RESTRICTED

21 APRIL 1949

        OPERATING INSTRUCTIONS
        1. Ordnance Pamphlet 1719 describes procedures for operating Gun Fire Control System Mark 37. These procedures differ from the instructions for operating the different components of the system in the organization of the text according to tactical situations expected to be met with the fire control system.
        2. The procedures described in Ordnance Pamphlet 1719 are not intended to establish doctrine for the operation of the Gun Fire Control System Mark 37. They are suggested procedures which embody principles incorporated by the design engineers and the results of experience in system operation. Where alternate procedures are suitable for different situations, these too are described. The Bureau welcomes additional suggested procedures and will revise Ordnance Pamphlet 1719 to keep the procedures current with changes in equipment design and/or tactical situations.
       3. This pamphlet does not supersede any existing publication. Additional information on the components of the Gun Fire Control System Mark 37 may be found in the following publications :

        Associated Stations

        Director Mk 37

        Fire Control System Mk 37

2. Primary Control Circuits on a Two-

        System Ship

        Equipment Mark 12)

3. Radar Control Consol Mk 5

        for Mk 37 (Equipped with Radar

5. Radar Tracker (Automatic)

6. Control Unit (Power)

7. Stable Element Control Panel

21. Operation of Gun Fire Control

8. Stable Element Mk 6

9. Selector Drive Mk 1

10. Control Unit Operating Controls—

        Computer Mk 1

22. Control Officer's Station—Gun Direc-

11. Computer and Indicator Unit Operat-

        ing Controls—Computer Mk 1

12. Radar Operator's Station—Gun Direc-

        for Mk 37 (Equipped with Radar

         tor Mk 37 (Equipped with Radar

        Equipments for Mk 12 and Mk 22

13. Radar Operator's Station—Gun Direc-

        tor Mk 37 (Equipped with Radar

        Equipment Mk 25)

14. Pointer's Station—Gun Director-

        Mk 37 (Equipped with Radar

        Equipments Mk 12 and Mark 22)

        Equipments Mk 12 and Mark 22)

15, Trainer's Station—Gun Director

        tor Mk 37 (Equipped with Radar

        Equipment Mk 12 )

16. Trainer's Station—Gun Director

        tor Mk 37 (Equipped with Radar

        Equipment Mk 12 )

30. Effect of Sensitivity Push Button on

38. Radar Console Mk 5

31. Operation of Gun Fire Control System

        Mk 37 Against Obscured Air Targets

32. Operation of Gun Fire Control System

41. Time Constants for Surface Targets

        Mk 37 (Equipped with Radar

43. Assistant Control Officer's Station—

        Air Targets

33. Pointer's and Trainer's Station—Gun

        Director Mk 37 (Equipped with

45. Operation of Gun Fire Control System

        Radar Equipment Mk 25)

34. Radar Console Mk 5

35. Operation of Gun Fire Control System

        Mk 37 Against Visible Surface

         Mk 37—Offset Fire—Method 2

        Targets. Method 1.

36. Operating Controls for Surface Fire—

        Computer Mk 1

         Problem in Figure 48

        Equipment Mk 12 )

Purpose
This pamphlet outlines procedures for operating the Gun Fire Control System Mk 37 (frontispiece). These procedures embody operating instructions recommended by the designers of the equipment plus certain modifications of these procedures that have been evolved from actual combat operation of the system. These instructions assume that the user is familiar with the technical details of the Gun Fire Control System Mk 37 as described in the following publications or in publications superseding them :

OP 1060 Gun Director Mk 37.
OP 1063 Stable Element Mk 6.
OP 1064 Computer Mk 1.
OP 1076 Radar Equipment Mk 12.
OP 1153 Radar Equipment Mk 22.
OP 1651 Radar Equipment Mk 25.

The nature of the Gun Fire Control System Mk 37 suggests the following division of the presentation of operating instructions:

a. Standby Condition
b. Air Targets
c. Surface Targets
d. Shore Bombardment

In this pamphlet a chapter is devoted to each of these divisions. The chapters containing instructions for operation against air targets and surface targets are further subdivided according to the tactical situation; each giving the preferred methods of engaging visible targets (i.e., surprise attacks, daytime surface engagements, etc.) and obscured targets (i.e., night attacks, long range engagements, etc.). In certain methods are not for different tactical situations but are secondary methods of utilizing the equipment to cope with the same tactical problem. Where more than one method of operation for any tactical situation is given, the first method described is recommended if the operating conditions and the material condition of the equipments permit such a procedure. It is recognized, however, that in the use of certain ordnance equipment which requires human supervision, control, or operation, there are factors associated with the personalities of the available humans which, for a particular ship, may make most effective a procedure considered of secondary merit by other organizations.

The chapter on shore bombardment describes methods that may be employed for each of the following situations:

a. Visible shore target;
b. Obscured shore target displaced a known distance from a point of aim;
c. Obscured shore target with no suitable visible point of aim, but located in a known chart position.

Scope
The procedures established herein are not gunnery doctrine. Cognizant commanders may find these procedures useful in formulating gunnery doctrines in that they may assist in defining the method of using the equipment which the doctrine prescribes for various tactical situations.

This description is generally applicable to all Gun Fire Control Systems Mk 37. It is specifically applicable to a system including the following components:

Bearing Indicator Mk 10.
Change of Range Receiver Mk 1.
Computer Mk 1 or Computer Mk 1A.
Gun Director Mk 37.
Radar Equipments Mk 12 and 22, or Mk 25 and Mk 32.
Rangefinder Mk 42.
Range Indicator Mk 5.
Range Spot Transmitter Mk 2.
Searchlight Control Transmitter Mk 1.
Selector Drive Mk 1.
Slewing Sight Mk 2 or 4.
Spot Transmitter Mk 1.
Stable Element Mk 6.
Star Shell Computer Mk 1.
Star Shell Spot Transmitter Mk 1.
Target Course Indicator Mk 1.

Introduction
The standby condition of the Gun Fire Control System Mk 37 is its condition when targets are expected momentarily, but with no specific targets yet known. It is the materiel condition which permits engaging any type of target with minimum delay. It is apparent that the system must be thus ready for action both when fully manned (general quarters), and when the ship is in a reduced condition of readiness for action (condition watches), where there is a reduction in the personnel available to man the system. This chapter describes the steps necessary to place the Gun Fire Control System Mk 37 in the standby condition both with general quarters and condition watch crews. Throughout these instructions' where, depending on the number of personnel available, possible differences exist in the operation of the equipments, these differences will be noted.

Communications
This section indicates the intercommunications that should be established among the components of the system and associated stations in order for operation to be effective. Two basic schemes are given. Certain variations within each are possible without decreasing effectiveness. Some of these variations are mentioned herein. Both schemes have had extensive use in war, and both are suitable for adaptation to the new developments in fire control installations (including target designation equipment) that are beginning to appear in various ship classes. Observe that the telephone circuit designations used in the two schemes do not conform to those in effect in certain ship classes; however, the selection of the suitable circuit in such cases should be straightforward, based on circuit interconnections and outlet arrangements.

Scheme 1. Figure 1 is a block diagram of a typical communications setup for a Gun Fire Control System Mk 37 in control of a portion of the ship's antiaircraft battery. Considerable fleet experience indicates that this setup is satisfactory. Its principal features are as follows.

