CHAPTER-15-B

NAVAL ORDNANCE AND GUNNERY
VOLUME 2, FIRE CONTROL

CHAPTER 15
INTRODUCTION TO FIRE CONTROL

INDEX
INTRODUCTION TO FIRE CONTROL
A. Historical Preface
B. Modern Fire Control Systems

B. Modern Fire Control Systems

15B1. Batteries

For a long period, the batteries of a single ship frequently consisted of guns of various sizes. Because of the difficulty of controlling and spotting the fire of so many batteries, the practice of using guns of the same size and ballistic characteristics in a given battery was adopted. This practice also resulted in a simplified system of supply for ammunition and replacement parts.

The size and number of guns in a battery depends upon the type of ship. Batteries are generally referred to as:

Main battery. The guns of the largest caliber aboard a ship. The term is sometimes extended to indicate the weapon of greatest potential effect. For example, the main battery of an aircraft carrier is its planes; of a submarine, its torpedoes; of certain landing craft, the rocket battery.

Dual-purpose battery. Guns which are adaptable for use against either aircraft or surface targets. In ships which have a single-purpose main battery, the dual-purpose battery may be called the secondary battery. Many other ships have a dual-purpose main battery.

Machine-gun battery. Permanently emplaced automatic weapons of all calibers, used chiefly against aircraft.

Some typical examples of combatant ship gun batteries are shown in Figures 15B1 and 15B2.

15B2. Fire control systems

The exact composition and arrangement of a ships fire control system depends upon such factors as the type of ship and the size, number, purpose, and effective range of its guns. In general, fire control systems have the following characteristics:

1. The primary method of fire is director fire. When the number and arrangement of guns in a battery permits, the battery may be controlled from one station, or the fire may be divided and controlled from several points against multiple targets.

2. Provision is made for observations to establish present target position and to spot the fall of shot.

3. Computers figure the predicted position of the target, the ballistic corrections, and corrections to compensate for roll and pitch of the ship. These data are used to compute gun orders in train and elevation which are transmitted to the guns.
4. Gun orders keep the guns constantly positioned in space, ready to fire whenever the firing key is closed.

5. Provision is made for stand-by methods of control if the primary method is inoperative.

6. Efficient communications are provided, with duplicate systems for transmitting information.

7. Provision is made for control of the battery at night, including the control of star shells and searchlights.

15B3. Battleship systems

On a modern battleship, the two primary main-battery directors are the highest on the ship, the forward one being about 120 feet above the waterline, the after one about 75 feet. Either director, together with equipment in the plotting rooms, can control all or part of the main battery. Also, any one of the four secondary-battery directors can be used to control all or part of the main battery. In addition, equipment in each turret permits individual, but less effective, control of the turrets independently of the directors and plotting rooms. Five optical rangefinders, one in each main-battery director and in each turret,* provide main-battery ranges. Fire control radars in the fire control tower and in each main-battery director provide radar range (and bearing) for the main battery.

Below the waterline are the forward and after plotting rooms, each of which contains rangekeepers, stable verticals, graphic rangekeeping devices, switchboards, and other instruments. Information is received in plot from the radars, rangefinders, and directors, and is combined with other information obtained from various sources. Computed quantities are transmitted to the guns for their control. Either plotting room may control any part of the battery. Auxiliary computing equipment is provided in each of the three turrets, so that each may fire independently.

The secondary battery has four directors, each of which has its own rangefinder and radar, and may control all or any part of the dual-purpose battery. There are two secondary (dual-purpose) battery plotting rooms similar to those of the main battery, except that they contain no graphic plotting devices. Each is equipped with two computers, two stable elements, the necessary indicating instruments, and switching equipment. With director. controlled fire it is possible to engage four secondary battery targets simultaneously with independent illumination control.

