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1. This system uses the Arma-type self-synchronous alternating current transmission system. The main battery gun control system is constituted of:

Gun Directors one forward and one aft. Either may control any or all of the four eight-inch turrets, exposed rangefinder or T.B.I, in conn.
Target-Bearing System Controlling director observes and transmits target bearing to T.B.I, in conn, director train indicators at each director, and range-finder train indicator in exposed range finder.
Turret-Train System Controlling director generates and transmits "gun train" at 1 and 36 speed to train indicators in each turret. Mechanically driven turret-train transmitters in each turret transmit "turret train" to double turret indicators in own and adjacent turret and to multiple turret indicators in fire-control stations.
Elevation System Controlling director generates and transmits "gun elevation" to an elevation indicator in each turret. Corrections for roller path tilt and erosion are introduced in the indicator.
Battle Order System Transmitter on controlling director transmits range, deflection and battle order to indicators at both fire control stations and at turret officer's station and sight setters station in each turret.
Fire-Control Switchboard Permits switching control, etc.
Motor-Generator Control Switchboard Controls either of two motor generators and auxiliary power source.

The Gun Director (Plates 15, 16 and 22)

2. Location. The gun director Mark XVIII is located in the forward main battery control station and the Mark XVIII Mod. 1 director, in the after control station. The Mod. 1 instrument has a parallax compensator to correct train outputs for parallax between the forward and after gun director stations and the


Plate 1


Plate 2


range drum graduations and range keeper range converter cam are different owing to the difference in height of the gun-director stations.

3. Function. The gun director is a combined observing, computing, and transmitting instrument for controlling the main battery guns. It is sighted on the target and cross leveled on the horizon. In conjunction with the range keeper, which is mounted on it, it supplies electrically pun elevation, gun train, and target bearing. Sight deflection and advance range are read on the range keeper face plate and set manually on the battle-order transmitter, Mark XII, which is also mounted on the director. Gun elevation includes correction for vertical parallax, cross leveling, roll (i.e., director correction), and ballistics applied as spots. Gun train includes corrections for cross-leveling, deflection, and ballistics. In the case of the after gun director, the gun train includes parallax correction. Target bearing is the bearing of the line of sight. In the case of the after gun director it includes parallax correction.

4. For any given range the gun elevation depends on the point on the roll at which the guns must be fired. The gun elevation is adjusted at the gun director for some point on the roll at which firing is desired, and the gun director automatic ally closes its firing contacts at that point. The pointer's and trainer's telescopes are of the periscopic type and look in to mirrors which are rocked by the gyro as the ship rolls. The lines of sight are thus stabilized so that the horizontal cross wires remain on the target. In order that the pointer may know when the guns are about to be fired, a small auxiliary firing scale is shown in his telescopic field. This scale moves up and down as the ship rolls and is shifted by the pointer's handwheel for the amount of director correction desired. When the horizontal line of this image, marked by an "X", coincides with the horizontal wire of the pointer's telescope, the automatic firing contacts will be closed. In case the firing relay is out of action, the pointer fires by pressing his firing key at this point. Thus the pointer will be able to control the guns intelligently. If the gyro is out of action, provision is made for locking it in its central position. The pointer's and trainer's sights can then be used, but they will not be stabilized. In this case the pointer will fire by pressing his firing key when the target rolls on the horizontal cross wire of his telescope.

5. Training Mechanism. (See Plate 15). The trainer's handwheels operate the train drive shaft, a sluing mechanism being provided, so that either training or sluing may be used. One revolution of the hand, wheels equals 8° train of the director when sluing, 2° train when training, the speed being reduced through a gear train on the train counter shaft, which is also


geared to the gun train dials, indicating gun train transmitted by the director. In the after director the gun train dials are driven through a differential, the other input being parallax correction from the parallax mechanism. Limit stops are provided on the train drive shaft, confining the director train to 3ftO°. The train drive shaft trains the director about the pedestal through a gear and pinion meshing in the stationary training rack on the pedestal. The gun train transmitters are driven by the train drive shaft, on the after director parallax correction being added through a differential. The target bearing transmitter is driven through a differential, one input being gun train from the train drive shaft (corrected for parallax on the Mod. 1), the other input deflection. The target bearing drive shaft also supplies the target bearing input to the range keeper.

