Chapter 26 Relative-Rate Anti-Aircraft Systems
Gun Fire Control System Mark 56, Page 3

A. Fire Control Problem
B. Basic elements of lead-computing sights
C. Gun sight Mark 15

D. Gun Fire Control System Mark 63
E. Gun Fire Control System Mark 56, Page 1
E. Gun Fire Control System Mark 56, Page 2
E. Gun Fire Control System Mark 56, Page 3
E. Gun Fire Control System Mark 56, Page 4
E. Gun Fire Control System Mark 56, Page

E. Gun Fire Control System Mark 56

26E10. Control officer’s station

The control officer has available the following operational controls:

1. Telephone-selector switch. This switch has three positions: AIR DEFENSE, LOCAL, and BOTH. The air defense circuit is used primarily for target designation; outlets are provided for the control officer, radar operator, target designation station, air defense station, and the other directors. The local circuit is used primarily for gun control; its outlets include the control officer, director operator, radar tracker, mount captain, and gun crew. When the switch is turned to BOTH, the two circuits are connected in parallel. But because of the number of outlets on these lines, the circuits are paralleled only for training and testing.

2. Slewing control unit, sighting unit, and slew switch. The control officer can slew the director in train and elevation at any time by pressing his slew switch. This will take control away from any other mode of tracking. The control officer slews the director by rotating the handgrips of the slewng control unit for elevation control and by rotating the head of this unit for train control. The target is followed by use of the binocular mounted on the sighting unit. The binocular is kept parallel to the line of sight by an elevation input to the crossarm. The left handgrip of the slewing control unit has a press-to-talk switch which is equivalent to the mouthpiece button of the sound-powered telephone.

3. Radar-optical switch. This switch selects the type of tracking when the slew switch is released. If the radar-optical switch is positioned on RADAR, the radar console controls the director power drives. When this switch is set on OPTICAL, the tracking control unit has control. Two small lights indicate the station in control. When the slew switch is closed, the control officer can still give control to one of the other stations by closing a precedence button on his handgrip. This causes a take-over buzzer to sound in either station, depending on the position of the radar-optical switch. The station at which the buzzer sounds can bypass the slew control by closing a take-over switch, a button on the handgrip of the tracking control unit, and the scan control foot switch at the console. This feature enables the control officer to relinquish control to another station while still slewing the director. To regain slewing control, he must release the slew switch, thus disengaging the precedence switch, and then close the slew switch again.

4. Cockpit data unit. This unit contains the telephone selector switch, target designation lamp, radar range dial, director train and elevation dials, and radar-optical switch.

5. Hand microphone. This is used by the control officer to give orders to the gun crews.

6. Cease-firing contact maker. This is for communicating CEASE FIRING order to the gun crew.

26E11. Director operator’s station

1. Telescope Mark 97. The director operator tracks a visible target by keeping the crosshairs of the telescope reticle on the target.

2. Tracking control unit. This unit is operative when the radar-optical switch is on OPTICAL and the slew switch is open; or when the slew switch is closed, precedence switch is closed, radar-optical switch is on OPTICAL, and director operator’s take-over switch is closed.

Since tracking signals are used in the computer as the rates of target motion, smooth tracking is of primary importance to the computation of accurate gun orders. To help the director operator track smoothly, the tracking signals from the tracking control unit are fed through an aided tracking circuit. For an instant after the tracking rates are changed, the director moves at higher rates than called for by the target’s motion. The result is that the line of sight hops closer to the target and then settles down to the new rates.

A firing key with a safety lock is inset in the right-hand grip of the tracking control unit. To close the firing key, the director operator must first release this safety lock by pressing the lever to the left.

3. The press-to-talk switch is located on the left handgrip of the tracking control unit. It is the equivalent of a mouthpiece button on the sound-powered phones.

4. The amplidyne power switch controls power to the amplidyne generators which supply the director drive motors. The amplidynes will not start before the gyro READY lamp lights, or the securing locks are off.

5. The cockpit illumination switch controls dial illumination to the cockpit dial unit and telescope reticle lamp.

26E12 Radar operator’s station


The radar operator has available the following operational controls (fig. 26E10):

1. Radar indicators. Two oscilloscopes, the A/ R-scope and the E-scope, provide the radar operator with his “view” of the target.


