THE MANY USES OF

Evening Post, Volume CXXIX, Issue 111, 11 May 1940, Page 18

THE MANY USES OF

THE effect of artillery fire can be illustrated by explaining something of the mechanism of guns, writes Captain M. M. Corpening in the "Chicago Tribune." Guns are of two types: quick-firing (Q.F.) and breech-loading (8.L.). The underlying principle of Q.F. is the mechanical absorption of the recoil by means, of brakes, buffers, or recuperators. The absorption of recoil permits of a higher rate of fire, since ■ the gun does not have to be run up and relaid after each shot. All guns must have provision to move laterally (traverse); vertically (elevation), in order to obtain the j elevation required for any particular range, and axially during recoil. A gun is cradled on slides so that it may recoil and be returned to. the firing position under control of the recoil, system. Muzzle velocity depends on the pressure developed during the projectile's passage down the bore, the distance through which this pressure acts, and the frictional resistance encountered by the projectile. In modern guns the maximum pressure rarely exceeds 22 tons per square inch. A single shot fired from a 75 m.m. gun corresponds to 750,000 horse-power, worked up within 0.0006 of a second. At the time of discharge a temperature two arid a half times higher than that at which steel melts is created within the gun bore. The energy thus. released* propels the shell. Fired from a modern piece, a shell will attain a velocity of 2700 feet during the first second of its flight. The bore of all guns is rifled to impart a spin to the projectile as it travels along the spiral .grooves. This permits use of an elongated shell j and insures accuracy by flight point first. The shape of the head is designed to reduce air resistance, thereby increasing range. The life of a gun depends on the rate of erosion in the bore in relation to rounds fired. As the time down the bore is only a fraction of a second, the actual working life of a heavy gun that could fire 300 shots is only a few seconds.

Propelling charges are of smokeless powder, which leaves no thick clouds of smoke lingering over the gun to obscure the target. In the smaller calibre, 37 m.m. to 4.7 in, the charge is contained in the cartridge case. This is known as "fixed ammunition."

Semi-fixed ammunition, in which the cartridge case' is not crimped to the base of" the projectile, is used with

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howitzers, where the powder charge is in the form of zoned bags within the cartridge case, and where it is necessary to adjust the weight of the charge for various ranges.

In the larger calibre of guns, where the projectile is heavy, it would be impractical to use a complete round, so the propelling charge and primer are issued separately.

In loading the larger guns the projectile is .first rammed to its seat, and the propelling charge then inserted. It is contained in one or more bags for ease in handling, since a 16in gun, for example, would require a charge weighing as much as 8001b.

The primer for guns of such heavy natures is a small brass cap loaded with' a charge of black powder. It has in its head a percussion cap which is struck by the firing pin of the gun, thus igniting the black powder charge, which in turn ignites the propelling charge. In small calibres the primer is assembled in the head of the < irtridge case, but with large calibres it is assembled in the breech mechanism of the gun. The size of the primer increases with the calibre of the gun. In a 16in gun an igniter of 61b may be used. .

Shells are made in sizes from slightly over one inch in diameter,- weighing one pound, to 16 inches in diameter, weighing more than a ton, while for some superheavy pieces they are of even larger order.

An artillery shell carries with it an immense force, components of which are its weight, reaching up to 1£ tons; its staggering initial speed, and the terrific po.wer of its explosive contents, which may amount to as much as 660 pounds. The heaviest constructions and the thickest armour cannot sustain the shock of such projectiles, and when lesser shells are employed the loss in power is made up for by rapid firing.

The wide variety of shells—grenades, shrapnel, armour piercing, concrete piercing, incendiary gas, and smoke shells —illustrate the wide diversity in the use of artillery.

High explosive shells, fired by all natures of guns as well as howitzers, are used against troops in the open and for covering and harassing fire. They are further employed for wire cutting, for engaging troops under light cover, and against tanks. Equipped with graze and delayed action fuses, they can be used against troops in trenches and. for the destruction of buildings and other • strong points. With time fuses, they are used against

hostile aircraft. The explosives employed are T.N.T., picric acid, ammonium picrate, and amatol.

Shrapnel is used against troops in the open, for offensive and protective covering fire, and for general harassing. A shrapnel shell is filled with balls and is regulated by a time fuse consisting of eithsr a powder train or mechanical adjustment. When the time fuse functions, the powder charge is exploded, and the balls expelled outward in the shape of a cone, with action similar to that of a shotgun. The

This projectile is used by coast artillery. The bourelet is a portion of the surface of the cartridge which touches the bore of the .gun lightly, preventing wobbling as the projectile passes through the barrel. The projectile is exploded by a delayed fuse upon impact. The use of soft steel in the base is necessary to prevent the projectile from hanging on armour plate.