|NAVAL ORDNANCE AND GUNNERY
VOLUME 2, FIRE CONTROL
NAVAL GUNFIRE SUPPORT
B. Naval Gunfire Support Operations
22B1. Selection of the weapon
Selection of the gun or weapon to be used in naval gunfire support is determined by the nature and size of the target
to be engaged and by the proximity of friendly troops to the target. The 5-inch gun is normally used for close
supporting fire; its rapid rate of fire and relatively small pattern size make it an excellent weapon for neutralization and
destruction of targets immediately in front of advancing troops. Destroyers are usually assigned close supporting-fire
duties because their maneuverability permits them to shift positions easily and quickly and to take positions close
inshore for direct fire on targets in coastal areas.
Guns of 8-inch and larger caliber, with their great accuracy at long range, are normally reserved for deep supporting
fire. The lethal bursting radii of projectiles from these guns limit their employment in close support. Moreover, ships
mounting these guns (battleships and cruisers) are hampered in responding quickly to fire commands because they are
less maneuverable than destroyers and their fire control organization is more complex. The larger ships also have to
carry out a number of additional duties. The destructive power of the projectiles of large-caliber guns makes them
particularly effective against heavy installations ashore.
The 6-inch gun has qualities suitable for either close or deep support, but the light cruisers mounting these guns are
better adapted for deep support use, since their maneuverability is restricted.
The 3-inch and 5-inch guns of DE's, APD's, DM's, and DMS's are suitable for harassing fire missions
of the sort often executed against areas remote from our own troops, such as towns, harbors, and coastal air strips.
The use of these ships for this purpose provide a necessary feature of support and releases ships with more accurate
fire control equipment for use where precision fire is required.
40-mm guns are effective for area neutralization where heavier caliber guns are not required. The fire control
installation used with these guns is inadequate for indirect fire or safe close supporting fire. These guns are particularly
effective against shoreline targets, especially enemy personnel in caves. When such fire is controlled by the dual-
purpose gun directors, it is accurate and effective at short ranges; when not so controlled, larger safety limits with
respect to proximity of own troops must be allowed.
22B2. Specialized fire-support ships
The support of troops in landing operations has brought forth many new special weapons and specialized fire-support
craft. The most important among these are:
1. The LSMR. This is primarily a rocket ship; its main armament consists of launchers for 5-inch spin-stabilized
rockets, the maximum range of which is about 11,000 yards. This craft can be used for deep support, harassing, and
neutralization fire as well as for beach neutralization. Because it is equipped with a rocket fire control installation, it
can use its fire somewhat closer to own troops than the rocket LCS, which lacks this advantage.
2. Inshore fire-support ship (IFS). The inshore fire-support ship, a recent addition to the fleet, is designed for
providing close support to troops in amphibious landings. The major armament consists of rapid fire rocket launchers.
A crew of 162 will man this 245-foot vessel, whose twin screws are powered by diesel engines. The displacement of
the ship is 1,500 tons.
22B3. Projectiles and fuzes
The selection of the projectile type to be used in support of troops depends upon the type of target and the effect
sought on that target. High-capacity (HC) projectiles are designed especially for use in shore bombardment. They
have a great explosive content at the expense of penetrative ability and produce a heavy blasting and shrapnel effect.
HC is therefore suitable for neutralization or for destruction of relatively light installations. Antiaircraft common (AAC)
projectiles are similar to HC projectiles in explosive and penetrative qualities. Their effective bursting radius of
35 to 50 yards makes them most satisfactory for close-support neutralization fire. Armor-piercing (AP) and common
(COM) projectiles are designed to penetrate armor plate before detonating. Their use in shore bombardment is
limited to fire on fixed enemy defenses such as concrete pillboxes and blockhouses which cannot be reduced by HC
projectiles. White-phosphorus (WP) projectiles have been found very useful for screening, incendiary, and
antipersonnel effect. They may also be used as identifying or marker shot to identify salvos, to permit spotting when
the impact burst is invisible due to foliage, or to give a prearranged signal to the troops supported. Illuminating (Ilium)
projectiles are used to provide illumination only.
The type of fuzes used with HG, AAG, and WP projectiles may be varied to meet different objectives. Mechanical
time fuzes may be used to provide air bursts for maximum effect against personnel and light equipment. They should
be set to burst 25 to 50 feet directly above the target. Proximity fuzes accomplish the same purpose with greater
accuracy and less difficult fire control, as they compensate automatically for variations in ground elevation.
