US Naval Fire Control, 1918 (original) (raw)

US Naval Fire Control, 1918

Byron Angel (byron@trident-usa.com) has extracted the chapter on Fire Control from Elementary Naval Ordnance and Gunnery, by Lieutenant H. C. Ramsey USN (Boston: Little, Brown and Co.), 1918. Byron comments

The book appears to reflect an earlier period. The author's foreword is dated 1 June 1918, so he could not possibly have taken advantage of any of the lessons learned through the 6th BS's North Sea service with the Grand Fleet. As a matter of fact, some of the stuff seems pretty archaic, such as single shot ranging and range-taking by one rangefinder only. There are also some really fascinating comments that merit further discussion IMHO. For example, the author claims that the newer warships were NOT being equipped with range and deflection clocks and that such devices were going out of use. What is this about? Is it possible that the new Ford FC computers coming into service had these clock functions built in and thus made separate devices superfluous? This claim alone begs further exploration.

Fire Control

Let us consider the fire-control system for the main battery only of a large ship

RANGE-FINDER GROUP

The range-finder gives us, fairly accurately, the distance of the enemy ship at the instant of observation, the reading on the range-finder being direct in yards.

In the newest ships, the range-finder mechanism is mounted in the turrets themselves, the lense being located in arms which project a short distance sideways, one from each side of the front of the turret. In the older type of battleships, having two turrets, one forward and one aft, a range-finder is mounted on the tope of each turret.

The range-finder group consists of an officer and several men, well-trained in the practical use of the instrument and having especially keen eyesight.

When an enemy ship is first sighted, they take station at the most reliable range-finder on the ship and use this. In the event of casualty to it they either shift to another instrument, or the work is taken up by another crew stationed at the other range-finder.

When the enemy ship is forst sighted, and at the direction ofthe fire-control officer, a range-finder reading is taken to determine her distance, and the time noted by stop-watch. Also the bearing of the enemy vessel is taken at the same instant, with a contrivance called a "bearing-indicator". At intervals of 30 seconds from the first range and bearing, and from each other, take a series of ranges and bearings. By plotting each consecutive range and bearing at the proper time interval distance from each other, you can establish on a chart a series of fixes, or positions of the enemy ship at various short intervals. A line drawn carefully through these fixes will give the course of the enemy, and from it you can also determine his rate of speed. This is designated as the "determination of the course and speed of the enemy".

The actual determination of this course and speed is worked out in a station below decks, called the plotting-room, the ranges and bearings and the time intervals being communicated to the plotting-room by the range-finder group. As soon as the course and speed is found accurately, it is transmitted to the fire-control officer in order that he may make such calculations as are necessary to determine the initial (gun) range and deflection at which to open fire, allowing for all conditions at the time that are other than standard.

FIRE-CONTROL STATION

This is the station in battle of the "chief fire-control officer", who is also the "gunnery officer" of the ship. From this station he controls and directs the firing of all the guns of the ship, designating the poijnt of aim of the guns, either all on one target, or on several targets, as necessity dictates. He give the electric firing signals from this station, by what is known as the master-switch, operating all firing signals in the ship.

The fire-control station on the newest ships is located directly over the conning tower, which is the battle-station of the commanding officer of the ship. On other ships it is located at the base of the foremast, on the bridge, or on the upper bridge, when there is one.

The essential requirement is that the "fire-control station" must be in direct communication with the conning tower, which we call "ship control station". It is perfectly evident that the best results will be obtained only by the coordination of the ship and fire-control.

The commanding officer, in "ship control", is also immediately advised of the speed and course of the enemy as soon as this is determined. If the ship is operating singly, the commanding officer after a study of the situation will advise the fire control officer when to open fire, and how.

The command might be given in this manner: "Open fire at the enemy ship when she bears North-East and is distant 12,000 yards, using your 12-inch guns in salvo".

The fire-control officer will immediately calculate the initial range and deflection to be set on sight-bar and azimuth drum, making allowances for all conditions other than standard at the time, and for known errors of individual guns. These calculations will be made by the solution of problems similar to that covered in "Elementary Gunnery", or, in modern ships, they can be made with the aid of certain ingenious mechanical and electrical contrivances.

