Page 229 - NAVAL SCIENCE 3 TEXTBOOK

IfJ Naval Guns

Almost all naval ships and many kinds of naval aircraft are fit-
ted with various kinds of gUllS. GUllS may be llsed "gainsl surface,
shore, and air targets. Ship gUlls designed for engaging both air
and surface targets are termed dl/al-plIrpose systems. Most gUlls in
lise today are alltomatic; that is, the recoil orthe gun ejects the fired
powder case and reloads the gUll.

Gun Nomenclature
A gllll is basically a tube or barrel closed at one end, from which a
projectile is ejected at a high speed b), gases produced by a burning
propellant. The inside or bore of the barrel is rijbf with groo\'es
having a right-hand twist of uniform din meter from one end to
the other. Ritling callses the projectile to spin in flight. which keeps Guns like this 25-mm chain gun comprise the secondary batteries
the projectile from tumbling after it leaves the barrel, thus provid- aboard ships like the guided missile destroyer USS Mason (DOG 87),
ing greater accuracy and range. monitoring a vessel captured by pirates off Somalia late in 2008.
(Michael McCormick)
The size of naval guns is expressed in one of several ways.
I nside or bore diameter, measured from the tops of the rifling lnnds
(high side of the rining grooves), may be specified in millimeters diameter, howevcr, the diameter is specified in either miHimeters or
(111m) or, for older guns, in inches. For gUlls less than 3 inches ill inches. and the length in calibers. Caliber for these gUlls is defined
bore diameter, their barrel width is often referred to as their mliiJer, ns a number equal to the length of the gun in inches divided by the
expressed in millimeters or decimal fractions of all inch. A 20-cali- diameter of the gun in inches. For example, a gun having a bore
ber machine gun, for instance, is a machine gun whose bore diam- diameter of 3 inches and a barrel 150 inches long is designated
eter is 20 millimeters. i\ 32-caliber revolver is a handgun whose 3-inch, 50-caliber. Similarly, a 5-inch-diameter gun 270 inches in
bore diameter is .32 inches. For guns larger than 3 inches in bore length is called" 5-inch/54-caliber gun.
The nrc of elcmlioll is the total vertical arc through which a
gun barrel can be raised and lowered. The nrc of tmin is the total
horizontal arc through which a gun mount mily be rotated. If a
gun were mounted well forward on the bow, it could have a clear
Line reference field of Are up to about 320 degrees, but a gun mounted aft might
marks
have only a lSD-degree arc astern. Electrical and ll1eclwnical wt-
Ol/t cal11S are incorporated in gun circuits and on mounts, which
prevent guns li'om being fired when they are pointed at a part of a
ship or aircraft's structure.
Liner
The 11I01l11t, or glllll/lOlI/ lt, is the entire structure between the
gun nnd the ship or aircraft's structure. It supports and secures the
gun, and provides for the gun's elevation, train, and recoil.
A bnller), of guns is a group of gun mounts of the same size,
normally controlled ti'om the same point. The main battcq' of a
ship consists of the Inrgcst size gUlls on board. The secondary bat-
teq' consists of dual-purpose guns, or guns of the next smaller size.
Diagram of the barrel of a rifled gun, showing lands and grooves.

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