Point-detonating fuzes, like proximity fuzes, require no advance setting but produce a lower and more concentrated
burst, often desirable for demolishing equipment. Base-detonating fuzes are, of course, required whenever armored
or other heavy structures must be penetrated.
22B4. Phases of support
It is convenient to divide the support for a landing operation into three general phases as follows:
1. Pre-landing bombardment. This phase, which may commence well in advance of D-day, utilizes quick raids by
surface ships to inflict damage and cause confusion, after which the ships retire. Similar strikes may be carried out
by aircraft during this phase.
More often the bombardment group will move into position a few days prior to D-day and commence its schedule
of prearranged fire which may continue right up to H-hour (the time of landing of the first wave of troops) or may
be interrupted by retirement of the bombardment group for reasons of safety.
During this period, the effect sought by the bombardment is destruction of beach defenses, gun control and
observation posts, or any defenses which could effectively oppose the landing. Slow, deliberate, close-range
destructive fire is used whenever it is possible. In this, as well as in later phases, an attempt is often made to
conceal the actual landing beaches by a schedule of fire covering other areas. The number of ships engaged in
the pre-landing bombardment, its duration, and the type of ammunition expended will depend upon such factors
as the number of ships and planes available, the logistics (especially ammunition supply), and the nature of the
terrain and its defenses.
In addition to its primary purpose of destroying designated targets which may hamper the landing, the force is
often called upon to provide cover for minesweepers, underwater demolition teams, and hydrographic survey
vessels. During the night it may engage in harassing fire to break down enemy morale. During the last hours prior
to H-hour it may be called upon to provide interdiction fire to prevent assembly of reinforcements and their
movements into the area of the landing beaches to man installations or repair damaged equipment. On D-day,
prior to embarkation of troops, the bombardment of strong resistance points will be intensified. The force may
be called upon to cover the final mine sweeping operations and the approach of the attack force, especially the
transports. When the transports are in position and the landing beaches are disclosed to the enemy, fire can be
concentrated on strong points which intelligence reports or observation indicate have not been destroyed.
During this period, also, air strikes are often scheduled to bomb and strafe the beaches. Provisions must be
made to control fire so as to avoid hitting friendly planes.
2. Support during the landing. The primary missions of naval gunfire in this phase are to protect the transports
while the landing force is embarking in boats, to silence batteries which might destroy the assault waves as the
boats move in to the beach, and to cover the actual landing of troops. The barrage must be lifted inland or shifted
to the flanks as the troops near the beach to avoid hitting the landing force as well as to neutralize strong points
from which destructive crossfire could be poured on the beaches. In addition to close supporting neutralization
fire on the landing and adjacent areas, deep supporting fire must be concurrently delivered to prevent enemy troop
movement toward the landing area and to neutralize more remote opposing enemy defenses.
During the last few minutes, as the first wave nears the beach, a final air strike often parallels the beach, strafing
and driving the enemy to cover. Also just before the landing, the rocket and mortar ships close inshore will deliver
a devastating barrage, saturating the whole beach area.
The rapidity of events and general lack of information from troops being supported during and immediately following
a landing require that most of the supporting fire be planned in advance, for delivery according to a carefully
formulated and coordinated time schedule.
It is essential that close and deep supporting fire be scheduled to continue after the landing, in order to neutralize
enemy opposition which would hinder the rapid establishment of organized troop units ashore. The post landing
schedule of fire must be carefully planned for coordination with the estimated troop advance ashore, but must be
capable of quick modification to permit repeating, extending, or discontinuing any portion of the schedule when the
advance differs from that expected. The duration of the scheduled fire after H-hour must extend well beyond the
estimated time required to establish effective naval gunfire control agencies ashore.
In the case of heavily defended objectives, scheduled fire for close support must continue at least an hour after the
landing, and for deep support at least 4 hours.
3. Support for troop advance ashore. Naval gunfire is employed after the landing phase to assist the advance of
troops to their final objectives. Close supporting fire from ships assigned to them, daily or upon special request, is
made continuously available to troop units in assault. Deep support, including daily destructive fire missions,
preparation fire for troop attacks, and night harassing fire, are scheduled for daily execution in fulfillment of troop
requests. This phase of naval gunfire support commences upon the completion of the prearranged scheduled fire in
support of the landing and continues until naval gunfire is no longer required for support.