The initial range and deflection, as soon as determined, is communicated to the "plotting room". Here it is immediately plotted on charts with relation to the course and speed of the enemy. From the plotting room the range and deflection is sent to each gun and turret, an dthe sights are set accordingly. The range and deflection is sent to the guns by three different methods to avoid any possibility of confusion: by telephone, by voice tube, and by "visual" indicator. Each turret or gun reports back "set" as soon as the sights are ready.

The fire control officer, after receiving the report, "set", watches closely the enemy shipWhen she isnearly on the predetermined line of bearing, by operation of his master switch, he causes the "buzzer" to sound in each turret or at each gun. At the instant the enemy ship is on the line of bearing, in this case north-east, he causes the "bell" to ring at each gun or in each turret.The buzzer signal means "stand by to fire". The bell signal means "fire". There is usually an interval of about five seconds between the two signals.

The exact instant of sounding the bell firing signal must be carefull judged by the fire-control officer, not only as regards the bearing of the enemy ship at the instant, but also as regards the motion of the ship. Range and deflection are both greatly affected by undue motion of the firing vessel: pitching and rolling. The signal should be given at such a time as the ship is steady longest in one position, such as the top or bottom of the roll.

At the firing signal, all guns fire in salvo or together, unless certain one have been previously designated not to fire.

Each turret, battery, or group of guns is usually fitted with a "relay switch" on the firing signal system. If for any reason certain guns are not to fire on the signal, by pulling this relay switch, the turet or battery officer cuts out the bell and buzzer at the particular turret or group of guns.

RANGING SHOTS

The foregoing has been based on all guns of the ship being fired together, or in salvo, at initial range and deflection. When the initial range an ddeflection can be determined with any degree of accuracy, the first salvo may strike and demoralize the enemy, and an important advantage to be scored.

On the other hand, if it is impossible to determine the inital range and deflection with any degree of accuracy, ranging shots are resorted to. Instead of firing together, the guns of a broadside are designated to fire singly, and in succession, at certain intervals. By means of "spotters" we judges the landing place of each shell with reference to the enemy ship and correct the next range and deflection until the target is "found". Then take up firing in salvo.

COLLECTIVE SHIP CONTROL

The method of opening fire covered in the foregoing has presumed the ship to be acting singly, under the control of its own commanding officer. In a modern engagement, there is no doubt but that the single ships would be under the control of a flag officer having station on the flag ship of the division, fleet, battleship force, etc.

In this case directions for opening fire would come from the flag ship, as would also direction for continuing it. The interior system of fire-control would, however, be the same as has been outlined.

SPOTTER'S GROUP

Our range-finders and other mechanical and electrical instruments would be ideal for giving us at any instant the exact range, course, and speed, etc., of the enemy if could compensate also for the various errors of gun-fire with which we have to contend.

Certain of these errors of gun-fire are variable and indeterminate in an exact sense, and for this reason we are compelled to resort to individual spotting, or judging of the landing place of each shell or salvo of shells fired.

Spotters for long-range firing are stationed usually in the "tops" of the cage masts, the aim being to give them the advantage of the most elevated position in the ship. An officer especially trained in "spotting" is stationed in each top, and is designated Spot #1 and Spot #2, respectively, for fore and main-masts. Each spotting officer has with him several men stationed at voice tubes and telephones to plotting-room, fire-control, etc. In action, with all guns firing at one target, Spot #1 does all the spotting. In case of casualty to him, Spot #2 continues. Where the fire of a ship is divided on two targets, each spotter controls one group of guns.

The duties of a spotter are to keep a constant, close watch on the target or enemy ship, and by various methods to judge as accurately as possible the point of fall of a single shell, or the mean point of fall of a salvo of shells with reference to the objective. A quick determination is made of the change in range and deflection necessary to make the next shot or salvo score a hit, assuming of course that both firing and target ships remained in the same position, without advancing, until the next salvo could be fired.

Immediately after each shot or salvo, the spotter telephones to the plotting room the result of his spot, giving the corrections in range and deflection direct.

Of course, both vessels are moving and so change their relative positions, so that the "spots" cannot be placed directly on range scales an dazimuth drums. The range and deflection must be further corrected for the position of both ships, their courses and speeds, at the instant of firing. This is done in the plotting room.

