Fire Control Fundamentals

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Fire Control Fundamentals, NAVPERS 91900, 1953, was created to introduce sailors to thebasics of weapons fire control. The basic fire control principles of gun against a surface target arethen applied to the control of Antiaircraft guns, Antisubmarine Weapons, Torpedoes, Rockets andGuided Missiles.

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Trainee Knowledge Level:

The knowledge level required for proper

understanding of "Fire Control Fundamentals"and its application to Navy equipment is that of atrainee who has mastered the following subjects:

"Basic Electricity""Basic Electronics""FT Rating Indoctrination"

SECTION 50

RATING SPECIALIZATION INSTRUCTION SHEETS

"FIRE CONTROL FUNDAMENTALS"

TABLE OF CONTENTS

PART A - THE STORY OF FIRE CONTROL

PART B - GUNS AND INTERIOR BALLISTICS

PART C - THE PROJECTILE IN FLIGHT - EXTERIOR BALLISTICS

PART D - HITTING A MOVING TARGET FROM A MOVING SHIP

PART E - AN INTRODUCTION TO FIRE CONTROL EQUIPMENT OPERATION

PART F - A TYPICAL MAIN BATTERY SYSTEM

PART G - TYPICAL ANTIAIRCRAFT FIRE CONTROL SYSTEMS

PART H - INTRODUCTION TO ANTISUBMARINE FIRE CONTROL

PART I - INTRODUCTION TO TORPEDO FIRE CONTROL

PART J - INTRODUCTION TO ROCKET AND GUIDED MISSILE FIRE CONTROL

PART K - HOW YOU WILL LEARN ABOUT FIRE CONTROL EQUIPMENT

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A-1

THE STORY OF FIRE CONTROL

Introduction

The purpose of this series of instruction sheets is to introduce you to some of the many things youwill encounter in your work as a Fire Control Technician. You will get an overall view of the historyof fire control and a brief summary of its present-day applications. You will see how the basic firecontrol principles, developed for firing a gun at a surface target are applied to the control ofantiaircraft guns, antisubmarine weapons, torpedoes, rockets and guided missiles.

You will learn what the major; components of various modern fire control systems are and whatfunction each serves. As you learn more about fire control, you will realize that the Navy is only asstrong as its fire power, and in order for that fire power to be effective, it must be accuratelycontrolled. That's where you-as a Fire Control Technician-play a vital part in making your ship aneffective weapon against enemy ships, planes and submarines. It will be your job to operate andmaintain the many complex devices used in your ship's various fire control systems.

A-2


Your Job as a Fire Control Technician

After you learn the theory of fire control, you will not automatically become a proficient fire controltechnician. Your duties as a fire control technician will be many and varied. You will be called uponto operate and maintain many different kinds of mechanical and electrical devices. You must be amechanic and know how to use hand tools, gages and instruments effectively to adjust and repairmechanical fire control devices. You must also be an electrician, for you'll be working withelectronic circuits, electric motors, and switchboards. Your battle station may be at a gun directortracking the target, in the plotting room operating various computing devices, or operating a radarset to determine target range and accuracy of fire. Whatever or wherever your station, you mustknow how to operate and maintain your equipment.

You have been selected to study fire control because the Navy believes you have the many variedqualities necessary to become a fire control technician. Now let's go on and learn more about thechallenging and vital problem of controlling the Navy's fire power-fire control!

A-3


The Story of Gunpowder and Early Guns

Gunpowder, first developed by the Chinese many centuries ago, was not used for anything butentertainment (fireworks) for a long time after its discovery. The discovery of the principle of thegun-that is, using an explosion to fire a projectile from a tube-was made accidentally in the thirteenthcentury by a man who was trying to turn mercury into gold. According to the story he added aningredient which caused his mixture to explode, blowing the top off his kettle. Repeating theexperiment several times gave him the idea for a weapon which became known as a "gun." Fromsuch a humble beginning developed the intricate and powerful weapons of today which certainlyaren't for "entertainment."