22B5. Land-target problem
Naval gunfire against targets on land offers essentially the same problem as firing at a ship dead in the water, except
for the following additional considerations:
1. Ships position. As mentioned before, the geographical position of the firing ship must be continuously and
accurately fixed, as from this are determined the range and bearing of the target in many instances when indirect fire
must be used.
2. Terrain. Terrain features make correction of the fall of shot a difficult problem. Since range tables and rangekeeper
solutions in main-battery systems assume the point of fall to be in the horizontal plane, the elevation of the target above
sea level must be compensated for in the fire control solution. Figure 22B1 illustrates the errors resulting when the
range of a land target is taken from a chart and the targets elevation is not considered. When dual-purpose guns are
used for shore bombardment, the antiaircraft fire control systems provide a ready solution to this problem. Terrain
features also affect the size of the pattern in range; a forward slope decreases it, and a reverse slope increases it.
Figure 22B2 illustrates these effects.
3. Current effects. The set and drift of the current will affect the solution of the fire control problem. When
determined, drift may be entered into the rangekeeper or computer as target speed; the direction of the set is
reversed and introduced as target course.
4. Parallax. In order to cover area targets more effectively with the shots of individual salvos, it may be desirable to
increase the deflection pattern by setting the horizontal parallax correctors at infinity (i. e., removing horizontal parallax
correction from the gun battery).
5. Varying ammunition. Frequent and rapid changes in the targets to be engaged require ready accessibility of various
types of ammunition and fuzes.
6. Principles of employment. Effective support of troops by naval gunfire is dependent on certain principles of
employment and techniques of de livery of that gunfire which might be called tricks of the trade. The following
paragraphs briefly discuss these. Prerequisites of effective support are the proper alignment of the fire control system
and gun battery, rapid and reliable internal and external communications, and well-trained ship control, fire control,
and gun control personnel. The primary duty of naval gunfire in all phases of the support is the immediate and effective
silencing of heavy enemy weapons which open fire on our forces. It is essential that a counter-battery plan satisfying
all contingencies be kept in constant readiness and that fire-support ships be ready and alert at all times for the
delivery of this fire. When the source of enemy fire is not known, heavy counter-battery fire on suspected sources is
delivered pending the determination of the exact location of the enemy battery. The whereabouts of friendly forces
must be kept in mind during such an attack.
Only by thorough familiarity with the land areas assigned, achieved through repeated firing, observation, and analysis,
can the most effective fire be delivered by ships. The shifting of ships to different areas of responsibility, or frequent
shifting of fire between targets widely separated in the same general target area, is avoided.
Unlike surface or air actions at sea, naval gunfire support requires moderately low speeds. The use of high speed in a
firing ship requires it to make frequent course reversals in order to remain in its assigned sector, results in unacceptable
inaccuracies in establishing the shipâ€™s position for indirect fire, takes the ship too quickly beyond effective firing
positions limited by terrain features, and may result in prohibitive interference with other activities offshore. A low
speed is usually selected which will allow good control of the ship and the supporting fire, consistent with the tactical
situation and the submarine menace. If necessary, the ship will lie to or anchor, maintaining desired heading by the use
of the engines. Best results for indirect fire will be obtained if ships steam on a steady course at a constant low speed.
Direct fire is employed whenever possible, although indirect methods must always be employed when visible points of
aim are not available. Indirect fire requires more ammunition and time than direct fire for equally destructive success.
It requires air or ground observation of the fall of shot in order to ensure hits on point targets. The effectiveness of
naval gunfire is increased by the employment of an air spotter working with a ground spotter.
Once established, the maintenance of the hitting gun range and deflection is essential to effective destructive fire.
Periods of continuous slow fire with reduced salvos are therefore preferable to more rapid fire interspersed with
relatively long non-firing intervals.
The decisive destruction of heavy defenses is greatly enhanced by very close-range, slow, deliberate, direct fire
against such installations. Fire-support ships usually operate as close inshore as safe navigation, the tactical situation,
enemy shore batteries, and the type of fire required will permit. Close supporting neutralization fire on the landing area
in support of troops about to land, although scheduled to be shifted there from on a time basis relative to the
estimated time of H-hour, must be adjusted according to the actual position of the troop landing craft. From reports
of landing-craft progress received, but primarily from own observation when possible, fire-support ships individually
determine when their fire is about to endanger troops nearing shore, and accordingly shift the fire from the landing
Close cooperation between ships and the troop units to which assigned for support is essential for maximum
effectiveness. Interchange of information between supporting ships and troop units results in more intelligent and
effective fire support. Of particular importance in this connection is the safety requirement that all fire-support ships
maintain an up-to-date plot of own troop front-line positions as periodically announced by elements of the landing
force. This not only prevents endangering own troops, but permits selection of the most suitable line of fire with
respect to troop lines. Another consideration is the necessity for safeguarding friendly aircraft operating in the area.
