Sights

In this type the dial sight is connected to a toothed arc which gears with an elevation indicator on the oscillating bracket. The arc is slightly tilted with respect to the sight to compensate for drift as elevation is applied. The dial sight carries an adjustable bubble, by means of which the angle of sight is applied, and also a bubble for cross-levelling the sight.

Sights for Fixed Artillery (Coast Defence).

In fixed coast defence mountings the design of sights is simplified by the following facts:— ( i ) The mounting has been made level and therefore no method control post by means of position-finding instruments (see article RANGE-FINDERS) and is in most respects similar to central fire control methods used in battleships.

With the lighter natures of coast artillery, the role of which is to deal with fast-moving torpedo craft, rapidity of fire is essen tial and the layer should be able to lay and control his gun with as much ease as a rifleman does his weapon. This can be affected by means of the automatic sight which makes use of the fact, stated above, that for each gun the angle of sight determines the range and therefore it is possible so to interconnect gun and sight that when the sight is pointing at the target, the gun has the correct line and elevation. Fig. 8 shows the general arrangement of an automatic sight.

Sights for Anti-Aircraft Artillery.

When firing at air craft, it becomes necessary to ensure not only that the trajectory passes through the target, but also that the shell wiil burst at that point. Time-fuzes are used for bursting the shell and the problem of laying now is to give correct line, elevation and fuze length. Further, the high speeds of modern aircraft make travel deflections no longer minor corrections and, as the target now moves at considerable and varying heights above the gun, change of angle of sight has also to be taken into account. Thus in this branch of artillery work sights will have to be designed so as to permit of two types of deflection—vertical deflection, due to change in angle of sight and lateral deflection, due to travel of target across the front of the gun. The laying arrangements will,

in addition, have to provide some interconnection between fuze and elevation used.

The methods of laying fall into two divisions:— ( i ) Control from a central post.

(2) Laying at the gun.

Control from a Central Post corresponds to central control in battleship. Some predicting instrument observes the tar get, selects some point on its course, predicts the time it will arrive there, passes the necessary quadrant elevation, bearing, and fuze to the gun which is laid by indicator just as in the correspond ing case in coast defence—in this case no sight arrangements other than the indicators are necessary.

In laying at the gun sights of the oscillating type are used. Angle of sight is obtained by direct observation of the target. Predicting instruments give the necessary deflections which are put on the sights, the sights being kept pointed at the target; this results in the gun being laid on the position at which the target is to be hit, known as the future position. The fuze having been ordered the layer now gives tangent elevation to the gun till a pointer cuts the corresponding fuze-line on a dial geared to the elevating mechanism. The gun is now at the correct tangent elevation. The process is continuous as the angle of sight is constantly changing and the layer for elevation has to keep on altering his elevation so as to keep the pointer on the fuze line corresponding to the fuze loaded in the gun. Rifles and Machine Guns.—The sights used for this class of weapon vary very little throughout the world. Except for special purposes, telescopic sights are not used. The type is the tangent sight, consisting of a fixed fore-sight near the muzzle and a hind sight (notch or aperture) movable in a vertical plane usually by swinging about a horizontal axis fixed transversely to the barrel. This swinging leaf takes the place of the tangent scale in fig. 2.