As shown by the figure, the air defense officer is given direct communication with the director control officer, the plotting room officer, and the evaluator via the air defense circuit (5JP). The control officers of other antiaircraft systems on the same ship may also be on this 5JP circuit. Since the air defense officer may receive target status information, target designations, etc. on this circuit from the evaluator at the target designation center; this information reaches the director control officer and the plotting room officer at the same time, thereby allowing more time to take appropriate action than if this information were to be relayed through several channels. The director pointer is placed on the 5JP circuit to maintain contact between the air defense officer and the director crew whenever the director control officer has switched to his gun control circuit (UP), or is standing at the slewing sight. The switchboard operator, in plot, is placed on the 5JP circuit in order that he may take direct action on orders involving switching operations such as changes in battery setups. The gun control circuit (UP) is used primarily to establish communications between the director control officer, the computer officer, and the mount captains. This circuit serves as the only means of communication from the mount captains to the director control officer as the battle announcing circuit (17MC) is not reversible. The assistant control officer on the UP circuit in the director normally acts directly for the director control officer in matters appropriate to the UP circuit when the latter is on the air defense circuit (5JP). The computer operator (elevation), mount and director trainers, and mount pointers are on the UP circuit for information only (such as early receipt of

2.1 THE IC ROOM

IC Switchboard
The following circuits should be energized at the IC Switchboard. All of these circuits do not appear on all ships, and in some installations certain of these circuits are paralleled; however, to make this procedure applicable to all installations, all of the circuits that should be energized are listed here.
     Energize:

GSL 115 V AC power supply.
IY Own ship speed.
2GS Gun train order.
2PA Gun firing.
2PD Bearing designation.
2U Cease firing.
2VB Salvo signal.
3GS Gun elevation order.
4GS Director train.
5GS Director elevation.
7GS Own ship course.
8GS Searchlight train order.
9GS Seachlight battle orders.
10GS Cross level.
13GS Fuze setting order.
14GS Director train control.
15GS Director elevation control.
17GS Direct current supply.
18GS Searchlight elevation order.
19GS Sight angle.
20GS Sight deflection.
22GS Deflection spot.
23GS Elevation spot.
24GS 6 V DC supply.
25GS Train parallax.
26GS Elevation parallax.
27GS Heaters.
29GS Director parallax.
31GS Range.
31PD Range designation.
32GS Range increments.
33GS Range spot.
42GS Star shell train order.
43GS Star shell elevation order.
50GS Level.
53GS Star shell fuze order.
62GS Star shell deflection spot.
63GS Star shell elevation spot.
73GS Star shell range spot.

2.2 THE RADAR ROOM

At the present time, most Gun Fire Control Systems Mk 37 are equipped with either Radar Equipments Mk 12 and Mk 22 or Radar Equipment Mk 25. The below-decks operations required to place these equipments in the standby condition are as follows:

Radar Equipments Mk 12 and Mk 22
    Line Switches:
        a. Set the Radar Equipment Mk 12 line switch at ON.
        b. Set the Radar Equipment Mk 22 line switch at ON.
Power Control Unit:
        a. Set the STANDBY switch at ON.
        b. Wait 10 minutes.
        c. Set the OPERATE switch at ON.
High Voltage Rectifier:
        a. Turn the DC voltage control until the DC output voltage meter reads 5.2.
Range Unit:
        a. Set the REMOTE-LOCAL switch at REMOTE.

Radar Equipment Mk 25
BEFORE ENERGIZING RADAR EQUIPMENT MK 25, check the following items:
    At the Radar Console Mk 5 (fig. 3) :
        a. Momentarily press the OFF push button.
        b. Check that the BATTLE SHORT lamp is extinguished.
At the Controller (Antenna Motor) (fig. 4) :
        a. Set the power switch at OFF. At the Radar Tracker (Automatic) (fig. 5) :Radar Tracker (Automatic) (fig. 5) :
        a. Set the power switch at OFF.
        b. Set the LOCAL-REMOTE switch at REMOTE.
At the Control Unit (Power) (fig. 6) :
        a. Set the main switch at OFF.
        b. Inside the Control Unit (Power), set the range unit oven toggle switch at ON and the emergency power switch at OFF.
    TO PLACE THE BELOW DECK PORTIONS OF RADAR EQUIPMENT MK 25 IN THE STANDBY CONDITION, proceed as follows:
Line Switch:
        a. Set the ship's radar power supply switch at ON. (When this is done, convenience outlets

in the radar unit cabinet, power supply cabinet, radar range unit, and radar transmitter-receiver will be energized, the heater circuit in the radar antenna and the range unit oven will be energized, and the dome lights in the radar transmitter-receiver unit will light if the dome light switch is at ON.)
    Radar Tracker (Automatic) (fig. 5) :
        a. Set the power switch at ON. (When this is done, the fuse indicator will light.)
Control Unit (Power) (fig. 6) :
a. Set the main switch at ON. (After this is done, the line voltage meter will read 115 ± 2 volts. The interlock lamp will light if the interlock circuit is closed.)
Controller (Antenna Motor) (fig. 4) :
        a. Set the power switch at ON.

2.3 THE PLOTTING ROOM

Stable Element Control Panel
The following operations should be performed at the stable element control panel (fig. 7) to place it in the standby condition:
        a. Set the mercury control switch at ON.
        b. Set the motor generator selector switch at the position corresponding to the generator that is to be used.
        c. Set the follow-up system switch at FILAMENTS AND LIGHTS ONLY.

        d. Determine when the gyro is up to speed by means of the gyro current switch and the gyro current ammeter. (When the gyro is up to speed, the ammeter should read approximately J..1 amps, for each phase.)
        e. After the gyro is up to speed, set the follow-up system switch at ON.
        f. Then set the mercury control switch at AUTO.

Stable Element
The following operations should be performed at the stable element (fig. 8):
        a. Set the latitude weight at the position corresponding to the ship's latitude.
        b. Set the firing selector switch at CONTINUOUS FIRE.
        c. Set the level follow-up switch at AUTO.
        d. Set the cross-level follow-up switch at AUTO.

Selector Drive
The following operations should be performed at the selector drive (fig. 9):
        a. Set the selector lever at CONNECT AND SYNCHRONIZE.
        b. Turn the hand crank until the zero reader dials are matched at the fixed index.
        c. Set the selector lever at LOCK.

Computer
The following operations are those required to place the computer in the standby condition.

Control Unit (fig. 10). Set:
        a. the generated bearing crank at the OUT position;
        b. the wind direction dial at the proper value;
        c. the wind speed dial at the proper value;
        d. the ship course hand crank at the OUT position;
        e. the ship course hand crank at the OUT
position, making sure that the ship speed dial synchronizes with the pitometer log repeater;
        f. the target angle hand crank selector at AUTO;
        g. the target speed switch at NORMAL;       
        h. the target speed hand crank selector at
AUTO;
        i. the control switch at AUTO;
        j. the range rate hand crank selector at AUTO;
        k. the generated range crank at the OUT position;
        1. the generated range dials at the value specified by doctrine and operating conditions:
       m. the range rate ratio or range time constant knob at the IN position;
       n. the range rate control switch at AUTO;
       o. the generated elevation crank at the OUT position;       
       p. the rate of climb hand crank at the IN (or MANUAL) position;
       q. the rate of climb dial at zero knots;
        r. the rate of climb hand crank at the OUT (or AUTO) position.
        s. By means of the target course slew push buttons and the target speed switch, slew target angle and target speed to the values established by doctrine according to the type of target expected.
        t. If Ordalt 2331 has been accomplished, set the AIR-SURFACE selector (fig. 28) at AIR.