Illumination of land areas by naval star shells is effective in preventing enemy counterattacks, infiltration, and the
movement of enemy troops at night. Its morale-boosting effect on our own troops generally results in requests for
exorbitant star-shell expenditures to produce unnecessary illumination of the land area throughout the night. Except
during actual enemy counterattacks, star shells fired at a reduced rate and at irregular intervals normally discourage
enemy movement. Maximum benefit from the limited supply of star shells available requires judicious control and
coordination by troop units to avoid silhouetting of own forces ashore and afloat. When delivering illumination fire, the
line of fire must be so adjusted with relation to our front lines that friendly troops are not endangered by star-shell
bodies. Except in rare instances, searchlight illumination for troop support is generally unsuccessful; it almost
invariably draws enemy fire on the ship employing it.
7. Requirements for neutralization. The volume of fire required for neutralization of an area is difficult to establish. The
standard volume established prior to World War II prescribed the equivalent of sixteen 75-mm projectiles per minute
per 100-yard square as being sufficient for neutralization. Although the experiences of World War II showed this to
be entirely inadequate in many instances, it is still a valuable guide which may be modified as conditions dictate.
Experience proved that the blast effect of bursting projectiles had been highly overrated in neutralizing effect; it was
found instead that neutralization primarily depended upon the casualties produced or threatened by flying fragments.
Fragmentation effects vary greatly, even in the case of projectiles which are identical, because they depend upon such
factors as angle of fall and terminal velocity. For example, the number of casualties inflicted may double with an
increase in angle of fall from 100° to 60°. The effectiveness of fire for neutralization will also vary in accordance with
the terrain, the types of enemy installations, and the quality of the enemy troops. Extensive studies of neutralization
effects in World War II are being made in an effort to establish a new and more accurate neutralization factor.
8. Target intelligence. Before undertaking any bombardment of land targets, a thorough familiarity with the terrain and
hydrographic features of the objective, and with the location of profitable targets, must be acquired. The study of
available charts, maps, aerial photographs, radar PPI simulations, mosaics, and other pertinent information will be
necessary for rapid, effective troop support. Normally these charts, maps, photographs, and target information will be
furnished each fire-support ship prior to the operation. The systematic destruction of defenses requires the continuous
assembly and evaluations of targets known before hand, and of those discovered in the course of the operation.
Damage assessment must be based upon visual observation and photo-analysis. A common error is over-optimism as
to the effectiveness of naval fire against land targets.
9. Military Grid Reference System. Rapid and accurate means for designating the location of targets is an essential
feature of naval gunfire support. It should be obvious that the troop unit supported and the supporting ship must use a
common map. Although they need not be of the same scale, and seldom are, the target maps must be identical
regarding terrain features and the method of locating points thereon. Like other techniques of naval gunfire support,
the development of a system of target location designations has passed through several stages, following generally a
grid-system method. In this method, the land and sea areas at the objective are divided into squares by north-south
and east-west lines, which are numbered. These lines are called grid lines.
The Military Grid Reference System imposes vertical and horizontal reference lines over a projection of the earths
surface. Its purpose is to simplify and to increase the accuracy of reporting and plotting in military operations. The
grid reference system is based on two projections: the Universal Transverse Mercator (UTM), and the Universal
Polar Stereographic (UPS).
a. Universal Transverse Mercator. Any projection is simply a method of depicting a spherical surface on a flat piece
of paper. The familiar Mercator projection, long used in navigational charts, mathematically develops the surface of
the earth on a cylinder which is tangent to the earths surface at the equator. The Transverse Mercator uses the same
principle, except that the cylinder is tangent to the earths surface along the great circle of a meridian, at right angles to
the equator. In the UTM, both meridians and parallels appear as slightly curved lines. See figure 22B3. There is very
little distortion near the line of tangency, so that a relatively narrow band of longitude can be accurately shown from
pole to pole.
Universal Transverse Mercator coverage is based on five separate spheroids which depict the earth from 80° south
latitude to 80° north latitude. The spheroids are mathematically corrected to allow for the irregularities of the oblate
spheroidal shape of the earth. When pieced together, the spheroids join each other on exact degrees of latitude and
on exact even degrees of longitude.