PLOTTING-ROOM CREW

The plotting-room in located in the interior of the ship, usually below the protective deck. As a rule it is well forward. In some of the newer ships it is below the protective deck and practically under the conning tower and the fire-control station.

A switchboard in the plotting room gives telephone connections to every fire-control group on the ship, to spotters, turrets, guns, etc.

The principal duties of the plotting-room group are to plot on charts or on plotting boards, or to represent graphically with reference to the plane of fire, the course and speed of the target, and the rate of change of range and deflection, so that at any instant we can determine from reference to the charts the range and deflection at the instant, and also the the continuous rate at which the range and deflection are changing at that particular time.

Separate plotting boards are provided; one for the determination of "range" and the other for "deflection". The initial range and deflection and the course and speed of the enemy ship are plotted on the charts at the beginning of an engagement, the range and deflection being sent out to the sight-setters, and "set" being reported to the fire-control station.

The spotter "spots" the first salvo and gives a correction, such as: Up 100, Right 2. This correction is immediately plotted on range and deflection boards, and the proper range and deflection for firing the next salvo is obtained, taking into consideration the course and speed of both firing and target ships. The new range and deflection is now sent to the sight-setters who correct their settings as ordered. "Set" is reported to fire control and at the proper moment the firing buzzer and bell are sounded.

The spotter estimates the mean point of fall of this second salvo, and gives correction again to plotting room, and the procedure is repeated.

When a sufficient number of "spots" have been obtained and the range is increasing or decreasing at a rate that can be determined, a line or curve representing the "rate of change of range" is plotted. "Deflection" may be handled somewhat similarly. At any instant, knowing the approximate rate of speed of the enemy ship, you may determine his rate of speed amde good on a course parallel to your own, as was done in computing original range and deflection. This, with the bearing of the enemy, gives "deflection" at the instant.

In cases where a salvo hits or straddles the target and the spotter does not desire to change either range or deflection, he reports to plotting room "No change". This is reported in turn to the fire-control officer by the plotting room.

RANGE CLOCKS

These are mechanical contrivances or clocks that are used in determining continuously ranges and deflections at which to set the sights in firing on an enemy ship. Certain data is placed on the clock, such as the rate of change of range and deflection, as soon as this is determined on the plotting boards. The clock gives, at any instant for this rate of change, the range and deflection to set on the sight-scales. "Spot" corrections may be placed directly on the clocks.

These clocks are little used at the present time, and ships are no longer being fitted with them.

CONTROL OF BROADSIDE BATTERY

The latest idea in the control of broadside batteries is that the officer in charge of the broadside, or of a certain group of guns in the broadside, not only completely controls the fire of these guns, but is himself the spotter for them also. In his spotting position he has a "relay or group control switch". When this switch is in, he receives the fire-control signals and fires with other guns or groups on the ship. When he is not ready to fire, he throws out his switch and no signal sounds for his battery. He has with him a man with a range and deflection board, who plots all "spots" and sends out range and deflection after each salvo.

This system is largely used for torpedo-defense purposes.

SUB-FIRE-CONTROL STATIONS

Where a ship is equipped with both 12-inch and 8-inch guns in turrets, and also comparatively heavy caliber, 6- or 7-inch broadside guns, it is possible that all calibers might be desired to be brought into action together.

In such a case, we employ sub-fire-control stations.

A sub is provided for each caliber gun - they are called Sub-12; Sub-8; and Sub-7, depending on the caliber of the gun, and each sub-station has the particular duty ofaiding in the control of the fire from its own guns.

Each sub sends out ranges and deflections to its own guns and reports "set" for that caliber to fire-control. In some cases, each sub has its own "deflection" and "rate of change of range" boards; also range clocks; and each works with the plotting-room to control in the simplest way the entire firing of the ship.

Spotting

Spotting, as here used, refers to the judging of the point of fall of a projectile, with reference to a target or an enemy ship, in order to determine if a hit has been made, and, if not, to estimate what changes in range and deflection are necessary to make the next shot score a hit.

This is a subject which can and will be discussed only in the briefest and most general way, due to the desire of the Navy Department to keep the details of all methods employed and the results of all experiments conducted along these lines confined to confidential publications issued to officers of the Service.