6. The dummy gun bail trunnions are journaled in the trans- mitter belt casing, so that the bail is trained with the direc- tor, carrying the dummy gun muzzle and zenith ring with it. The deflection motor receives deflection electrically from the range keeper and supplies deflection mechanically to the deflec- tion worm meshing in the deflection sector. The deflection angle is thus applied to the deflection arm, since the sector is held by the zenith ring. The deflection arm thus trains the the correction bail and correction frame. The correction frame moves the pointer's and trainer's mirrors by the amount of the deflection and the director trainer moves his handwheels to bring his line of sight on the target, thereby correcting the gun train for deflection. A rack on the correction frame drives a pinion mounted on the main casing; this pinion therefore has deflection put into it which it supplies to the differential correcting gun train, obtaining target bearing as the input to the T.B.T. and range keeper, previously mentioned.

7. Gun Elevation Mechanism (See Plate 15). The function of the gun-elevation mechanism in the gun director is to automatic ally close the firing contacts at the correct point in the roll and to transmit to the guns the angle above the deck at which they should be elevated, proper allowance being made for the roll and pitch of the ship at the firing instant. The pointer's handwheels are used for adjusting the firing mechanism so that the guns will roll on the target. In other words, they are used to introduce director correction. They automatically add the di- rector correction to the sight depression which has been re ceived from the range keeper, the result being gun elevation. One revolution of the pointer's handwheels represents 1°.

8. The sight depression servo motor electrically controlled by the range keeper supplies minutes elevation corresponding to advance range corrected for vertical parallax. The S.D. motor drives a worm which positions the S.D. sector with respect to


the dummy gun, which corresponds to setting the sights. The S.D. motor also supplies sight depression as one input to the gun elevation differential. The pointer's handwheels supply director correction as the other input. The output gun elevation is transmitted by the G. E. shaft to the G. E. transmitters and to a worm meshing in the gun elevation sector and positioning the dummy gun bail. The S.D. sector and G.E. sector jointly position the zenith ring about the elevation axis; the vertical ring through the deflection arm controls the elevation of the correction bail. The latter through the director correction rod and trigger plate arm swings the trigger plate about the outer gim-bal trunnion, adjusting the position of the contact plate so that the contact rollers make contact to fire the guns at the proper instant for the existing D.C. A contact adjustment, is provided as a means of advancing the time at which the contacts are closed to allow for any lag in the firing circuit. The D.C. rod through two links positions the firing scale in the pointer's telescope field.

9. Stabilization of Pointer's and Trainer's Mirrors. The pointer's and trainer's mirrors which reflect the image of the target from the line of sight into the optical system are semi-stabilized by the gyro - that is, they are connected to the gyro so that as the ship rolls they rock only one-half as much. This keeps the target always within .the fields of vision of the telescopes. The reducing motion mechanism consists of a short stabilizing arm secured to and pivoting about the outer gimbal trunnion. The short arm is connected at the end to the long stabilizing arm which is attached to the rocker shaft. The long arm is exactly twice the length of the short one so that the rocker shaft, which rotates the mirrors, turns through half the angle through which the outer gimbal trunnion turns.

10. Stabilization of Gyro Gimbals. (See Plate 16). To stabilize the gimbal system there is a connection between the gyro and the inner gimbal. This connection is made by the bell crank (6) rotatably mounted on the gyro trunnion. The lower end of the crank is held against the gyro pin by a spring (8). The other end of the crank is held against the lever (5) by the spring (7). The lever (5) is mounted on a rod which is journal-ed by bearings in the lug (4), which is part of the inner gimbal. The rod can be rotated by a mechanical connection with an adjustment knob on the outside of the case, but except when adjustments are being made the rod and arm (5) remain fixed relative to the inner gimbal, so that they may be considered a part thereof. Since the gyro tends to remain fixed in space, as the ship rolls the gyro will rock relative to the gun director and the correction frame which supports it. If the gyro rocks clockwise about the stabilization axis, the gyro pin will press against the lower end of the ball crank (6). The upper arm of the bell rotate upward pulling the inner gimbal with it by


means of the spring (7). If the gyro rocks counterclockwise, the spring (8) will pull the bell crank (6) causing it to rotate counterclockwise. The upper arm of the bell crank will thus move downward and, pressing, against the arm (5), it will carry the inner gimbal downward with it. Thus there is a spring connection between the gyro and the inner gimbal so that any rotation of the gyro about the stabilization axis will result in a parallel rotation of the inner gimbal. The springs act as a cushioning and safety link between the gyro and gimbal, and they are necessary for operation with the gyro locked.

11. By means of the inner gimbal trunnions, the movement of the inner gimbal about the stabilization axis is transferred to the outer gimbal. This gimbal., which is thus stabilized, actuates the mirror stabilizing mechanism previously described and the trigger of the firing mechanism. Rotation of the gyro about the cross-leveling axis is unrestricted. The motion is transferred by the gyro trunnions to the inner gimbal which is free to rotate about its own trunnions.