Between latitudes 80° N and 80° S, the UTM grid divides the earth into areas 6° east-west by 8° north-south.
Columns (6° wide) are numbered 1 through 60 consecutively, starting at the 180° meridian and proceeding easterly.
Rows (8° high) start at 80° S and proceed northerly to 80° N. They are lettered alphabetically C through X, omitting
letters I and 0.
The method of identifying the 6° by 8° areas is called grid zone designation. Grid zone designation for any area
established by the columns and rows is determined by reading right-up on the chart. As an example, column
designation 2 and row designation P produce grid zone designation 2P.
Each grid zone designation is subdivided into 100,000-meter squares, as shown in figure 22B3. The 100,000-meter
squares are also laid out in columns and rows, but these are identified by letters only.
As shown in figure 22B3, the 100,000-meter squares are lettered without regard for boundaries of separate grid
zones. Columns are lettered A through Z (omitting I and 0) beginning with the 180Â° meridian and proceeding east
along the equator. Since the l00,000-meter squares are established about the central meridian of each zone, UTM
projection creates partial squares at the edges of each zone. The partial squares create partial columns which are
included in the alphabetical progression just as though they were made up of complete 100,000-meter squares. In
lettering the columns, the alphabet is repeated every 18Â°. Figure 22B3 shows a complete cycle of lettering.
The rows of 100,000-meter squares are lettered alphabetically from south to north, A through V, omitting I and 0.
The alphabet is repeated every 2,000,000 meters (20 squares). Squares having the same identifying letters are
separated as follows:
The row alphabet for each odd-numbered UTM zone begins at the equator; for each even-numbered UTM zone, it
begins 500,000 meters south of the equator. Thus, squares carrying the same letters are effectively separated by
18Â° of longitude.
Location of a particular 100,000-meter square is determined by reading right-up, first the column letter and then the
row letter. Thus, MT in figure 22B3 is found by reading right along the column letters to M and up the row letters to
Each 100,000-meter square is further divided to provide, eventually, a 100-meter square reference area. First, grid
lines spaced 10,000 meters are placed within each square. Lines are placed vertically and horizontally so that their
intersections form right angles. Since the grid lines form one hundred 10,000-meter squares, only two digits are
required for designation 00 to 99. Designation of the 10,000-meter squares begins in the lower left corner of the
100,000-meter square. The 10,000-meter square in this corner is designated 00; the one immediately above is 01,
the next 02, and so on until the top square in the upper left corner carries 09. The square immediately to the right of
square 00 is 10, the next is 20, and so on to 90, the square in the lower right corner of the 100,000-meter square. In
other words, the 10,000-meter squares are numbered up each column from the 00 column to the 90 column.
Each two-digit 10,000-meter square is further divided into 100 squares by placing grid lines at 1,000-meter intervals,
vertical and horizontal, perpendicular at the crossings. Designation of the resulting 1,000-meter squares requires four
digits. Two of the four digits are taken from the 10,000-meter square in which the particular 1,000-meter square is
located. For example: In the 1,000-meter square designated 6957, digits 6 and 5 are keyed to the 10,000-meter parent
square, 65. Figure 22B4 shows the location of area 6957 within square 65. Actually, area 6957 is square 97 within the
10,000-meter square 65.
For accuracy in pinpointing targets, it is necessary to break down further the 1,000-meter squares. Formerly, a
system called target area designation (TAD) was used for this purpose. Each 1,000-meter square was divided by
grids at 200-meter intervals, making twenty-five 200-meter squares, labeled A through Y. The lettering started at the
upper left corner of the square, and the alphabet progressed row by row across, finishing at the lower right corner of
the square. Under this system, a 200-meter square could be designated by adding the letter to the four-digit 1,000-
meter square. For greater accuracy, the individual 200-meter square was broken down into areas designated by
numerals 1 through 5, providing enough accuracy for the spotter to adjust salvos to hit the target.
The U. S. Navy Hydrographic Office no longer prints the 200-meter grid lines, the TAD instructions, or the letter
designation for the 200-meter squares on grid charts. Since this is fairly recent policy, charts bearing this system will
probably be issued until the present supply is exhausted. However, the TAD system is no longer authorized for U. S.
Navy use, and reference to it on available charts is to be ignored.