Early guns were very crude and unpredictable, often more dangerous to the gunner than the enemy.For many years arrows and spears were more effective than guns in combat. A crossbow boltcould penetrate a knight's armor; the early guns couldn't. The archer could fire several arrows whilethe gunner was loading and firing a single round.

Many improvements in firearms were required before guns became a useful weapon. Stoneprojectiles were replaced by those made of bronze and then lead and iron balls in the fourteenthcentury, and as time went on gunpowder and guns were also improved to the point where gunnerybecame an important art.

A-4


The Story of Gunpowder and Early Guns (continued)

Guns were used on ships on a large scale for the first time in the fifteenth century, when a Spanishfleet opened fire with cannon at point-blank range on the Turkish fleet, which was quickly defeated.Subsequent sea and land battles involving firearms began to prove the effectiveness of guns ifproperly used in combination with other weapons. By the middle of the sixteenth century guns ofmany sizes and kinds were being used, some of them 10 feet long, capable of firing a 4-1/2 inch ironshot 500 feet per second for a distance of 2000 yards. These were soon exceeded by aMohammedan cannon which fired a 400-pound projectile more than two miles. Gunnery wasbeginning to come into its own!

Less than 200 years ago, naval guns were fired at point-blank range; gunnery was still an art, not ascience, and fire control was largely a matter of skillful seamanship in maneuvering the ship intoposition to enable the gunners to hit the target. The range and destructive power of guns continuedto increase over the years, from an average effective range of 100 yards in the mid-1800's to morethan 40,000 yards today. Methods of fire control in the modern sense were not developed until thenineteenth and twentieth centuries. You will trace the development of gun sighting systems and firecontrol devices on the next few sheets.

A-5


The Development of Gun Sighting Systems

The first concern of a fire control system is to provide an effective way of aiming. This is the functionof the gun sights. Prior to 1800, there was no need for elaborate gun sighting systems, because theguns themselves were inaccurate except at close range. Guns were simply pointed at the target byeye.

Gun sights introduced early in the nineteenth century consisted of fixed front and rear sights mountedso that the line of sight across their tips was parallel to the bore of the gun. Toward the end of thenineteenth century, a sight telescope was developed by a Navy Lieutenant. It consisted of a simpletelescope containing a pair of crosshairs, and was mounted in such a way that the line of sight couldbe moved with respect to the axis of the gun to correct for some of the factors which affect thesolution of the fire control problem. Present-day gun sights take many forms, but they still performthe basic function of all gun sights-to provide a horizontal and vertical offset between the line of sightand the axis of the gun bore in order that the target may be kept in sight while the gun is aimed sothat the fired projectile will hit the target.

A-6


Early Fire Control Developments

Improvements in gun sighting systems alone, however, were not enough, as the range and intricacyof guns increased. It became necessary to develop other fire control instruments which couldaccurately and rapidly solve the fire control problem. The first of such devices was the stadimeter,an optical device used to measure range, which enabled the gunner to determine range moreaccurately than could be done by eye. The stadimeter was crude and good only for short ranges,but embodied a principle later used in the rangefinder.

The largest and most important corrections in fire control are to compensate for the relative motionbetween gun and target. In the old days the positions of gun and the target at the moment of impactof projectile were predicted by eye. In the early 1900's an improvement was brought about bymarking the position of the target on paper as it moved along its course (by measuring distance anddirection from ship to target) from which it was possible to determine the approximate course and

future position of the target. This let to the development of the rangekeeper, a device whichautomatically corrects for changes in target range. The range-keeper was refined and improved till itreached its present form, making possible the rapid solution of other factors in the fire controlproblem.

A-7


Early Fire Control Developments (continued)

Another factor which had to be taken into consideration to obtain accurate fire was the inclination ofthe gun caused by the roll and pitch of the ship's deck. One early device used by nautical gunnerswas a round shot suspended from a spar. The gunner watched this improvised pendulum and firedhis piece just before it was parallel to the mast (when the deck was horizontal). This same principlewas later incorporated in the "stable element" and the "stable vertical." These devices act like achild's spinning top, in that their axes always remain truly vertical, thus establishing a reference planefrom which gun elevation angles can be measured.