The heavy machine-gun battery is equipped with a separate director and fire control system for each of its mounts. Many of the directors are equipped with radar. Decentralized control permits firing at many targets at once, and facilitates target acquisition. Flexibility of control is provided by cross connections permitting the heavy machine-gun directors to control the adjacent dual-purpose mounts, and the secondary-battery directors to control the heavy machine-gun mounts.

The light machine guns (20-mm) are equipped with individual lead-computing sights.

15B4. Cruiser and destroyer systems

Cruisers have fire control installations similar to those of battleships, except that there are only two directors for the dual-purpose battery (i.e., the secondary battery on cruisers with turrets; the main battery on AA cruisers). Figure 15B1shows the fire control installations on a guided missile cruiser,

NOTE: Radar has replaced the optical rangefinders in the turrets of some of the later cruisers.

U.S.S. Boston (CAG-l). On guided missile cruisers of this class, the after 8-inch triple turret and the after 5-inch twin gun mount have been replaced by two twin Terrier missile launchers.

Destroyers have only one director and one plotting room for the dual-purpose (main) battery. The control of dual-purpose and machine-gun batteries on cruisers and destroyers is similar to that on battleships, but they can engage a smaller number of targets simultaneously, because of the smaller number of guns and directors.

15B5. The fire control problem

The principal subject of the next several chapters is the fire control problem. This term has come to mean the entire series of measurements and computations used in the control of weapons, beginning with the designation of the target and the type of fire, and ending with the destruction of the target. For all batteries, the problem of gun fire control is solved in five steps:

1. Establishing the present position of the target. The first step in the solution of the problem is to establish the present position of the target with relation to the ship by measuring its range, bearing, and, for air targets, elevation.

2. Computing lead angles. Lead angles in elevation (called sight angle) and in bearing (called sight deflection) are computed to allow for wind, gun ballistics, and relative motion of own ship and target during the time of flight of the projectile. This is the principal function of all rangekeepers and computers.

3. Correcting for motion of gun platform. Corrections are computed to counteract the effect of the constant rolling and pitching of the ship.

4. Making up gun orders. Since the guns are so mounted that they can move only in train and elevation, all the foregoing information is converted into gun positioning orders, and is constantly corrected, so that the guns are continuously positioned for firing.

5 Correcting fall of shot. In case of inaccuracy of computation, the projectiles may fail to hit the target. Errors are determined by observation and are corrected by the application of corrections known as spots.

15B6. Presentation of the fire control problem

The fundamental considerations in the solution of the fire control problem are the same for both surface and air targets. Since the surface problem is less complicated, it is considered in this text before the air problem.

It should be clearly understood that the emphasis in this text is upon principles, rather than upon details of specific installations. Descriptions of specific equipment are limited to the most commonly used examples of each type. Further information is to be found in the publications of the Bureau of Ordnance.

Methods of use are subject to change; consequently, this publication describes procedures only as illustrations of the capabilities of the equipment. The practicing gunnery officer is referred to fleet publications of most recent date for guidance in this respect.

It is emphasized that the student is expected to receive only an introduction to fire control in this text. The expert gunnery officer is made by constant experience and by the detailed study of all fire control gear with which he is associated, particularly that on his own ship.

15B7. Symbols and definitions

Fire control has developed its own language, and the study of the subject requires familiarity with the definitions and symbols of which this language is composed. Gunnery definitions, as standardized by the Fleet Training and Readiness Branch of the Office of the Chief of Naval Operations may be found in appendix E. They are adequate for general use, but their application varies somewhat among different fire control systems. The Bureau of Ordnance has established standard fire control and torpedo control symbols of a more restricted nature, the most useful of which are to be found in appendix F. Fire control symbols and nomenclature, as used in the sections of this book not limited to specific equipment, have been prepared to agree with the most recent current practice. It should be noted that symbols and nomenclature are subject to modification for individual equipments, and that all symbols, nomenclature, and definitions are subject to change by the Bureau of Ordnance and the Chief of Naval Operations. Throughout this text, symbols and definitions occur as required by the subject matter. In some cases the standard definitions have been paraphrased to make them easier to understand.