The authorized method for reducing the reference area to a 100-meter square requires six digits. To illustrate,
consider the previous example where the 1,000-meter square was 6957. Adding two digits divides this area into
tenths, or 100-meter squares. Thus, in the designation 693578, the two additional digits (3 and 8) mean three-tenths
(300 meters) east from the southwest corner of the 1,000-meter square 6957, and eight-tenths (800 meters) north
from the southwest corner of the square. The east distance is always placed between the second and the third digits
of the 1,000-meter designation, and the north distance is placed at the end. In the final figure, 693578, observe that
the first three digits indicate distance east of the southwest corner of the original 100,000-meter square, and the last
three digits indicate distance north of the southwest corner.
A military grid reference consists of a group of letters and numbers which indicate (1) the grid zone designation, (2)
the 100,000-meter square identification, and (3) the grid coordinates; that is, the numerical reference of the point
expressed to the desired accuracy. Examples:
52SCU locating a point within a 100,000-meter square.
52SCU65 locating a point within a 10,000-meter square.
52SCU6957 locating a point within 1,000 meters.
52SCU693578... locating a point within 100 meters.
As a matter of practical referencing in a shore bombardment problem, both the grid zone designation and the
100,000-meter square identification are generally omitted. The grid reference box shown as a part of the marginal
data of every chart specifies the maximum distances beyond which omissions in reporting are not permitted.
b. Universal Polar Stereographic. The projection used for the polar areas is the polar stereographic covering the
limits from 80°N to 90°N for the north polar area, and 80°S to 90°S for the south polar area. The system for griding
the poles is called the Universal Polar Stereographic.
Stereographic projection is conformal, but instead of the plane for projection of the area being tangent to the pole,
for the UPS system, it is parallel to the plane of the equator, cutting through the latitudes 81° north and south. With
the plane at this area, a minimum variation of scale is obtained over the entire UPS system.
The north polar area is divided into two parts by the 180° and 0° meridians, the half containing the west longitudes
identified as zone Y and the half containing the east longitudes as zone Z. The south polar area is similarly divided
along the 0° and 180°meridians, the west longitude half identified as zone A and the east longitude identified as
In the north polar area the l80°-0° meridians coincide with an even 100,000-meter vertical grid line and the
90° W-90° E meridians coincide with an even 100,000-meter horizontal grid line. Grid north coincides with the 180°
meridian from the pole. In grid zone Y, the 100,000-meter columns (right-angle lines to the 90° W-90° E meridians)
are labeled J through Z (I and 0 omitted), alphabetically from left to right. In grid zone Z, the 100,000-meter columns
are labeled A through R (omitting I and 0), alphabetically from left to right. Letters D, E, M, N, V, and W are
omitted to avoid confusing the 100,000-meter squares with those of the adjoining UTM zones.
Starting at the 80° parallel and reading toward grid north, the 100,000-meter rows (at right angles to the 180°-0°
meridians), are labeled A through Z (omitting I and 0).
Identification of the 100,000-meter squares is accomplished by reading right-up, first the column letter followed by
the row letter.
For the south polar area the plan is similar, except that grid north is coincident with the 0° meridian from the pole.
Zone A at the south pole is equivalent to zone Y at the north pole, and zone B is equivalent to zone Z.
The 100,000-meter squares are subdivided into 10,000-meter and 1,000-meter squares in the same manner as
the UTM system breakdown, and grid values are always read right-up.
Fire-support ships are provided with approach charts and bombardment charts for use on their dead-reckoning
tracers. These charts are complete in hydrographic as well as topographic detail, and both have a grid system
overprinted on them. These charts are of particular use in the delivery of indirect fire, and will be discussed later.
22B6. Shipboard problem of naval gunfire support
1. Direct fire. Targets which are visible from the firing ship offer the simplest fire control problem to the ship, and
their destruction is easier than those targets which require indirect fire. When the target can be seen, the director can
furnish accurate target bearing and elevation. These, with a present range which can be measured, ensure an accurate
fire control set-up which should result in early hits. Direct fire is controlled as it would be for fire against enemy ships
except that (1) at short ranges better accuracy may be obtained if the gun pointers control gun elevation and firing
and (2) when the ship is providing call fire support, the fire will be directed, controlled, and spotted by the shore
2. Indirect fire: use of bombardment chart. Given an accurate bombardment chart, and knowing the exact position of
own ship, it is possible to measure off range and bearing to any land target that has been designated in advance and
to hit the target without using directors or rangefinders.