Computer Unit (fig. 11). Set:
        a. the initial velocity dial(s) at the computed value of initial velocity;
        b. the dead time dial at the average value

of dead time for the gun mounts to be controlled ;
       c. the time motor switch at OFF;
       d. the power switch at ON. Indicator Unit (fig. 11). Set:
       a. the synchronize elevation hand crank at the IN position;
       b. the synchronize elevation dials together at the fixed index;
       c. the range spot hand crank at the OUT position, making sure that the range spot counter agrees with the range spot transmitter (fig. 18) ;
       d. the elevation spot knob at the OUT position, making sure that the elevation spot dial agrees with the spot transmitter (fig. 19) ;
       e. the deflection spot knob at the OUT position, making sure that deflection spot dial agrees with the spot transmitter (fig. 19) ;
       f. the sight angle hand crank at the OUT position;
       g. the fuze hand crank at the OUT position;
       h. the sight deflection hand crank at the OUT position;
       i. the star shell deflection spot dial (if any) at zero;
       j. the star shell elevation spot dial (if any) at zero;
       k. the star shell range spot dial at zero.

Since there are several stations in the gun director, the operating instructions are subdivided into the operations that should be performed at each of the following locations:
       Gun Director Pedestal.
       Radar Operator's Station.
       Pointer's Station.
       Trainer's Station.
       Assistant Control Officer's Station.
       Rangefinder Operator's Station.
       Control Officer's Station.

Gun Director Pedestal
       a. In Arma-control directors, set the line switches at the train, elevation, and cross-level controllers at ON, or:
       a'. In amplidyne-control directors, set the main disconnect switch at ON.
       b. Set the train parallax selector (if any) at AUTO.
       c. Set the elevation parallax selector (if any) at AUTO.

Radar Operator's Station
The steps outlined in this section assume that the radar equipments are being placed into operation from a cold start. Further, it is assumed that the radar room operations outlined in section 2.2 have been performed.

Radar Equipments Mk 12 and Mk 22 (fig. 12).
     RADAR EQUIPMENT MK 12.
        a. At the operator's control unit, set the pilot lamps switch at ON, the meter lamp switch at ON, and the power switch at ON.
        b. The pilot lamp just above the power switch should light, indicating that the filament transformers are energized. After about 1.5 minutes, the center pilot lamp should light, indicating that the time-delay relay has closed and that all door switches are properly closed. Do not proceed to the next step until the center pilot lamp is lighted.
        c. At the operator's control unit, set the STANDBY-OPERATE switch at OPERATE.
        d. At the indicator unit, set the selector switch at RANGE.
        e. At the transmitter-receiver unit, check the transmitter plate current. (It should be between 7 and 8 milliamperes.)
        f. At the indicator unit, adjust the focus and intensity controls to give a clear, sharply

defined sweep. (In order to preserve night vision, the intensity should be kept as low as possible for good operation.)
        g. At the operator's control unit, set the receiver sensitivity switch at AUTO. There should be approximately one-eighth inch of grass on the indicator unit screen.
        h. At the transmitter-receiver unit, adjust the receiver tuning control to give maximum signal. (To do this, bring a target pip* into the notch by means of the range hand crank on the range unit; set the receiver sensitivity switch at MAN to avoid saturation of pips while tuning; remove the cap protecting the receiver tuning control; and make the required adjustment.) Adjust the T-R tuning control for maximum signal.
        i. At the indicator unit, check the zero setting as follows: The receiver sensitivity switch at the operator's control unit should be at MAN and the adjacent gain control should be adjusted until the height of the transmitted pulse is approximately one-half inch. Center the transmitted pulse in the notch and check that the range reading is within 10 yards of the zero-setting range.
        j. Set the receiver sensitivity switch at AUTO.
        k. At the range unit, set the range dials according to doctrine for the operating conditions and most probable target.

RADAR EQUIPMENT MK 22.
        a. Check to see that the Radar Equipment Mk 12 is in complete operation. Be sure that the set is pulsing. ATTEMPTING TO OPERATE RADAR EQUIPMENT MK 22 WITHOUT HAVING THE MAIN RADAR EQUIPMENT (MK 12) IN FULL OPERATION WILL RESULT IN SERIOUS DAMAGE TO THE MK 22.
        b. At the amplifier power assembly, depress the ON button of the 400-cycle power switch. The indicating lamp above the 400-cycle power switch, as well as the meter lamps, should light. The dimmer control adjusts the intensity of these lamps.
        c. Check to see that the pointer turns the intensity control on his indicator unit (fig.14) counterclockwise to reduce the spot intensity and prevent damage to the screen.
        d. Perform the following checks:
            (1) Make sure that the two blowers in the amplifier-power assembly are operating.
            (2) Place the test meter switch at the CONV MA position to observe crystal current. (This should not exceed 0.8 milliampere.)
            (3) Place the test meter switch at REG RECT+VX100 position. Regulated rectifier voltage should be between 290 and 310 volts.
            (4) Place the test meter switch at the REG RECT-VX200 position. (The negative output voltage of the regulated rectifier should be between 360 and 390 volts.)
        e. Check again to be sure that the transmitter of the main radar is operating. At least 1 minute must elapse between the time the 400-cycle power switch is depressed and step (f).
        f. Press the OPERATE button of the transmitter switch.
        g. Observe the magnetron current on the test meter (test meter switch at the MAG MA X 5 position). Magnetron current should be between 2.7 and 3.3 milliamperes. The pilot lamp above the transmitter switch should light.
        h. Check to make sure that the 400-cycle voltage meter reads 115 volts.
        i. Set the indication switch at the MAN position. Mk 22 performance can now be checked on the main radar's range oscilloscope.
        j. Reduce the receiver gain of the main radar so that only Mk 22 signals appear on the oscilloscope screen. On main radars with automatic gain control, the receiver sensitivity switch should be placed on the MAN position for this adjustment.
        k. Point the antenna toward a fixed target if one is available. Otherwise, use the strongest moving target available. If no target is available, use the transmitted pulse in making the next adjustment.
        1. Adjust the REG GAIN control on the indicator unit (fig. 14) until the target echo signal can be seen clearly. It must be kept below saturation at all times.
        m. With the RECEIVER TUNE switch in the MAN position, tune the receiver for maximum echo response. The repeller voltage setting should be noted and recorded for future

*If a target is not available, the tuning adjustment may be made by using the test unit of Radar Equipment Mk 12.

reference. This setting should be maintained when automatic frequency control is used because of the interaction between the two circuits.
        n. Set the receiver tune switch at AFC. If the repeller voltage is different from the value recorded in step (m), adjust the receiver tune adjustment control to make the voltage equal the recorded value.
        o. Set the antenna drive switch at ON. Check to see that the antenna oscillates.
        p. Set the REG GAIN control (fig. 14) at REMOTE, and the indication switch (fig. 12) at NORM.

Radar Equipment Mk 25.
        a. At the radar transmitter-receiver, set the wave guide switch handle at the UNLOCKED position and the RADAR-COMM toggle switch at RADAR.
        b. At the Radar Console Mk 5 (fig. 13) :
          (1) Set the wave guide selector at ANTENNA ONLY.
          (2) Set the MOD SELECTOR switch at LOG.
          (3) Set the ANTIJAM selector at OFF.
          (4) Set the RECEIVER CONTROL selector at AFC.
          (5) Set the GAIN selector at AGC.
          (6) Set the COMPUTER AID switch at ON.
        c. If one-man (trainer) control is desired, set the TRAINER CONTROL switch of the radar console at ON.
        c'. If three-man control (trainer, pointer, radar operator) is desired, continue as follows at the Radar Console Mk 5:
          (1) Press the OPERATE push button. The OPERATE lamp should light after about 3 minutes.
          (2)Set the VIDEO SELECT switch at OPR.
          (3) Set the SWEEP selector at PRES.
          (4) Adjust the Radar Indicator Mk 21 DIMMER control until the horizontal and vertical indexes on the indicator are easily visible.
          (5) Set the DISPLAY selector at B.
          (6) Push the HORIZ CENTER knob and adjust it so that the range sweep is coincident with the vertical index.
          (7) Set the DISPLAY selector at E.
          (8) Push the VERT CENTER knob and adjust it so that the range sweep is coincident with the horizontal index.
          (9) Set the SWEEP selector at MAIN.
          (10) Adjust the Radar Indicator Mk 20

MAIN RANGE POSITION knob so that the start of the sweep is one-fourth inch from the left edge of the indicator screen.
          (11) Adjust the Radar Indicator Mk 21 MAIN RANGE POSITION knob so that the sweep starts one-fourth inch from the left edge of the indicator screen.
          (12) Adjust the DIMMER control until the range dials and designated range indicators are visible.
           doctrine to suit the operating conditions, possible target, etc.
          (14) The READY light on the indicator display should be extinguished. If not, extinguish the light by stepping on the radar operator's automatic-manual transfer foot switch.

