U. S. NAVAL INSTITUTE, ANNAPOLIS, MD.

TELESCOPIC SIGHTS FOR GUNS.

BY LIEUTENANT JOSEPH STRAUSS, U. S. NAVY.

When one considers the accuracy with which modern guns are constructed, the careful inspection and proof of the ammunition, and the ease with which the weapon is manipulated, he is naturally led to expect the best results in target practice. An examination of the target sheets is somewhat disappointing. We know that the gun used can put all of its shots within a three or four-foot circle at a thousand yards, that the men are carefully drilled at aiming and pointing, and we are then compelled to examine the third element in the problem of hitting the target, that is, the means we have provided for actually sighting the gun.

With the ordinary bar sights now in use the gun captain is called upon to see three objects in line, viz., the rear sight, 15 inches distant; the front sight, 50 inches distant; and the target, anywhere from a few hundred to several thousand yards away. To see three, or even two, objects distinctly at such widely varying ranges is an impossibility. The eye without conscious effort will accommodate itself to any distance, but it can only focus for one distance at a time. This can easily be shown by looking through a wire screen held a foot or two from the eye at some object several hundred yards away. The distant object will be distinctly seen, and the wires of the screen will be scarcely visible; and conversely, if we see the screen the distant object will only give a hazy impression. In sighting a gun, then, there must be a compromise effort to see all three objects at once, with the result that they are all indistinct, making the pointing largely a

line of sight and the axis of the bore should be exactly what the sight bar calls for and totally independent of the personality of the gun captain.

Lack of acuteness of vision also militates against good practice with the ordinary bar sight. The front sight being a cone or point, and the rear sight a notch, the front sight would probably appear shorter and the notch less deep to poor eyesight than to good, again bringing in the personal element to the detriment of the gun practice.

It was not until 1801 that sights of any kind were used in aiming guns. Up to that time the men were instructed to look along the line of metal," or exterior of the gun, and aim at some point of the enemy's ship above the point to be hit. When first introduced, both front and rear sights were fixed and merely gave a line parallel to the bore. This innovation took place nearly 500 years after the introduction of cannon, and was objected to then by as good a man as Lord Nelson. It was not until much later when a French army officer succeeded in introducing movable rear sights graduated to cable-lengths.

Until the beginning of this century it would perhaps have been superfluous to have introduced accurate sighting methods when the gun element had contributed so little to accuracy. The charge was measured out, and if the powder was a little old, a quart or so more was used. Guns were single shotted or double shotted with little thought of the effect on the trajectory. However, the optical defects of bar sights must have been apparent at an early date, for as long ago as 1857, Capt. Younghusband, of the British Army, introduced the telescope as a means of sighting guns. The telescope was mounted on a bar secured to one of the trunnions of the gun and parallel with its axis.

The telescope sight came into more extended use in 1875, when Major Scott, of the British Army, introduced his sight. The telescope is attached to the gun until it is laid, and is removed just before the gun is fired. Its distinguishing feature is an arrangement by which it can be attached to or removed from the gun quickly. It is still issued to the English Army with their 12-pdr. field guns.

About eight years ago Captain Grenfell, of the British Navy, produced an arrangement by which the telescope was mounted

nions of the gun. As the sight bar is raised the telescope is depressed through a corresponding angle equal to the required range, after which the gun is elevated until the optical axis is coincident with the target. This telescope is trained and elevated with the gun.

In 1890, Lieut. Fiske, U. S. Navy, obtained a patent on a telescope sight which had the distinguishing feature of being secured to the shield of the gun, and which depended, more or less, on the roll of the ship to bring the line of sight in coincidence with the target. This arrangement avoided all shocks to the telescope and permitted the gun captain to keep his eye at the sight while actually firing the gun.

The introduction of gun mounts in which the gun recoils in a slide or sleeve in the line of fire solved the difficulty hitherto present in all attempts at sighting guns on shipboard by means of telescopes. This permits us to mount the telescope to all intents and purposes on the gun. The eye can remain at the sight while the gun is recoiling, and all shocks to the telescope are avoided; the gun can be elevated and depressed without disturbing the setting of the telescope, yet the latter partakes of all the movements of the gun except recoil.

The Bureau of Ordnance design includes an ordinary terrestrial telescope fitted with cross-wires, having its optical axis parallel with that of the gun and arranged to oscillate in a vertical plane, or rather a plane making a small angle (equal to the drift angle) with a vertical plane through the axis of the gun, by means of a screw pressing against a rigid arm depending from the barrel of the telescope. Attached to this screw is a drum, upon the periphery of which are marked the ranges. As the drum is revolved to the higher range the screw moves back and allows the front of the telescope to depress. The optical axis is then made the line of sight by elevating the gun (and with it of course the telescope) until the target appears in the cross-wires, when the gun is fired. In the case of turret guns the sight is mounted on an oscillating table, which is made to move parallel with the gun by means of a straight rod, the lower end of which is attached to the slide on which the gun recoils, the upper end being attached to the table. This device produces a simple parallel motion between the telescope and gun, and is in effect the same

the smaller guns. It is inadmissible to mount it directly on the slide when the gun is in a turret, for the reason that at low ranges with the ship heeled, or when firing at elevated objects, too large an opening would be required in the turret for sighting through. Fig. I explains this.

FIG. I.

Fig. 2 shows the method of applying the sight to a turret gun. ON is the arm on the oscillating slide. B is a rod connecting the arm ON to an arm of equal length keyed to a cross-shaft, to which the telescope table E is also keyed. Upon this table rests the telescope stand, so arranged that it can be moved in azimuth by means of the tangent screw t. It can also be adjusted in angular altitude by means of the screw a. After getting the telescope adjusted these screws are not disturbed until something has occurred to destroy the parallelism of gun and telescope. The rod B is provided with a turnbuckle, so that its length may be adjusted to equal the distance between the center of the trunnion of the gun-slide and the center of the cross-shaft. Fig. 3 shows the telescope as designed for mounting on other than turret guns, the only difference being in the base of the stand. In this case the stand is stepped into a circular socket and clamped by means of a cam. By this means it may be readily shipped and unshipped. A is the securing screw for the diaphragm carrying the cross-wires. BB are the front and rear finder sights. C is the stand. D, arm cast in one with the trunnion band, and is provided with a hardened steel piece E

secured by means of the tension spring F. G is a drum made of aluminum upon which the ranges are marked. It is turned by means of the milled head H until the proper range comes next to the pointer J. The marks are arranged spirally about the drum, and the pointer is so shaped as to hide all adjacent marks.

The pointer is secured to the stand by the screws KK; the slots at these points permit of a small movement of the pointer, so that in adjusting the sight in altitude it is only necessary to bring its optical axis parallel to the gun, after which the pointer can