The ships position is accurately determined by navigational methods, using positively identified landmarks, and is
plotted on the bombardment chart. Since own ships course and speed are known, future positions may be projected
ahead along the ships track by dead reckoning. A future position, usually one minute ahead, is chosen, and from this
point bearing and distance to the designated target are picked off the chart. These values of target range and bearing,
together with own ships course and speed, are set into the rangekeeper or computer which is being used to generate
the solution. Target speed is set on zero. During this period, the time motor is off. When the ship passes through the
position chosen, Mark is given by the plotter and the time motor of the computer is turned on. The computer should
now generate present values of target range and bearing that agree with the actual measured values. These values,
together with a fixed setting of altitude, based on the actual height of the target, are used to make up gun orders to hit
the target. At stated periods, usually every minute after the initial setup, Mark is given and the computed values are
compared with the measured values. If they do not agree, since the target is motionless, the error must be due to
some factor affecting the position of the ship.
The set and drift of the current will cause such variation, and corrections for this effect may be compensated by
introducing the drift and set of the current as target speed and reverse of target course respectively. At any time after
the computed solution agrees with the measured values, the initial ballistic can be applied, and fire opened on the
3. Indirect fire: Point OBOE method. This method of indirect fire was devised primarily for older ships with fire
control systems and range-keepers incapable of correctly generating range and bearing to a designated grid point. Its
use, however, even by the newest ships is advantageous under certain conditions such as when no shore spotter or
air spotter is available for observing the fall of shot. The method requires a visible point of aim (designated â€œPoint
OBOE) near the target, as well as the accurate location of the target and Point OBOE on a map.
In practice, the director line of sight is kept continuously trained and ranged on the point of aim (Point OBOE) to
give a continuous range and bearing solution to this point. Salvos are initially fired at Point OBOE as a check on the
gun ballistic, and as soon as the mean point of impact has been spotted to hit, range and deflection spots necessary
to hit the invisible targets are applied. Point OBOE should be selected so that the limits of the spot dials do not have
to be exceeded to reach desired targets.
Since the motion of the firing ship continuously changes the values of the offsets from the point of aim, frequent
changes in these offset spots must be made to ensure hitting the target. This problem is illustrated in figure 22B5.
One way to determine correct range and deflection spots continuously is to use a small transparent overlay on which
are inscribed 100-yard squares drawn to the same scale as the chart. With the center of the gridded overlay on Point
OBOE, and the grid lines oriented to the direction of the line of sight from the ship, range and deflection spots to hit
the designated target may be read directly from the grid overlay.
4. Indirect fire: functions of CIC. The primary function of CIC in
naval gunfire support is to keep an exact check on the ships
position and from this to determine ranges and bearings to targets
designated for indirect fire. It can be readily appreciated that the
accuracy of fire, when using the method previously described,
depends primarily on the skill of the CIC team. CIC also keeps a
record of own troop front-line positions, target locations, and
other information pertinent to the support of the troops ashore. It
acts as the clearing house for information to and from the shore fire
control party and air observer, with whom it has direct voice radio
communication. Thus in naval gunfire support, CIC keeps the ships
commanding officer, gun control, and plot advised regarding the
requirements for support; furnishes the information necessary to
provide the support; and gives the shore fire control party such
information as may be necessary or useful. In addition to target
range and bearing, CIC must determine, from contour lines of the
bombardment chart, the elevation of the target above sea level and
send this to the plotting room so that range error resulting from this
elevation may be corrected in the computer.
On heavy ships (battleships and cruisers) the above functions of
CIC are often performed in a section of the plotting room. This
leaves the ships CIC free for the other vital duties it must perform.
5. Special firecontrol problems of naval gunfire support. Targets
which are located on the far slope of a hill or similar terrain feature
lying between the firing ship and target present a particularly
difficult problem to the flat trajectory of naval gunfire. This problem
(defilade fire) requires obtaining an angle of fall which will clear the
crest of the hill and be steep enough to hit the target beyond.
When this situation occurs, the angle of fall is chosen which is
greater than the angle of the reverse slope. Two solutions are then
available. The ship may either increase the range to obtain the
angle of fall selected, or it may use reduced-velocity charges at the
shorter range to obtain this selected angle of fall.
In figure 22B6, which illustrates this problem and its solutions, A
is the trajectory produced by standard service charges and is too
flat; B is the trajectory which can be obtained by using
reduced-velocity charges; C is the trajectory which can be
obtained with standard service charges by increasing the range.