Pointer's Station (fig. 14)
        a. Turn the port cover handwheel to open the cover over the pointer's telescope.
        b. Set the elevation selector lever at LOCAL.
        c. Press the ON push button.
        d. Set the elevation selector lever at AUTO.
        e. Adjust the telescope filter control knob and illumination control knob to suit the operating conditions.
        f. Set the telescope diopter adjustment to suit the pointer.
        g. If equipped with Radar Equipments Mk 12 and Mk 22:
          (1) Set the indicator unit (Radar Equipment Mk 12) selector at ELEV.
          (2) Adjust the focus and intensity controls to give a clear, sharply denned trace.
          (3) Check that the antenna of Radar Equipment Mk 22 is oscillating.
          (4) At the indicator unit (Radar Equipment Mk 22) : turn the REC-GAIN control fully counterclockwise. Adjust the intensity control until a vertically moving spot is just perceptible. Adjust the SWP-AMP control, if necessary, so that the sweep moves between the top and bottom of the screen. Center the screen presentation horizontally by adjusting the H-CNTR control. Turn the REC-GAIN control clockwise until the spot intensity is increased to a point where a dim vertical line is continuously visible over the entire height of the screen.

        g'. If equipped with Radar Equipment Mk 25 (fig. 15) :
          (1) Adjust the DIMMER controls until the indexes on both screens are visible.
          (2) Have the radar operator (or trainer) set the SWEEP selector at PRES.
          (3) Set the DISPLAY selectors at E.
          ident with the horizontal indexes on both indicators.
          (5) Set the DISPLAY selectors at B.
          (6) Push the HORIZ CENTER knobs and adjust them so that the range sweep on both indicators are coincident with the vertical indexes.
          (7) Have the radar operator (or trainer) set the SWEEP selector at MAIN.
          (8) Adjust the MAIN RANGE POSITION knobs until both range sweeps start one-fourth inch above the bottom edges of the indicator screens.
          (9) Set the Radar Indicator Mk 22 DISPLAY selector at AE.
          (10) Extinguish the READY lights on both indicators by operating the trainer's and pointer's automatic-manual foot switches (Transfer Switch Mk 13).

Trainer's Station (fig. 16)
        a. Turn the port cover handwheel to open the cover over the trainer's telescope.
        b. Withdraw the train locking pin by turning the knob counterclockwise until the limit is reached.
        c. Set the train locking pin switch at ON.
        d. In Arma-control directors, set the train selector at LOCAL.
        d'. In amplidyne-control directors, set the train selector at MANUAL.
        e. Press the train ON push button.
        f. Set the train selector at AUTO.
        g. Adjust the telescope filter control knob and illumination control knob to suit operating conditions.
        h. Set the telescope diopter adjustment to suit the trainer.
        i. If equipped with Radar Equipment Mk 12:

          (1) Set the indicator unit (Radar Equipment Mk 12) selector at TRAIN.
          (2) Adjust the focus and intensity controls to give a clear, sharply denned trace.
        i'. If equipped with Radar Equipment Mk 25 (fig. 15) :
          (1) Set the antenna scan selector at AUTO.
          (2) IF ONE-MAN CONTROL IS DESIRED, press the OPERATE push button; set the SWEEP selector at MAIN; and by means of the range SLEW lever, set range at the value prescribed by the ship's doctrine to suit operating conditions, possible targets, etc.

Assistant Control Officer's Station (fig. 17)
        a. Set the power transfer switch at NOR.
        b. Withdraw the cross-level zero locking pin (fig. 18).
        c. Lift the cross-level reset handwheel to disengage it from the cross-level gearing.
        d. Set the cross-level reset switch at ON.
        e. In Arma-control directors:
          (1) Set the cross-level zero lock switch at ON (fig. 18).
          (2) Press the cross-level ON push button.
        e'. In amplidyne-control directors:
          (1) Press the cross-level ON push button. (In some amplidyne-control directors, the push button is labeled START.)
          (2) Set the cross-level zero lock switch at ON (fig. 18).
        f. Set the star shell range spot dials at zero.
        g. Set the star shell elevation spot dials at zero.
        h. Set the star shell deflection spot dial at zero.
        i. Set the searchlight control handle at OFF-CLOSE.
        j. Set the searchlight elevation offset dial at zero.
        k. Set the searchlight deflection offset dial at zero.
        1. Open the overhead hatch cover if desirable.
        m. Set the target designation selector switch (if any) for the desired target designation center.
        n. At the Identification Indicator (fig. 18), set the challenge switch at OFF; the IFF gain control knob at the extreme counterclockwise position; the calibrate switch at OFF; and the power switch at OFF.

        o. At the BN-1 (or BN) unit, set the gating switch at OFF; the keyer switch at ON; and the power switch at ON.
        p. At the Identification Indicator (fig. 18) set the power switch at ON.
        q. Set the IFF challenge switch (fig. 18) according to doctrine and operating conditions.

Rangefinder Operator's Station (fig. 18)
        a. Set the change of range receiver switch at ON.
        b. Set the range spot dials at zero.
        c. Set the range selector switch at RADAR & AR to R.F.
        d. Set the rangefinder elevation offset scale at zero.
        e. Remove the protective caps from the ends of the rangefinder.
        f. Make the following adjustments to the rangefinder in the order listed:
          (1) interocular adjustment,
          (2) diopter adjustments,
          (3) height adjustment,
          (4) internal correction adjustment.
        g. Adjust the illumination controls, the filter control knob, and the searchlight filter knob to suit operating conditions.
        h. By means of the range knob, set range at the stand-by value as prescribed by doctrine.

Control Officer's Station (fig. 19)
        a. On amplidyne-control directors, set the slewing sight train securing pin and the elevation selector at SLEW.
        a'. On Arma-control directors, unlock the slewing sight.

        b. Press the slewing key.
        c. Slew to the stand-by position as determined by the ship's doctrine.
        d. Set the interocular and diopter adjustments of the binocular to suit the control officer.
        e. Set the elevation spot dials at zero.
        f. Set the deflection spot dials at zero.
        g. Set the battle telephone selector switch at 5JP (air defense circuit).
        h. If equipped with Radar Equipment Mk 12:
          (1) Set the indicator unit selector (Radar Equipment Mk 12) at SPOT.
          (2) Adjust the focus and intensity controls to give a clear, sharply denned trace.
        h'. If equipped with Radar Equipment Mk 25 (fig. 20) :
          (1) Set the DIMMER control so that the horizontal and vertical indicator screen indexes are visible. Have the radar operator (or trainer) set the SWEEP selector at PRES.
          (2) Set the DISPLAY selector at E.
          (3) Push the VERT CENTER knob and adjust it so that the range sweep coincides with the horizontal index.
          (4) Set the DISPLAY selector at B.
          (5) Push the HORIZ CENTER knob and adjust it so that the range sweep coincides with the vertical index.          
          (6) Have the radar operator (or trainer) set the SWEEP selector at MAIN.
          (7) Adjust the MAIN RANGE POSITION knob so that the sweep starts one-fourth inch above the lower edge of the indicator screen.