The A/R-scope,
figures 26E10 and 26El1, has a double-trace presentation. The lower trace (A-sweep) extends from 0 yards. The range mark is movable and can be set on the target pip. Scribe marks on the scope face indicate the graduations in yards. The upper trace (R-sweep) is the expansion of the A-sweep, 500 yards either side of the range mark. The range step remains fixed near the center of the R-sweep and coincides with the range mark. Echoes from stationary targets and the 1,000-yard markers (only one of which is visible at any time) move past the range step as the target pip is moved along the A-sweep.


The E-scope, figure 26E12, shows range (horizontally) in yards, and director true elevation (vertically) in degrees. The vertical width of the trace depends on the type of antenna scan. The range mark is a bright vertical line extending from top to bottom of the sweep. Target echoes are vertical lines in elevation. Two curved lines on the scope face furnish an indication of target altitude.

Although normal E-presentation is generally used, an expanded presentation is available by turning the elevation sweep switch to EXPANDED. Expanded sweep shows the same trace as normal, except that it is expanded in elevation and its center is fixed at the center of the scope. It gives no indication of director elevation.

2. The ranges slew lever is used for slewing the range mark to the target pip.

3. The range control switch is used to control the mode of range operation. When this switch is in its “normal” position, the range input signal may originate with:

a. Radar operator’s range slew lever.

b. Radar tracker’s range crank.

c. Automatic range-tracking circuit.

d. Range memory circuit (“coast” button).

c. Target designation station.

Other positions of this switch are Aided AA, Aided Surface, and Calibrate.

4. The radar-optical switch may be used by the radar operator to select the method of operation. This switch is connected in parallel with the control officer’s radar-optical switch, so that either station may select the method of control.

5. The elevation crank controls director elevation.

6. The scan control switch, which controls the type of antenna scan, is usually placed on the foot-switch position, so that the scan control pedal can be used to select the type of scan.

7. The coast push button allows the system to “coast” through radar interference such as: (a) obscuring echoes from objects close to the target; or (b) radar “blind spots” caused by own-ship structure. This push button cuts out the automatic tracking circuits and substitutes the memory circuits, which maintain the existing rates of motion in traverse, elevation, and range. The system will coast at these rates for as long as the button is pressed, up to a maximum time of about two minutes. However, the button should be pressed only long enough for the target pip to clear the interference. When the button is released, the automatic tracking circuits will lock back on target pip if the beam is sufficiently close to the target; if not, the console operators must get back on target manually.

8. The radar controls are the knobs on the de-modulater panel which control the operation of the radar equipment.

9. Range and elevation dials. The radar operator can read approximate director elevation and range from the normal E-scope presentation. For precise indications, he uses a fine and a coarse range dial, and an elevation dial which indicates elevation above the deck.

The range dials indicate the value of range being introduced into the computer (normally this is radar range). The designated range pointer indicates the value received from the target designation station.

10. The computer mode switch controls the mode of computer operation. On NORMAL, it allows the traverse and elevation tracking rates to be introduced into the computer as the rates of target motion.

On MANUAL INPUT, which is used for long-range surface fire (in which computer lead angles and ballistic corrections are not accurate), the computer does not calculate lead angles or ballistic corrections. Instead, it uses manually introduced values of sight angle and sight deflection as lead angles, combining them with director elevation and director train to produce gun orders.

11. The target-designation lamp located to the left of the tracking control lamps is lighted when the radar tracker has pressed his target designation push button and the system is synchronized with signals received from the target designation station.

12. The tracking control indicating lamps indicate the setting of the tracking relays. The three lights are labeled RADAR, SLEW switch, and OPTICAL.

13. The sight-angle and sight-deflection knobs and counters are used during long-range surface firing when the computer is operating in manual input. The sight-deflection counter is calibrated in mils; its zero setting is 500. The sight-angle counter is calibrated in minutes; its zero setting is 2,000. For normal operation of the system, both counters are set to their zero settings.

14. The take-over buzzer is located inside the console and indicates that the control officer wants the console operators to take over control for radar tracking. This buzzer sounds when both the slew and precedence switches are closed and the radar-optical switch is on RADAR.


Bottom of Page 3

A. Fire Control Problem
B. Basic elements of lead-computing sights
C. Gun sight Mark 15

D. Gun Fire Control System Mark 63
E. Gun Fire Control System Mark 56, Page 1
E. Gun Fire Control System Mark 56, Page 2
E. Gun Fire Control System Mark 56, Page 3
E. Gun Fire Control System Mark 56, Page 4
E. Gun Fire Control System Mark 56, Page 5