In the event it is necessary to fire over friendly troops occupying an
elevated position between the firing ship and the target, it is
necessary to determine the elevation of the target, the elevation of
the troop position, and the differences between the two. Call this
difference y, and the horizontal distance between the troop
position and the target x. By referring to trajectory curves, you can
determine the range at which the abscissa x yards from the point of
impact is safely greater than the difference in elevation y. This is the
limiting range outside of which it is safe to fire.
22B7. Spotting by target grid system
Spotting, as it applies to naval gunfire in general, was discussed in chapter 18. All the general principles contained
therein apply in shore bombardment spotting, but additional considerations apply also, especially when spots are to
be made by a shore fire control party.
A spotter ashore must be advantageously located to observe the fall of shot. In most cases this requires that he be as
close as possible to the enemy positions which will have to be taken under fire; this presents him with a very serious
front-line problem of survival.
Spots made by an observer aboard the firing ship are naturally oriented to the line between the firing ship and target
(called the gun-target line). Spots made from aircraft can be oriented readily to the gun-target line, since both the gun
and the target are normally within the aircraft observerâ€™s field of vision. But spotters ashore are frequently unable
to see the firing ship and, so long as they were required to make their reports in relation to the gun-target line, this
seriously limited the value of the information sent by the spotter to the ship.
To simplify this problem for the spotter, the Army Artillery School at Fort Sill developed the target-grid system for
use in spotting the fall of shot on land. As a result of trials in joint exercises, the target-grid system has been
incorporated into the Standard Spotting and General Shore Bombardment Procedure for use within the naval service.
The objective of this system is to permit the observer to spot the fall of shot just as he sees it along his own line of
sight to the target, called the observer-target line, irrespective of the position of the firing ship and of the gun-target
line. The procedure is briefly outlined as follows (refer to fig. 22B7).
1. The observer, in his call for fire must give the azimuth from himself to the target; direction OT in the illustration.
2. The observer makes all his observations and corrections with respect to the observer-target line (OT).
3. The CIC or plotting room crew converts the corrections of the observer to corrections with respect to the gun-
target line (GT).
4. The plotting room crew introduces into the rangekeeper (computer) the spots corrected to the gun-target line.
22B8. Grid spot converter
The grid spot converter is a device used to convert graphically the corrections given by the spotter from the OT line
(spotters line of sight) to the GT line (ships line of fire). It consists of two superimposed concentric circles with
horizontal and vertical lines etched on them, forming squares, each dimension representing 100 yards. The lower circle
is etched in black on the face of the converter; it is stationary. Its circumference is graduated counterclockwise in degrees
from 0° to 360°, with 0° at the top. The 0-180 diameter of this circle is a black arrow, with the arrowhead at zero degrees.
The upper circle is etched in red on a movable, transparent plastic disc; this disc is mounted concentrically over the lower
circle, so that it is free to rotate about its center. The circumference of the upper disc is graduated counterclockwise in mils
from 0 to 6, 400, with 0 mils at the top. The 0-3, 200 diameter of this disc is a red arrow, with the arrowhead at zero mils.
The lower disc is the own ship disc, and the black arrow represents the GT line. The upper, movable disc is the observer disc,
and the red arrow represents the OT line.
The grid spot converter is used as follows (see fig. 22B8):
1. The converter operator obtains the true azimuth of the GT line in degrees by reading the true target bearing on the own-ship
dial group of the computer. He makes a mark with a grease pencil at this azimuth on the lower (black) disc. He then obtains
the azimuth of the OT line from the observer (spotter) via CIC. He makes another mark at this azimuth on the upper (red) disc.
2. The operator then rotates the upper disc until the two pencil marks are opposite each other. In the figure, GT is 1400 and
OT is 1,500 mils. See pencil marks. The red and black arrows now indicate the angular relationship of the observers line of
sight and the ships line of fire.
3. When a spot is received from the spotter, the operator starts at the center of the upper disc, which represents the burst, and
plots Right 200; add 500 along the lines perpendicular to and parallel to the red arrow. The point plotted then represents the
target, which is marked with grease pencil. He now goes back to the burst (center) and counts off the squares to the target,
on the lower disc, perpendicular to and parallel to the black arrow. This gives a spot of Left 300, add 450, which is relative to
the ships line of fire. This is the spot which is applied to the computer (Left 300 is in yards, and must be converted to mils
before it can be applied).