A final factor which had to be considered to provide an effective fire control system was accuratedetermination of where each shot fell. In the early days each gun crew worked out its own sightsettings and the gun was fired as soon as that gun crew had corrected the aim of their particularpiece. With all guns firing independently it was impossible to spot the individual gun's effectivenesswith any accuracy. The central control station, from which all guns were controlled, was developedto correct this inaccuracy. A new instrument called a "director" was installed in the control station.

At first the director was a pair of "master" gun sights, from which settings were transmitted to theguns. As time went on, the gun director became more complicated and performed more jobs, whichyou will learn about a little later

A-8


The Major Components of a Modern Fire Control System

On the three previous sheets you learned about the early development of gun sighting systems andfire control devices, and why it was necessary to develop certain pieces of equipment to performspecific tasks. The illustration on this sheet shows a typical modern fire control system and its majorcomponents. It is not necessary at this time for you to learn the details of how and why all of thecomponents function. Your job now is simply to become generally familiar with what the majorcomponents are, their primary function and how they are related.

A-9


The Function of Fire Control System Components

The principal components of a fire control system, as shown on the preceding sheet, are the gundirector, the rangekeeper (or computer), the stable vertical (or stable element) and the gun turrets,as well as related auxiliary equipment (ship's gyro, pitometer log, communication systems, etc).

The gun director is located high in the ship's superstructure to provide as distant a horizon aspossible. By means of optical equipment and/or radar (an electronic device which you will studylater, used to locate objects by means of reflected radio waves), the director is able to track thetarget and measure its range, bearing (direction from ship to target), course and speed. It transmitsthis information to the rangekeeper and stable vertical, which are located in the plotting room belowdecks. The rangekeeper takes the information from the director, combines it with information onown ship's course (from the ship's gyroscope) and speed (supplied by the pitometer log), andcontinuously computes the predicted target position. It then transmits orders to the gun turrets,which are equipped with automatic equipment to train and elevate the guns in accordance with theorders received from the rangekeeper. The stable vertical measures the inclination of the deck andsupplies this information to the director and rangekeeper which incorporate the necessarycorrections in their computations.

The complexity and arrangement of the components of fire control systems will vary widelydepending upon the ship, its armament, whether the system controls main, secondary or antiaircraftbatteries, how many guns are controlled, and other factors. Basically, however, the major elementsalways serve the same function-the director sights and tracks the target, the rangekeeper (computer)

calculates the required gun settings and the turrets aim the guns. Remember this and you'll be well onyour way to understanding fire control.

A-10


A Survey of Modern Surface Fire Control Systems

A surface fire control system, as the name implies, is designed to control the fire of guns usedagainst surface targets-that is, enemy ships or shore installations. Of course, the surface fire controlsystem of a battleship is much more complex than that of a destroyer. Now let's take a look at sometypical surface fire control systems as found on various types of ships.

A battleship is equipped with two main battery directors and two plotting rooms-one of eachlocated forward and one aft. Either director together with the equipment in either plotting room canbe used to control all or part of the main battery. In addition, equipment in each main battery turretpermits emergency individual control of the guns.

Secondary batteries on a battleship consist of 5-inch dual purpose guns used against aircraft as wellas surface targets. There are four secondary battery directors, any one of which can be used tocontrol one or all of these guns. They can also be used, if necessary, to control the main battery.The two secondary battery plotting rooms are similar to the main battery plotting rooms, in that eachcontains two rangekeepers (computers), two stable elements and the necessary auxiliary equipment.

A-11


A Survey of Modern Surface Fire Control Systems (continued)

Cruisers have fire control installations similar to those of battleships, except that there are only twodirectors for the dual purpose secondary battery.

On a destroyer, the main battery is also the dual purpose battery, and consists of a number of 5-inch guns. There is only one main battery director and one plotting room, which control all guns. Ason the larger ships, provision is made for individual control of each turret in the event that thedirector is damaged or destroyed by enemy action.

Because of the greater complexity and flexibility of the armament on a battleship, it is apparent that amore complex fire control system is required.

