bad conditions. In the field of the telescope some mark is arranged to indicate the point to be brought on to the target in taking aim. The most usual form is a vertical and horizontal cross wire, across the diam. of the field, though in some cases arrows or circles are used. In telescopes intended for use at night, small electric lamps are fitted for illuminating the cross wires so that they and the target are shown up on a dark background. All telescopes are arranged so that they are not affected by the recoil of the gun and are placed as close as possible to the trunnions of the gun, or cradle, so that the motion of the gunlayer's head is limited although the gun may be moved through large angles of elevation.
In turrets the sight brackets are usually bolted directly on to the trunnions of the slide and rock with it, so that all backlash is elimi- nated. The sight bracket carries an arc upon which the telescope- carrier travels, and the position of the carrier on the arc determines the angle between the axis of the telescope and that of the bore of the gun. This angle is expressed in yd. on a dial which is geared to 3. rack on the arc of the sight bracket. The lateral motion for adjusting deflection is given to the telescope by pivoting its carrier at the front end of the bracket, and moving the rear end by gearing which is attached to the deflection dial. The whole of the deflection-setting gear is arranged to move in elevation with the telescope-carrier. Means are provided for adjusting the sight for the M.V. of the gun and for the temperature of the charge. This is usually effected by moving the zero position of the setting pointer of the sight.
At all hand-worked guns (except the smallest) 2 sights are fitted, one on the right and the other on the left of the gun. One of these sights, usually the left one, is used by the gunlayer, who fires the gun, for laying the gun in elevation, whilst the other is used by the trainer, whose duty it is to keep the vertical cross wire trained on the target. The two sights are cross-connected so that both can be set simul- taneously for the range and deflection adjustments. The sights are mounted as close to the trunnions as possible to avoid undue motion of the heads of the gunlayer and trainer. In the most modern sights the telescope-carrier travels on an arc in much the same way as has been described for turret sights, but some types of sight are still in existence in which the front end of the carrier is pivoted and the rear end is given a vertical motion by suitable gearing.
A more complicated type of sight is needed for use with high- angle guns against aircraft. The target in this case is moving in 3 planes; that is, horizontally and laterally for range and deflection, and also vertically, this latter being usually described as the vertical deflection. The great speeds at which aircraft move in these 3 planes render the design of an accurate and easily set sight a difficult matter. During the war a number of high-angle sights were produced, most of them being of a makeshift character adapted for use with con- verted mountings. The problem of obtaining accurate gunfire at aircraft from guns mounted on the unstable platforms afforded by ships still remains to be solved, and the type of sight which will be adopted for this purpose still awaits the result of further inves- tigation. Meanwhile many devices are in use for applying the range and the vertical as well as the horizontal deflection, but none of them can be said, up to the present, to meet all the con- ditions required.
Director sights are of the same general type as those of the guns that they are designed to fire, but there are additional devices fitted to compensate for various errors introduced by the distance of the master sight from the guns and to suit the details of the director mounting itself.
The electrical " follow the pointer " system of transmitting ranges and deflections to the guns, which is in general use and has been previously referred to, adds complications to the details of the design of the sights, but does not affect the principles.
Naval Howitzers and Bomblhrowers. A new class of naval ordnance was introduced in the latter part of the World War for use against submarines. This was the naval howitzer or. more particularly, bombthrower.
The early submarines were small in size, had little or no gun- power and were liable to damage by gunfire when on the surface. Consequently the first anti-submarine measures took the form of arming vessels with small guns. This had the effect of forcing the submarine to dive when within range of an armed vessel, and thus their movements were handicapped and successful torpedo attack was made more difficult. The submarine rapidly in- creased in size and commenced to carry larger guns, thus becom- ing much more formidable when on the surface. This led to the mounting of anti-submarine guns of larger calibre, but the sub- marine at all times offers a small and difficult target. Also, all but the very earliest boats are built with double hulls and 'are consequently very difficult to damage seriously by direct attack with the gun, owing to the " pressure " or inner hull being below the waterline.
From early days it had been realized that some form of under- water attack would be called for to counter the submarine and
as early as 1912 attempts were made to produce a diving shell. Extensive trials were carried out without success with the object of obtaining a projectile that would dive at low angles of descent when fired from a high-velocity gun with a flat trajectory.
