| NAVAL ORDNANCE AND GUNNERY, VOLUME 1 CHAPTER 8 SEMIAUTOMATIC WEAPONS |
| HOME INDEX Chapter 8 Semiautomatic Weapons A. General B. Five-inch 38-caliber assemblies C. Five-inch 54-caliber assembly |
| A. General 8A1. Introduction Semiautomatic guns are case guns in which energy stored during recoil is used on counterrecoil to operate the breech mechanism, eject the empty case, and later to close the breech and (if required) cock the firing mechanism. Power for loading, ramming, and firing is supplied separately and requires independent control by members of the gun crew. The cycle of operation is as follows: (1) the gun recoils after firing, and energy is stored in the counter-recoil system; (2) during counterrecoil the breech-block is automatically lowered and the empty case is extracted; (3) after the next case is rammed into the chamber, the block is automatically raised to close the breech; and (4) the firing mechanism is cocked, either when the block is lowered or when it is raised, depending on the design of the gun, and the gun is then ready for another operating cycle. The firing rate of semiautomatic guns depends largely upon the time required to load. All semiautomatic guns use fixed or semifixed ammunition, depending upon their size. These guns utilize a sliding-wedge breechblock. A firing mechanism is fitted in the breechblock to fire the primer electrically or by percussion. Semiautomatic guns are used extensively by the United States Navy on all types of combatant and auxiliary vessels. Examples of this type of gun are the 5”/38 (all types) and 5”/54 (Mark 39 only) designed for semifixed ammunition, and the 3”/50 and 5”/25 which use fixed ammunition. Although these guns differ in mechanical details, they all use the vertical sliding-wedge semiautomatic breech mechanism. The 3”/50 caliber semiautomatic gun is a pedestal-mounted, hand-loaded weapon which is not capable of firing at a rate comparable to the newer 3”/50 caliber rapid-fire gun, which is covered in chapter 9. The former is still in use on certain types of small patrol craft and on auxiliary vessels. The 5”/25 caliber gun is also used on an open-pedestal type single mount. The dual-purpose 5”/25 caliber is now mounted only on a few of the older heavy cruisers in the reserve fleet. During World War II a special wet-type 5”/25 caliber pedestal mount was developed for use on fleet submarines. This is a single-purpose mount with maximum elevation of 40 degrees. It is not equipped with a power drive. The ammunition is fixed, consisting of a projectile weighing 54 pounds and a cartridge with a loaded weight of 21 pounds. The 5”/38 caliber and the 5”/54 caliber assemblies are in more general use than any of the above and will be described in more detail. The 5”/38 caliber is particularly well adapted to use for the purpose of demonstrating the operating principles generally applicable to all semiautomatic guns. |