Naval ships are armed with weapons other than those designed for use against surface targets. Onthe following sheets you will learn something about the fire control systems used to controlantiaircraft, and antisubmarine weapons, torpedoes and guided missiles.

A-12


Antiaircraft Fire Control Systems

Antiaircraft fire control systems of various types are designed to control guns ranging in size fromlight machine guns through 6-inch dual purpose.

Battleships and heavy cruisers are equipped with secondary batteries consisting of dual purposeguns, which are used against aircraft as well as surface targets. The main battery on a destroyerconsists of a number of 5-inch dual purpose guns. The fire control systems used with these weaponsfor surface fire also control them when they are used against enemy aircraft. These guns are used forlong range fire at high or distant air targets, and are centrally controlled as explained on the twopreceding sheets.

The other antiaircraft guns carried by Navy ships are 3-inch, 40-mm and 20-mm automatic guns.The number and arrangement of these guns depends on the type of ship carrying them. The 3-inchand 40-mm guns-called the "heavy machine-gun battery"-are equipped with a separate director andfire control system. Decentralized control permits firing at many targets at once; however, in anemergency cross connections permit the heavy machine-gun directors to control the dual purposeguns and vice versa.

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

A-13


Antiaircraft Fire Control Systems (continued)

There are two general classes of antiaircraft fire control systems: (1) "linear-rate systems" whichdetermine changes in target position, course and speed by measuring the distance betweensuccessive target positions; and (2) "relative-rate systems" which measure the angular velocity of theline of sight to determine target motion. The theory of operation of these two systems will beexplained later.

The linear-rate system is used as the primary means for control of 5-inch dual purpose guns for bothsurface and antiaircraft fire. The relative-rate system of fire control was developed during WorldWar II when increased speeds made it necessary to reduce the time required for solution of theproblem of hitting aircraft, since this time is limited by the relatively short range of machine guns.Although originally used only for light machine guns (20-mm), systems of this type have beendesigned to control 40-mm, 3-inch and 5-inch guns.

A-14


The Antisubmarine Attack Problem

The primary weapons used by surface vessels against submarines are torpedoes, depth charges andahead-thrown missiles. Depth charges are either rolled off the stern of the attacking ship orprojected a small distance to the side, while ahead-thrown missiles are projected to a position(controllable within narrow limits) ahead of the attacking ship. Torpedoes may be fired to the side,ahead or behind the attacking ship (within certain limits), and continue on a set course under theirown power. The fire control problem is thus largely a tactical one, since it is necessary to solve theproblem of maneuvering the ship into attack position.

When depth charges are used, the attack position is ahead of the submarine to allow for the sinkingtime of the charges. For ahead-thrown missiles and torpedoes it is not necessary for the ship to passahead of the submarine, since the missiles are aimed to fall at the indicated target position. In eithercase, however, it is necessary to determine (1) the course along which the attacking ship must besteered, and (2) the time to fire, so that the depth charges or missiles will arrive at the predictedtarget position at the same time as the submarine.

A-15


A Survey of Antisubmarine Fire Control Systems

Before an attack can be made on an enemy target-whether it is on the surface, in the air orunderwater-the attacking ship must locate the target and determine its bearing, range, course andspeed. For surface and air targets this information is obtained by means of the gun director andrangefinder as previously discussed. Underwater targets cannot be detected with this equipment,however, since they are not visible and radar is useless underwater. Submerged vessels aredetected by "sonar" which uses reflected sound waves instead of radio waves as in radar to detectand determine underwater target range and bearings.

A sound wave generator, called a sonar transducer, is located below the waterline of the attackingship. It transmits sound waves which reflect back to the ship after hitting an underwater object. Bymeasuring the time required for the sound waves to reach the target and return, it is possible todetermine the range; bearing is the direction from which the waves were reflected. Target courseand speed can be calculated by observing changes in range and bearing.

Once the above factors are known, it is necessary to determine own ship's course and the propertime for firing, as opposed to gun elevation and train orders required for surface or antiaircraft firecontrol.