The range-finder method of determining the range of an enemy vessel, in combination with other mechanically and electrically operated fire-control instruments, it is fully recognized, would be ideal for giving us at any instant the exact range, course, and speed of the enemy, were it not for the various and numerous "errors of gun-fire" with which we have to contend.

Certain of these errors of gun-fire are variable, and cannot be exactly determined, and for this reason we are compelled to resort to individual spotting, in combination with our range-finder and other instruments, in order to maintain an accurate control of the fire.

Spotters should be officers, highly and especially trained for this particular duty. Thei importance cannot be over-stimated.

For long range firing, 6000 yards or over, the spotters are stationed in the highest available part of the ship, usually in each "top" of the cage or fire-control masts. Large and comparatively powerful spotting telescopes are located in each "top", and the spotter stations himself at this.

When spotting for smaller caliber guns and sometimes under special conditions, a lower elevation is sometimes more advantageous and a special "low spotting position" is provided lower down in the cage mast.

After a shot has been fired, the spotter keeps the target or enemy ship closely in his field of view, and noted where the projectile lands with reference to the objective. By constant practice and with the aid of certain data he is able to judge in an almost inappreciably short time the change in range and deflection necessary to bring the next shot on the target.

There are two principal methods of spotting -- the direct flight and the splash method.

The DIRECT FLIGHT METHOD is used for short ranges only, and requires the actual observance of the projectile itself as it falls in, or passes through, the plane of the target or enemy ship. As the projectile passes through the field of view of your telescope, which has been kept on the target continuously since the shot was fired, it appears as a comparatively small, blurred, and rapidly moving spot.

When the projectile can be spotted in this fashion, it is not difficult to tell if a hit was made, and if not, to give the necessary correction.

The other method of spotting, used for long ranges, is called the "VERTICAL SPLASH METHOD". Spotting by this method requires a well-trained spotter. Briefly, the method is to observe the splash caused by the fall of the projectile, and from the position of the splash to judge the point in the water, beyond, in front, or to the right or left of the target, where the projectile fell. By projecting the line of vision from the spotter�s position, through the base of the splash, and also, in the same straight line, through the vertical plane of the target (actual or extended), you can judge at what point the projectile, either in the air or in the water, passed by or through the vertical plane of the target, by reference to a previously prepared "splash diagram". The corrections to the plotting room are given direct in yards of range and divisions of deflection.

Example -- Up 200, Right 4.

SPLASH DIAGRAMS are used to assist the spotter. These represent graphically, on a target or ship drawn to a small scale, the area on the water within which the projectile would have to fall in order to hit the target (the danger space). This danger space or parallelogram drawn in on the vertical plane of the target represents the space within which the projectile must appear to the spotter to have passed, if it hit the target. Range and deflection lines are also drawn around the small scale target, giving the corrections necessary to bring the projectile on the target on the next shot. These diagrams should be drawn up before a target practice. Tables contain data to be used in connection with the diagrams.

The correction to be of value must be accurately and quickly determined, and this requires in a spotter a keen sense of judgement and a quick mind.

SPOTTING SALVOS: Modern battle practice, we know, is more a matter of salvos of shots than single shots. Our spotters, then, must be especially trained in spotting salvos.

There is always more or less dispersion or spreading of shots in salvo firing, due to the individual errors of guns and to personal errors of pointing. These can hardly be avoided.

In spotting salvos with a wide dispersion of fire the spotter has a difficult task. He must first determine the mean point of fall of all shots, and then determine the correction for the amount in range and deflection necessary to bring this mean point on the target on the next salvo. In salvo firing the shots should "straddle" the target, half over, and half in front.

Single-shot spotting, as compared with salvo spotting, is a very simple proposition.

SPOTTING BOARDS AND RANGES

These are merely arrangements to represent on a small scale, reduced in proportion, the problem of the spotter. By using a miniature target, and miniature splashes, it is possible to have a fairly realistic and certainly a very beneficial "spotting drill".

GENERAL

In any spotting it is better to spot "under" than "over". You are more likely to hit her somewhere with a low shot than with a high one.

Excessive or radical spotting corrections should be avoided. If a shell hits somewhere, even though not right on the "bull", it is usually best to leave well enough alone and give no correction.

Last Updated: 6 October, 2002.

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