Figure 20. Control Officer's Station—Gun Director
Mk 37 (Equipped with Radar Equipment
Mk25).

Gun Fire Control Systems Mk 37 are used to control a variety of guns, mounts, and turrets. The following description of operations that must be performed at the gun mount (or turret) is necessarily general. Specific instructions for performing the operations outlined below can be found in the OP applying to the type of gun mount (or turret) in question. The applicable OP's are as follows:
       
       Mount (or turret)                     OP
            5"/38 D.P. (single) ................ 735
            5"/38 D.P. (twin) .................. 805
            5"/54 D.P. (single) ...............1027
            5"/54 D.P. (twin) .................1527
            6"/47 D.P. (twin) .................. 760
            6"/47         (triple) ................. 833
            8"/55 D.P. (triple) ................1180

Controller Line Switches
        a. Set the controller line switches, located at the train and elevation power motor controllers, at ON.

Gun Captain's Station
        a. Set all selector switches at the position which permits control by the Gun Fire Control System Mk 37.

Gun Train Drive
        a. Start the train drive power motor.
        b. Set the selector at AUTO.
        c. Set the parallax selector (if any) at AUTO.

Gun Elevation Drive
        a. Start the elevation drive power motor.
        b. Set the selector at AUTO.
        c. Set the parallax selector (if any) at AUTO.

Fuze Setter
        a. Start the fuze setter.
        b. Set the selector at AUTO.

The operations outlined in sections 2.1 to 2.5 place the Gun Fire Control System Mk 37 in the stand-by condition. This section briefly summarizes the status of the gun director and the plotting room equipments when in the stand-by condition.

Gun director. The gun director is completely energized. Cross level and the parallax corrections are being received automatically. The computer aid circuits are so connected that the generated quantities will be received from the computer at the train and elevation drives, the range finder, and the radar range unit. The radar equipment is energized and radiating so that it may be utilized as search equipment during the stand-by period. Only a few switching operations are required in shifting to the tracking phase; no waiting period is necessary. The gun director complement consists of six men when fully manned. When equipped with Radar Equipment Mk 25 Mod 2, the gun director may be placed in the stand-by condition with only one operator, the director trainer.

Plotting room. The stable element is energized and in automatic control, continuously transmitting level and cross level to the computer, cross level to the gun director, and level to the searchlights (in certain installations only).

Except for the time motor, the computer is completely energized and in automatic control. The sensitivity of Computers Mk 1A is at its maximum value. To commence tracking it is only necessary to introduce estimated values of target speed and target course (or target angle), and energize the time motor.

In addition to transmitting parallax, fuze setting, and gun orders, the computer is set up for transmitting generated quantities to the gun director to aid in the tracking problem.

Introduction
Gun Fire Control System Mk 37 is designed primarily for use against air targets, both visible and obscured. Since the procedures to be followed for engaging these two types of air target differ in several respects, they will be discussed separately. The instructions assume that the equipments have been placed in the stand-by condition as described in chapter 2.

The problem of engaging a target can be divided into three phases: (1) target acquisition, (2) tracking, and (3) firing.

The first phase, target acquisition, commences when a target is designated to the director. It ends when the target is centered in the director scopes and the director control officer informs plot that the gun director is "ON TARGET."

The second phase, tracking, is the time that the director stays "ON TARGET." The fire control problem is solved during this phase. The third phase, firing, is started by the "COMMENCE FIRING" order and ended by the "CEASE FIRING" order. Operations of the tracking phase are continued during this phase.

3.1 VISIBLE AIR TARGETS (WITH RADAR EQUIPMENT MK 12)

This section outlines the method of engaging visible air targets for systems equipped with Radar Equipment Mk 12. The procedure for systems equipped with Radar Equipment Mk 25 is given in section 3.3.

Since most air targets that are visible at the time of initiating action against them are undesirably close, the quickest and most direct method of engaging them must be employed. Figure 21 indicates the over-all function of the major units of the Gun Fire Control System Mk 37 when it is equipped with Radar Equipment Mk 12 and employed against a visible air target. The most effective method of operating a system so equipped, utilizes optical tracking in train and elevation, and radar tracking in range. The optical range finder is used for designation and identification purposes, serving to designate the proper target pip to the radar operator by giving him an approximate range, and helping in the identification problem by visual recognition when the IFF response is not conclusive. As indicated by figure 21, the stable element furnishes stabilization data to the computer. From the target position data, received from the gun director, and the stabilization data, the computer determines the required fuze setting and gun position data. Firing of the guns is controlled from the gun director. A detailed outline of the target acquisition, tracking, and firing operations follows.

Target Acquisition
On a well-organized and trained ship, the air defense station should play an active part in target acquisition by designating visible targets. Information as to the target's position and other characteristics should be relayed to the proper gun director. Since the range of a visible target is probably short, target acquisition must be accomplished by the most direct method in order to allow sufficient time to engage the target before the target accomplishes its mission.

Gun director.

The following operations should be performed at the gun director during the acquisition of a visible target:

AT THE CONTROL OFFICER'S STATION (fig. 22) :
        a. Press the slewing key and offset the slewing sight in the direction of the target. This causes the gun director to slew toward the target.
        b. Continue to slew the gun director until the target is centered in the slewing sight. (Practice, more than anything else, is

required for the control officer to be able to put the director sights on the target in a minimum time.)

        c. Keep the target centered as well as possible in the slewing sight, give the word "ON TARGET" to plot, and close the slewing sight rate control key. When the rate control key is closed, circuits are completed which drive the computer towards the correct solution. (NOTE: Ordalt 2840 provides the slewing sight rate control key.)
AT THE RADAR OPERATOR'S STATION (fig. 23) :

Figure 23. Radar Operator's Station—Gun Director
Mk 37 (Equipped with Radar Equipments
Mk 12 and Mk 22).

Figure 24. Rangefinder Operator's Station—Gun Director Mk 37.

Tracking
Tracking commences when the director control officer gives the word "ON TARGET" and continues until the target is destroyed or passes out of range. During this period the following operations should be performed.

Gun Director.
AT THE CONTROL OFFICER'S STATION (fig. 22) :
        a. After the slewing sight has been held on the target for a few seconds with the rate control key closed in order to establish approximately correct rates at the computer, release the rate control key and the slewing key, thereby transferring control of the gun director to the pointer and trainer.

AT THE POINTER'S STATION (fig. 25) :
        a. Turn the pointer's handwheels until the horizontal cross hair of the pointer's telescope is on the target. If necessary, continue turning the handwheels to keep the horizontal cross hair on the target as much of the time as possible.
        b. Whenever the horizontal cross hair of the pointer's telescope is on the target, press the pointer's rate control key. (After considerable practice, the pointer and trainer should acquire a "feel" of the system which will tell them how closely the target should be centered in their telescopes before they close their rate control keys. See the discussion of solution time constants later in this section.)

AT THE TRAINER'S STATION (fig. 26) :
        a. Turn the trainer's handwheels until the vertical cross hair of the trainer's telescope is on the target. If necessary, continue turning the handwheels to keep the vertical cross hair on the target as much of the time as possible.
        b. Whenever the vertical cross hair is on the target, press the trainer's rate control key.

AT THE RADAR OPERATOR'S STATION (fig. 23) :
        a. Keep the target pip in the notch of the indicator unit screen.
        b. Hold the rate control switch ON whenever the target pip is in the notch.

Figure 26. Trainer's Station — Gun Director Mk 37 (Equipped with Radar Equipment Mk 12).

