It is trained, or pointed in a horizontal plane, by turning the turret in which it stands but the correct elevation is gained by the use of telescopic sights. The principle of these sights is very simple. Imagine a graduated circle fixed to the side of the gun. Pivoted at the centre of the circle is a small telescope. The telescope can be turned round to any angle upon the circle and it can then be clamped at that particular angle. The range having been given to the officer in command of the gun from the range-finding station on another part of the ship, the telescope is set to the correct angle. Then the gun is elevated or depressed until the ship being aimed at is precisely in the centre of the field of view of the telescope, in other words, until the telescope is pointing exactly at the ship. Then the gun is fired. The effect, therefore, is this. The telescope always points (while the gun is being fired) at the object aimed at, but the gun is pointed upwards at a certain angle, which angle depends upon how the telescope is set upon the divided circle. Thus the setting of the telescope for a given range produces the correct upward tilt of the gun for that range. The breech-block carries a trigger and hammer arrangement whereby the firing can be done and also an electrical arrangement so that an electric spark can be employed. Both these firing contrivances are so made that they cannot be operated until the breech-block has been inserted and _made secure_. Thus a premature explosion is guarded against. CHAPTER X SHELLS AND HOW THEY ARE MADE Modern warfare seems to resolve itself very largely into a question of which side can procure the most shells. During the great war there was a time when the British and their allies were hard pressed because they had not sufficient shells. The enemy had in that matter stolen a march upon them and had during the winter, when military activity is at its minimum, rapidly produced large supplies of high-explosive shells.