Howitzers and bombthrowers were first tried during the investigation of the diving-shell problem in 1912, but the ranges obtained were considered, at that time, to be too small to be of value at sea. The question of the use of howitzers was reviewed at the outbreak of war, but the development of the submarine at that time was not such as to demand this form of weapon as a necessary counter-measure. It was not until after the pronounced increase in the size of the submarines in the latter part of 1916, that the question was seriously consid- ered. It was at this time that the Sutton-Armstrong3-5-in., 200- Ib. stick bombthrower was developed as the first purely naval weapon of this type. The early part of 1917 produced an urgent demand for a simple form of howitzer for use afloat, to fire a shell or bomb which would dive and which could be rapidly man- ufactured in large numbers. This led to the introduction of the S-in. howitzer, the 7-S-in. bombthrower, the 7'5-in. howitzer, the lo-in. bombthrower and the i i-in. howitzer, and at the same time experimental work was carried out with several naval weapons proposed by various inventors. The final develop- ment in the use of these weapons was their adaptation to fire the heavy external stickbomb, of the same type as that used in the3'5-in. S.B.T. This greatly increased their effectiveness as anti-submarine weapons, and the use of these projectiles from all howitzers and bombthrowers was being extended when hostilities ceased.
The 3-5-in. Sutton- Armstrong stick bombthrower was evolved from a model already in existence which had been designed for trench war- fare. The bombthrower consists of a single tube with a trunnion ring screwed on to it. The tube screws into a spherical explosion chamber on which is a lateral extension carrying a simple swinging breech mechanism. To facilitate manufacture an improved design was introduced at a subsequent date, in which the spherical ex- plosion chamber was replaced by a cylindrical one with an axial, instead of a lateral, breech mechanism. The original bombthrower was fitted with a Temple silencer, with a view to preventing flash and noise when in the trenches. This being of no importance in naval conditions, the silencer was removed, but it had to be replaced by a " blast cone " and a " blast screen " was embodied in the design of the mounting, as without these accessories the gunlayer's seat was untenable owing to muzzle blast.
The bombthrower is carried in a revolving bracket which is mounted on a fixed pedestal. The extreme elevation obtainable is 55 and the low limit in the earlier mountings is 18, but this was afterwards altered to 5 degrees. A simple aperture sight is carried on a bracket bolted to the right trunnion and the bombthrower is elevated by the usual rack-and-pinion gear worked by a hand-wheel. A downward blow of some 80 tons results from firing the bomb- thrower on this rigid non-recoil mounting, and the strain caused damage to the base plates and ship's structures when the bomb- throwers were first mounted. This defect was remedied by increasing the base plate to 60 in. sq., thus distributing the blow on firing over a greater area.
The charge is contained in a small brass cartridge cylinder fitted with a percussion primer. The bomb when loaded rests in the blast cone at the muzzle. The stick occupies practically the whole length of the tube of the bombthrower, and is fitted at its lower end with a gas check. The accuracy of the bombthrower is excellent, a mean error of 30 yd. being obtained at 45 elevation and of only 20 yd. at 30 elevation. When the development of the submarine campaign called for a larger bursting charge in the bomb, a 35O-lb. bomb was supplied for this bombthrower, which was fired with the same charge as the 2OO-lb. bomb. The accuracy with this heavy bomb is extraordinary, mean errors of 7 yd. at 45 elevation and of 19 yd. at 30 having been observed. A considerable number of these bomb- throwers were mounted in small craft during the war, and they proved to be one of the most efficient of the anti-submarine weapons of this type employed.
The 5-in. breechloading howitzer was a small single-tube breech- loading howitzer, designed for army use by the Elswick Ordnance Co., and adapted for use afloat. Their 50 and 4O-lb. projectiles were too small for anti-submarine purposes, and the few of them that were mounted afloat were eventually withdrawn. Nevertheless they were the first weapons of the howitzer type that were actually mounted afloat for anti-submarine purposes.
Early in 1917 the necessity arose for a howitzer or bombthrower, for use afloat, which could be produced rapidly in large numbers and which was simple to handle and capable of a rapid rate of fire. The design chosen, from amongst others, was that of Messrs. Vickers for