AT THE RANGE FINDER OPERATOR'S STATION (fig. 24) :
        a. Observe the target through the range finder and give the plotting room estimates of target angle.
        b. Continue to assist with the designation and identification problem if necessary.
        c. Range on the target so that a stand-by range is available in case the radar equipment loses the target.

Plotting Room.
AT THE COMPUTER (fig. 27) :
        a. By means of the target course slew buttons, slew target angle to the value estimated at the gun director or air defense station.
        b. When the director control officer gives the word "ON TARGET," set the time motor switch at ON.
        c. If Ordalt 2331 has not been accomplished, set the range rate ratio knob at the lowest value possible without causing target
speed and target angle to oscillate. This gives a minimum range solution time constant without causing instability. Time constants are discussed in more detail in the Evaluation of Method part of this section.
        c'. If Ordalt 2331A has been accomplished (fig. 28) :
            (1) Set the range time constant knob at 2 seconds.
            (2) If the target maneuvers radically (i.e., the solution indicators spin), momentarily depress the sensitivity push button. This increases the computer sensitivity as explained later in this section.

Gun Mount.
    AT THE POINTER'S STATION :
        a. Close and lock the pointer's firing key.

Firing
Firing starts when the "COMMENCE FIRING" order is given. The following operations

Figure 30. Effect of Sensitivity Push Button on Time Constant.

This section outlines the operation of Gun Fire Control System Mk 37 (equipped with Radar Equipments Mk 12 and Mk 22) when engaging obscured targets. The term "obscured targets" applies to night attacks and to daytime attacks when the target is initially obscured. Many present-day, and probably a greater proportion of future, air targets come under this classification because, even though attacking by day, they are, when detected, beyond the average range of visibility in prevailing cloud conditions, etc. The operating procedure for engaging obscured air targets when using a system equipped with Radar Equipment Mk 25 is given in section 3.3.

Figure 31 indicates the functions performed by various units when engaging an obscured air target. It can be seen that the fire control radar equipment furnishes all of the target position data. Since with Radar Equipments Mk 12 and Mk 22 this data is not very smooth, the

computer is operated in semiautomatic in order to increase the solution time (reduce the computer sensitivity) so that irregularities in the target position data will not affect the computer solution. In semiautomatic operation, the generated and observed bearing and elevation are matched manually instead of automatically, permitting the computer operators to control the computer sensitivity.

Target Acquisition

For acquisition of obscured targets, the Gun Fire Control System Mk 37 must depend principally on information from sources outside the system. These sources include the ship's search radars, information received via AA coordination circuits or other channels, A.E.W. etc. The information which these sources provide is collected, evaluated, and used as the basis for originating target designations in the target designation center, a central below-decks location. When targets are located and are to be designated to the Gun Fire Control System Mk 37, the range and bearing, and in some cases elevation, of these targets is required to be
transmitted to the gun director along with other information such as the number of targets, the possibility of friendly aircraft in the same area, target course, etc. The range, bearing, and elevation designations may be transmitted via synchro indicating systems or by phone concurrently with other information.

Gun Director.
The following operations should be performed at the gun director during the acquisition of an obscured target.

AT THE CONTROL OFFICER'S STATION (fig. 22) :
        a. Press the slewing key and slew the director until the bearing indicator indicates the designated bearing.

AT THE POINTER'S STATION (fig. 25) :
        a. Turn the pointer's handwheels until the director elevation ring dial of the elevation indicator is matched with the inner target designation pointer.
        b. Conduct a search until the target pips on the display screen of the indicator unit (Mk 12) are matched. Some definite plan of search should be established, depending on the accuracy of the designation data and the type of

radar equipment being used. A possible method when no designation is available, is to have the trainer train to one end of his sector. The pointer should elevate to about 80 degrees. Then the trainer should train 10 degrees from the end of the sector. The pointer should depress to zero degrees, and so forth until the sector is covered.
        c. When the radar operator puts the target pip in the notch of his indicator unit, set the pointer's indicator unit (Mk 12) selector at SPOT and keep the target pip aligned with the horizontal crossline. (The elevation meter may be used instead of the indicator unit if desired.)        
        d. When the target pip is on the horizontal cross line (or the elevation meter needle is not deflected), press the pointer's rate control key.
        e. If the position angle of the target is below 15 degrees, use the indicator unit (Mk 22) because it will give more accurate data than the Mk 12 equipment at low angles. Turn the pointer's handwheels until the target pip is bisected by the horizontal marker sweep.

AT THE TRAINER'S STATION (fig. 26) :
        a. Turn the trainer's handwheels until the director train (or target bearing) ring dial of the train indicator is aligned with the inner target designation pointer.        
        b. Train the director back and forth until the target pips on the display screen of the indicator unit are matched.         c. After the radar operator puts the target pip in the notch of his indicator unit, set the trainer's indicator unit (Mk 12) selector at SPOT and train the director to keep the target pip aligned with the vertical cross line. (The train meter may be used instead of the indicator unit if desired.)         
        d. When the target pip is on the vertical cross line, press the trainer's rate control key.

AT THE RADAR OPERATOR'S STATION (fig. 23) :
        a. On the range unit, turn the range handcrank until the pointers of the range indicator are matched, then center the designated target pip in the notch of the indicator unit screen.
        b. If there are several targets on the screen, gate the one at the shortest range. Then check with the assistant control officer to see if it is a "friendly" or a "bogey." If it turns out to be a friendly (i.e., gives the proper IFF response), gate the next shortest range target. Continue this process until the bogies are located.
        c. Relay any useful information obtained on targets to the target designation center.
        d. Set the auto switch at ON.
        e. Hold the rate control switch ON whenever the target pip is in the notch.
        f. Set the computer aid switch at ON.

AT THE ASSISTANT CONTROL OFFICER'S STATION :
        a. Set the identification indicator (fig. 24) challenge switch at ON.
        b. Observe the screen of the identification indicator and inform the control officer whether the target being tracked is a "friendly" or a "bogey." Tracking Gun Director.

AT THE POINTER'S STATION (fig. 25) :
        a. Turn the pointer's handwheels to keep the target pip aligned with the horizontal cross line of the indicator unit (Mk 12). (If the indicator unit (Mk 22) is used, keep the target pip bisected by the horizontal marker sweep.)
        b. Keep the pointer's rate-control key closed when the above condition exists.

AT THE TRAINER'S STATION (fig. 26) :
        a. Turn the trainer's handwheels to keep the target pip aligned with the vertical cross line of the indicator unit.
        b. Keep the trainer's rate control key closed when the above condition exists.

AT THE RADAR OPERATOR'S STATION (fig. 23) :
        a. Keep the rate control switch at ON when the target pip is gated. Plotting Room.

AT THE COMPUTER (fig. 27) :
        a. Set the control switch at SEMI-AUTO.
        b. Set the generated bearing and generated elevation cranks at the IN position.

        c. Slew target angle to the proper quadrant. The proper quadrant may be determined by observing the relative bearing and observed range dials.
        d. Set the time motor switch at ON.
        e. By means of the generated bearing crank, make the generated bearing dial turn at the same rate as the relative bearing ring dial whenever the dh-ector trainer's signal indicates that he is "on target."
        f. By means of the generated elevation crank', make the generated elevation dial turn at the same rate as the elevation ring dial whenever the director pointer's signal indicates that he is "on target."
        g. Set the range rate ratio (or range time constant) knob on as low a value as possible without causing target speed and target angle to oscillate. (See the discussion of solution time constants in the preceding section.)
Gun Mount.
    AT THE POINTER'S STATION :
        a. Close and lock the pointer's firing key.