A-16


A Survey of Antisubmarine Fire Control Systems (continued)

The antisubmarine fire control system on board the general purpose destroyer (the most commonnon-specialized submarine fighter) normally consists of the following units: (1) the sonar equipment,which transmits and receives the sound waves to locate the target; (2) the sonar range recorder,

which automatically records the range received from the sonar equipment, and passes thisinformation on to (3) the attack director, which also receives target bearing information from thesonar, ship's bearing from the gyro and ship's speed from the pitometer log. The attack director'sjob is to solve the fire control problem-that is, determine ship's attack course and time to fire.

The attack plotter displays on a screen a picture of the movement of own ship and target, and maybe used to solve the fire control problem graphically in case of failure of the attack director.

You will learn more about these components and their operation a little later.

A-17


A Survey of Torpedo Fire Control Systems

The torpedo is recognized as the most effective underwater weapon of naval warfare; it may be ofthe "homing" or "non-homing" type. Our discussion here will pertain only to the non-homing type.Torpedoes may be fired from submarines, aircraft or surface vessels, for each of which the torpedofire control problem is quite different. When firing torpedoes from aircraft, submarines or PT boats,it is necessary to have the ship pointed at least in the general direction of the target. A destroyer,however, is equipped with torpedo tubes which can be trained to aim at the target.

Two kinds of control are used for destroyer torpedo fire: (1) "bridge control, " the primary methodof control on modern destroyers, which is remote control from directors; and (2) "local control, " inwhich the proper settings are made at each mount by means of the torpedo tube mount sight, whenthe director control system is inoperative. The primary function of the torpedo director is to controlthe tube mounts by electrically indicating to them the proper settings to obtain the desired torpedocourse for scoring a hit.

Destroyers usually fire their torpedoes in a "spread," to increase the chances of scoring a hit on anenemy who is probably aware that he is being attacked and is therefore taking evasive action. Youwill learn more about the use and control of torpedoes later on.

A-18


A Survey of Rocket and Guided Missile Fire Control Methods

Short range barrage rockets have proved to be effective weapons in shore bombardments. Theprincipal ship used to fire rockets is the LSMR, which mounts ten rocket launcher assemblies. Anyone or all of these launchers may be controlled by either of two duplicate rocket fire controlsystems. Each system includes a gun director, a stable element, a gun order corrector and auxiliarycomponents, all of which were developed for the control of conventional guns, but have beensuccessfully converted to the control of rocket launchers.

The conventional projectile fired from a gun, or the barrage rocket, is committed to a given courseat the time of firing. The target may change course or speed during the time of the projectile's flight,in which case the result is a miss. A guided missile, however, is subject to control so that it will altercourse after launching in order to score a hit regardless of the target's evasive tactics! In order to

control such a missile it is necessary to know the relative positions of missile and target at all times,and to be able to effect appropriate alterations to the missile's course from a remote position. Toaccomplish this, guided missile fire control systems include components carried by the missile whichreceive and carry out directions received from radar and computing equipment on the ground.

A-19


How You Are Going to Learn the Fundamentals of Fire Control

On the preceding sheets you read about the history of guns and fire control devices, you learnedabout the main components of a fire control system, and you took a quick look at some of itsspecialized applications in antiaircraft, antisubmarine, torpedo, and rocket and guided missile firecontrol systems. In continuing your study of fire control fundamentals you will learn about the theoryof guns and ballistics-what happens to a projectile while in the gun and during flight. Then you willgo deeper into the basic fire control problem-that of hitting a moving target from a moving ship. Youwill learn more about the various components of a fire control system, how they perform their jobs,and their application in surface, antiaircraft, antisubmarine, torpedo, rocket and guided missile firecontrol systems. Finally, you will be given an introduction to some of the Navy's special equipmentused in fire control devices, including radar, sonar, synchros and servos.

You will learn about these things by studying these information instruction sheets and discussingwhat you read with your instructor and your classmates. You will be given plenty of opportunity toask questions and make comments about what you read. If something is not clear to you, ask aboutit, because there is much to be learned, and it is important that you fully understand each lessonbefore proceeding to the next.

Now that you know what and how you are going to study, let's get started by reading about gunsand interior ballistics.

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