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 | 921k | Pictured on the left are quads and 20mm's practice firing aboard South Dakota (BB-57) in 1943 in the Atlantic. A GUN is a mechanical device, consisting of a tube closed at one end and at the moment of firing, capable of containing a projectile and a propellant charge, and of so controlling the explosion of the charge as to discharge the projectile with a high velocity. A RIFLE is a gun whose bore has cut in its surface a number of spiral grooves, into which the soft metal of the rotating band on the projectile is forced, thus imparting to the projectile a motion of rotation. The raised portion between the grooves are called the lands. A BUILT-UP GUN is any gun made up of different parts, the idea being to get an assemblage of parts best able to resist the pressure of the powder gas. The gun may be built up of different metals. The most usual forms are; (1) The built up gun with initial bore compression obtained by shrinkage, the exterior parts being heated to go over the interior parts, and (2) the "wire wound" gun. A RADIAL EXPANSION MONOBLOC GUN is a gun composed of a single forging. In this gun the initial bore compression is obtained by the application of hydraulic pressure to the interior of the gun tube. It may be constructed with or without a separate liner. Larger radially expanded guns, however, are not necessarily monobloc (one piece). A LOW POWER GUN is a gun having a low muzzle velocity and a low pressure. A HIGH POWER GUN is a gun having a high muzzle velocity and a high pressure. BAG GUNS are guns which do not use metallic cases for the powder. A mushroom and gas-check pad are therefore required to prevent the powder gases, under the high pressures of explosion, from escaping to the rear around the plug. CASE GUNS-guns in which a metallic powder case is used, this case preventing the escape of gas to the rear. Therefore, a mushroom and gas check pad are required. AUTOMATIC GUNS are guns in which the force of the explosion is used to eject the fired cartridge case and load another cartridge. When ammunition is properly supplied, no force but pressure on the trigger is required for continuous fire. SEMI-AUTOMATIC GUNS are those in which the force of explosion ejects the fired cartridge case and leaves the breech so that it closes automatically when another cartridge is inserted. Machine guns are small caliber automatic guns. PARTS OF A GUN Exterior Parts The BREECH is the rear end of a gun, the muzzle is the front end. The rear cylinder, at the rear end of the gun is that part over the chamber where the metal is thickest. The slide cylinder is that part of a gun forward of the rear cylinder which fits in the slide and moves through it in recoil. The CHASE is the sloping portion, forward of the slide cylinder, extending up to the muzzle. The NECK is just to the rear of the muzzle, where the chase reaches its smallest diameter. The trunnions are two horizontal cylindrical projections at right angles to the bore axis, the purpose of which are to support the gun on the carriage. They are located at or near the center of gravity of the gun, and form the axis about which the gun moves in elevation. INTERIOR PARTS The BORE of the tube is that part of the interior of the tube that is of uniform diameter from the powder chamber to the muzzle. The CHAMBER of a gun is that space at the breech and allotted to the powder charge. The CALIBER is the diameter of the bore, measured in inches to the tops of the lands. The caliber, as defined above, is used as a unit in expressing the length of a gun. For instance a 5 inch, 38 caliber gun would be a gun whose bore is 5 inches in diameter and 38 calibers long, or 38 times 5, equals 190 inches. NAVAL GUN MOUNTS The MOUNT is the entire system interposed between the structure of the ship and the gun itself. The principal functions which the mount must perform are; (1) support the gun in such a position that it can readily he used, (2) provide for elevation and train and (3) provide for recoil and counter-recoil. The SLIDE is a cylindrical casting within the gun slides axially in recoil and counter-recoil. In elevation, the slide, with its contained gun, operate independently with the rest of the mount. From either side of the slide, in a horizontal plane, project the trunnions, which rest in suitable bearings in the carriage. The CARRIAGE is the part which rotates in train, carrying with it the slide and the gun. The carriage rests upon and rotates on a roller on a stationary member called: The STAND which is bolted to the ship's structure. TYPES OF ANTI-AIRCRAFT GUNS The defense of surface craft against air attacks accomplished by two types of batteries: (1) Heavy anti-aircraft guns-3" or 5" guns, firing combination time-fuzed and base-detonating ammunition at comparatively long ranges, and (2) Rapid fire guns-20mm, 1.1" or 40mm machine guns firing impact-fuzed projectiles to short ranges at a very high rate of fire. (There are also .30 and .50 caliber machine guns which fire common or armor piercing projectiles.) To be adequately defended against attacks by heavy, high altitude bombers, dive bombers, torpedo planes, and strafing planes, or any combination of these, a ship must be equipped with as many as possible of both the above types of guns. In the design of an anti-aircraft gun the following features are striven for: (1) High gun elevation. (2) Low trunnion height. (3) Ease and rapidity of gun laying. (4) High muzzle velocity. (5) Flat trajectory. (6) Long life. (7) Large caliber. It is seen immediately that no gun can embody all these features at once. For example, high elevation and low trunnion height are in direct opposition to each other, as are high muzzle velocity and long life. Therefore, every A.A. gun is a compromise, with the most desirable features for any special purpose given preference. The 5"/38 gun, for instance, was designed to fulfill the need for a double purpose (surface and A.A.) gun of larger caliber, long range and fairly high rate of fire. On the other hand the 40mm and 20mm machine guns were designed for use against aerial targets at short ranges, and at an extremely high rate of fire. | Text submitted by Pieter Bakels. | |
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