Firing
The procedure for firing at obscured targets is identical with that for visible targets except that the slow semiautomatic solution may make it possible to spot. Spotting against a target obscured by darkness is possible when using MTF ammunition by having the control officer spot the bursts in deflection and elevation until they are centered in the pointer's optical telescope. Range spotting is possible if the bursts can be seen on the radar operator's type A presentation (see fig. 40). If during the engagement of an obscured target, the target becomes visible, it is advisable in gun directors equipped with Radar Equipments Mk 12 and Mk 22 for the director pointer and trainer to shift to the more accurate and smoother optical tracking. However, before making the shift, care should be taken to ascertain that the visible target is the target that is being tracked by the radar equipment.

Evaluation of Method
Although full automatic is by far the best method of operating a gun fire control system, target position data obtained with Radar Equipments Mk 12 and Mk 22 are not continuous enough to warrant automatic bearing and elevation rate control. In semiautomatic control the target's path is computed by averaging observations over a rather long period. Obviously for a maneuvering target, this procedure is not good. However, with Radar Equipments Mk 12 and Mk 22 it is the best that can be used against obscured air targets.

3.3 OPERATION WITH RADAR EQUIPMENT MK 25

Radar Equipment Mk 25 is an automatic-tracking fire control radar. Since the operation of certain parts of the gun director is different when this equipment is used, this section will describe the differences. Operation of equipments not mentioned in this section is unchanged by the addition of Radar Equipment Mk 25. Except for the target acquisition phase there is no difference between operation of the gun director against visible air targets and operation against obscured air targets; therefore the operating instructions for these types of targets are combined. With Radar Equipment Mk 25 installed, it is possible to operate the gun director with one man, the trainer. This type of operation is described later in this section.
When used against obscured targets, the major units of the system function as shown in figure 31, the fire control radar supplying all of the target position data. Figure 32 shows the disposition of the equipments when engaging visible air targets. It is evident from these figures that the only differences in operation exist in the target acquisition phase.

Target Acquisition
The procedure to be followed for acquiring visible targets is the same as that outlined in section 3.1. The procedure for obscured targets follows:
     AT THE POINTER'S AND TRAINER'S STATIONS (fig. 33) :
        a. If a bearing designation is available, turn the trainer's handwheel until the gun director is at the designated bearing. Elevate the director by means of the pointer's handwheels until the target is located on Δ E presentation

of the Radar Indicator Mk 22. Since this indicator has a long persistence screen, it is necessary only to pass by the target to have it appear on the screen. (When the delta E presentation is being used, the display is moved vertically across the screen by an elevation signal from the computer. This has the effect of stabilizing the scope presentation and enables the pointer to pass by a target and then determine its position angle from the scale at the sides of the display.)
        a'. If no designations are available, train to one end of the designated sector of coverage. Then have the pointer elevate to 90 degrees, observing the Δ E presentation of the Radar Indicator Mk 22 for the target pip. If no target is located, train 10 degrees from the end of the sector. Then have the pointer depress to zero. Continue this search plan until the pointer locates the target on his Δ E presentation.
        b. Set the Radar Indicator Mk 22 DISPLAY selector at E. This type of display indicates range horizontally and elevation vertically.

     AT THE RADAR OPERATOR'S STATION (fig. 34):
        a. If under attack, press the BATTLE SHORT push button. This shorts all interlocks and prevents unintentional interruptions. The battle short lamp should light.
        b. If a range designation is available, match the RANGE dials with the DESIGNATED RANGE dial by means of the RANGE SLEW lever. When the designated range and range dials are matched, the designated range indexes will cross on the vertical marker. Locate the target pip by observing the type A presentation in the vicinity of the range marker. When the target pip is located, put it in the notch of the range sweep by means of the RANGE SLEW lever.
        b'. If a range designation is not available, search for the target pip on the type A presentation. When it is located, put the target pip in the notch by means of the RANGE SLEW lever.

Manual Tracking with Radar Equipment Mk 25
In the event of a casualty to the automatic tracking equipment, indicated by the TRACK light (figs. 33 and 34) flickering or failing to light, the pointer, trainer, or radar operator may track the target munually. When this is done the corresponding rate-control key or push button (figs. 33 and 34)should be closed.

Visible Surface Targets
There are two ways of employing the Gun Fire Control System Mk 37 against visible surface targets, either of which may be used without appreciable sacrifice of effectiveness. Both methods are described in this chapter, together with their advantages and disadvantages. The choice of method depends on which of the advantages it is desirable to stress in any given situation.

Method 1. Figure 35 shows the function of the elements of the Gun Fire Control System Mk 37 when using this method to engage a visible surface target. The over-all operation of the system is almost identical with that used (fig. 21) to engage visible air targets, the only differences being in the operation of the computer.

     AT THE COMPUTER (fig. 36) :
        a. Set the fuze hand crank at the IN position. This de-energizes the fuze servo motor and permits fuze setting order to be set as indicated below in (b).
        b. By means of the fuze hand crank, set the fuze counter at:
                  1. 55 seconds for 5"/38 computers,
                  2. 49 seconds for 5"/54, 6"/47, and 8"/55 computers.
Since the fuze setter at the mount (or turret) is left in automatic, this sets the mechanical time fuze of A A common projectiles on SAFE. (NOTE: The upper fuze limit on certain 5"/38 computers is 45 seconds. On these

computers, the fuze must be set manually on SAFE at the gun mount.)
        c. Set the rate of climb handcrank at the IN (or HAND) position. This engages the hand-crank and, on later models, de-energizes the rate of climb servo motor, permitting manual settings of rate of climb.
        d. By means of the rate of climb hand-crank, set the rate of climb dial at zero knots, the correct value for surface targets.
        e. On computers that have not been modified to include the target vector type of rate control (this modification is Ordalt 2331A), use manual rate control. The procedure for manual rate control is given in a subsequent part of this chapter.
        e'. On computers that have had Ordalt 2331A accomplished, set the AIR-SURFACE selector (fig. 28) at SURFACE, and set the surface time constant control transmitter in accordance with existing instructions (NOTE: Current instruction (Jan. 1949) direct that the time constant control transmitter dial be set at 3.). If shortly after getting "on target," the solution indicators spin, press the sensitivity push button. This quickly corrects any error in the original computer set-up.
        f. 5"/54 computers only—When range is above 20,000 yards, turn the elevation spot knob until the range graduation corresponding to present range is matched with the fixed index for the elevation spot dial. This procedure permits the computer to be used at ranges above the upper limit of advance range.
It should be noted that this method of fire requires the director pointer to keep the horizontal cross hair of his telescope on the target's water line. Although this procedure makes the range dispersion of the system largely dependent on the accuracy with which the director pointer tracks the target, it has the following advantages:
        a. Positional errors in the level angle as determined by the stable element do not materially affect the computed gun elevation order.
        b. The elevation angle in the computer is at its proper value (instead of at zero degrees) thereby allowing a correct solution of the prediction problem.
        c. No change in the position of the synchronize elevation hand crank is required when shifting to air targets.

Method 2.
This method utilizes the Gun Fire Control System Mk 37 as shown in figure 37.

In this method, elevation data is obtained from the stable element instead of from the gun director. An advantage of this method is that it replaces a human (the director pointer) with a mechanism, thereby reducing the probability of personnel errors, and it usually gives a smaller dispersion in range, which is sometimes desirable. This method MUST be used when the large circle scan of Radar Equipment Mk 25 is being used for spotting purposes because the director pointer must elevate some 5 degrees above the target so that the trainer may get a type B presentation for deflection spotting. If the computer dip dials (fig. 36) are calibrated for the mean trunnion height that exists on the ship, the effectiveness of method 2 is not materially different from the effectiveness of method 1.
The procedure for method 2 is identical with method 1 except for the following additional steps at the computer (fig. 36).
        a. Set the synchronize elevation hand crank at the CENTER position and turn it until the elevation dial is at zero. Then set the synchronize elevation hand crank at the OUT position and match the dip dials with the advance range counter.

Obscured Surface Targets
The recommended procedure for engaging obscured surface targets is the same as method 2 for visible surface targets except that the target should be tracked as outlined in section 3.2 (sec. 3.3 if Radar Equipment Mk 25 is installed).

Surface Spotting (with Radar Equipment Mk 25)
Accurate range and deflection spots for either visible or obscured surface targets may be obtained from Radar Equipment Mk 25 by utilizing it as outlined in this section. These operations are in addition to those previously outlined in section 3.3 for target acquisition and tracking. Method 2 for engaging surface targets must be employed with this procedure because the director pointer does not stay "on target."
     AT THE RADAK OPERATOR'S STATION (fig. 38):

5 degrees so that the lower part of the circle-scan annular ring intersects the target. Do not close the pointer's rate control key.

     AT THE CONTROL OFFICER'S STATION :
        a. Obtain the required deflection spot by estimating the distance between the splash (or mean splash of a salvo and the target on the type B presentation of the Radar Indicator Mk 21 (fig. 20).
        b. Apply the spot estimated in (a) at the deflection spot knob of the Spot Transmitter (fig.22). AT THE RADAR

OPERATOR'S STATION :
        a. Obtain the required range spot by estimating the distance between the splash (or mean splash of a salvo) and the target on the type A presentation (fig. 34) of the Radar Indicator Mk 20.
        b. Apply the spot obtained in (a) by means of the range spot knob of the Range Spot Transmitter (fig. 24).

Estimating spots.
To illustrate estimation of required range and deflection spots from Radar Equipment Mk 25 screen presentations, two rather exaggerated problems are presented. Figure 39 illustrates a two-gun salvo. One splash is an "over" and one is a "short." In the upper left portion of the figure is the corresponding type A presentation. The target pip is in the notch and the two splash pips are on opposite

sides of the target. Since it is known that on precision (PRES) sweep, the range sweep is 4,000 yards long, the distance between the splashes and the target may be easily estimated. In this case, the splash on the left represents a "short" of 400 yards and would require an ADD spot of 400 yards, while the splash on the right would require a DROP spot of 400 yards. The type B and type E presentations corresponding to the problem in figure 39 are shown at the bottom of the figure. The type B presentation indicates that the short splash would require a RIGHT deflection spot, while the long range splash would require a LEFT deflection spot. The magnitude of the required deflection spot may be estimated if it is remembered that, when using circle scan, the field of coverage is 12 degrees wide; hence a splash pip half way between the target pip and the left edge of the type B scan would require a 3-degree or approximately 50 mils RIGHT deflection spot. Thus it can be seen from the type B presentation in figure 39, that the short splash requires a RIGHT deflection spot of approximately 20 mils while the long range splash requires a LEFT deflection spot of approximately 20 mils.

The types A, B, and E presentations showing the splashes of a typical 6-gun salvo are shown in figure 40. Since the mean point of impact (M.P.I.) should be spotted to the target, good spots for this situation would be ADD 300 yards and RIGHT 30 mils.

Time Constants for Surface Fire

Since effective spotting is possible against surface targets, it is important that the gun fire control system have a stable solution so that there will be little dispersion between successive salvos. If the system time constant were left the same as for air targets (fig. 29), each small perturbation in director train would cause a change in the target setup at the counter. This in turn would cause the gun mounts (or turrets) to move, resulting in an unpredictable pattern that would be impossible to spot. For this reason, the system time constant is increased for surface firing. This is accomplished in either of two ways, depending on whether or not Ordalt 2331A has been accomplished. If Ordalt 2331A has not been accomplished, the system time constant is increased by resorting to manual rate control. The procedure for this type of operation is given later in this chapter.

If Ordalt 2331A has been accomplished, the time constant is increased by setting the AIR-SURFACE selector (figure 28) at SURFACE. This makes the solution time constant KR/R'X 1000 seconds, where K represents the time constant change gears in seconds, R is the present range in yards, and R' is the setting of the time constant control transmitter. Since this value becomes rather large at long range (fig. 41), provisions are made to reduce the time constant if necessary. When the sensitivity push button (fig. 28) is pressed, the time constant is reduced to approximately 72/4000 seconds. If the time constant stayed at this value, the system would be too sensitive for surface fire; therefore, after a given delay (2 or 3 seconds), the time constant automatically returns to its previous value which is suitable for tracking and spotting most surface targets.

Manual Rate Control
In certain instances, manual rate control is desirable when a surface target is being engaged. Probably the most desirable advantage is that it permits the computer operator to increase the system time constant; thereby giving a stable solution which results in the low dispersion that, for spotting purposes, is desirable in surface firing.

     AT THE COMPUTER (fig. 42) :
        a. Set the target angle handcrank selection

Direct Fire
Whenever possible, direct fire should be used against shore targets. When this is done, the procedure for operating the Gun Fire Control System Mk 37 is essentially the same as for firing against surface targets, except that it is usually necessary to use optical tracking in train, elevation, and range. Unfortunately, due to conditions that accompany a shore bombardment, direct tracking is not always possible; hence indirect fire or offset fire must be employed.

Indirect Fire
In instances where the target is obscured, the Gun Fire Control System Mk 37 may be used to direct destructive fire as shown in figure 45. In this method the point that is tracked by the computer is always the desired point of fall. A chart, which includes the ship and target positions, is used to determine the target position with respect to the ship. As this method requires an accurate plot of the firing ship's position on a chart that includes the target area, and the gun director is not required for other operations, the gun director can be used to determine the ship's position with respect to the shore by taking ranges and bearings to known points. The following paragraphs outline the operations required to shift the Gun Fire Control System Mk 37 from the stand-by condition to the setup for indirect fire.

Tracking.
At the computer (fig. 36) set the control switch at LOCAL, and the target speed hand crank selector at HAND. By means of the target speed hand crank, set the target speed counter at zero. (NOTE: Since the pitometer log merely indicates the speed of the firing ship through the water, some activities have found it desirable to set the computer target speed counter at the speed of the current at the ship's location and to set target course at the course of the current plus 180 degrees. This counteracts the effect of the motion of the water and allows the computer to generate correctly.) Set the synchronize elevation handcrank at the CENTER position. Set the elevation dial at zero. Then set the synchronize elevation handcrank at the OUT position and match the dip dials with the advance range counter. Turn the generated bearing and generated range cranks until the true bearing and generated range dials agree with the values indicated by the chart. If firing at an elevated target, make the appropriate setting on the elevation spot dial. Set the time motor switch at ON.

Firing.
Commence firing. Spots received from the shore fire control party or aircraft should be applied by means of the range and deflection spot knobs (fig. 11).

Offset Fire
Offset fire, which is indirect fire with a point of aim, may be employed to advantage by the Gun Fire Control System Mk 37 when engaging targets with a known relationship to a good optical or radar point of aim. Although offset fire in most instances is not considered as effective as full indirect fire for engaging obscured land targets, it has to its credit the advantage of a reference point for checking the computer solution and the fact that in emergencies, offset firing may be conducted without the use of previously prepared charts of the area to be bombarded. In general, offset firing with the Gun Fire Control System Mk 37 can be done in two ways.

Method 1.
The operation of Gun Fire Control System Mk 37 during offset fire—Method 1 (called the "Point Oboe Method" by several fleet activities) is indicated in figure 46. Here the gun director tracks the offset reference point and the computer solves the problem using the point of aim as a target.
The point of impact of the projectiles is

Figure 49. Type B Radar Presentations of the Problem in Figure 48.