18. Gyro-control handles. There are four gyro-control handles (See Plate 16):

  1. Cross-leveler's horizon adjustment.
  2. Coarse wander adjustment
  3. Fine wander adjustment
  4. Gyro-locking knob.

13. Cross Leveler's horizon adjustment. The cross leveler's horizon adjustment handle is connected to one of the trunnions of the outer gimbal by a system of levers, etc., including a spring coupling and trunnion clutch. The clutch allows the gimbal to rotate freely when no adjustment is being made. But when the knob is turned the outer member of the clutch overtakes the member which is fixed on the gimbal trunnion, thus making it possible to apply a force tending to rotate the trunnion and tilt outer gimbal about the stabilization axis. Through the inner gimbal trunnions the force is transmitted to the inner gimbal, As explained under the stabilization of the gyro gimbals, the inner gimbal is connected to the gyro by means of the parts (5), (6), (7), (8), and the gyro pin. Thus a force is exerted on the gyro tending to rotate it about the stabilizatioh axis. In this direction the gyro yields only slightly, but the applied force causes it to precess or rotate about the cross-leveling axis, which is at right angles to the stabilization axis. As the gyro moves about the cross-leveling axis it carries the inner gimbal with it, thus causing the desired movement of the artificial horizon line which is on the inner gimbal at the end of the gyro trunnion. The turning of the cross leveler's horizon adjustment handle thus causes the movement of the gyro about the cross-leveling axis, and this results in the raising or lowering


of the artificial horizon line in the cross leveler's telescope. When this line is on the horizontal cross wire and the latter is on the horizon, the gyro spinning axis will be in the vertical plane of the line of sight. The purpose of the spring coupling between the horizon adjustment handle and the trunnion clutch is to limit the pressure which can be applied by turning the horizon adjustment handle. The spring coupling is adjusted so that the applied pressure will be great enough to precess the gyro, but never, strong enough to overcome spring (7) or (8), and thus allow the inner and outer gimbals to be moved about the stabilization axis and relative to the gyro. Such a movement of the outer gimbal must be avoided because it would throw off the pointer's and trainer's mirrors in elevation, and if approaching the firing position it might swing, the trigger plate far enough to close the firing contacts. As an added precaution against this action, a caution plate near the horizon adjustment handle instructs the operator never to operate the handle when about to fire.

14. Coarse wander adjustment. The coarse wander adjustment knob controls the movement of the precession levers "A" and "B", the free ends of which will travel along the line "xy". (See p1. 16). When either of these levers contact with the tip of the gyro case, it exerts a force tending to rotate the gyro about the cross-leveling axis. The gyro, however, yields at right angles to the applied force and moves about the stabiliza- tion axis, carrying the inner and outer gimbals with it. The pointer's and trainer's mirrors, being stabilized by the outer gimbal, are also moved. By this adjustment the gyro spinning axis can be brought vertical in the vertical plane of the. line of sight. This brings the horizon on the cross wires of the pointer's and trainer's telescopes. The combination of the cross leveler's horizon adjustment and the coarse wander adjust- ment brings the gyro spinning axis to a vertical position. The target is brought on the horizontal cross wires by the fine wander adjustment knob.

15. Fine wander adjustment. The fine wander adjustment handle is used to bring the target on the horizontal crosswiros of the pointer's and trainer's telescopes by shifting the mir rors slightly with respect to the gyro. The handle moves a lever which .contacts with one end of a horizontal bell crank at a point in the line of the stabilization axis. The bell crank is pivoted on the outer gimbal, and the left end (in the diagram) contacts with a rod (1) passing through the trunnion of the in ner gimbal. This rod acting through the arm (2) and rod (3) causes the rotation of the arm (5). This arm contacts.with the bell crank (6) , which is held firmly against the gyro pin by the spring (8). The gyro by its inherent properties fends to remain fixed, but the inner gimbal is free to rotate about the stabil- ization axis. Hence if the end of the arm (5) tends to rise,


due to rotation of rod (3), it will be restrained by the end of the bell crank, with the result that the inner gimbal itself will be depressed about the stabilization axis. Conversely, if the end of arm (5) tends to go down, the tension of spring (7) will move the inner gimbal up. The movement of the inner gimbal above described causes the outer gimbal to move, and thus move the stabilized mirrors of the pointer's and trainer's telescopes. In this way the target can be brought accurately oh the horizontal cross wires. It should be noted that this adjustment causes no movement of the gyro itself. A dial viewed through a window in the cover of the case indicates to the pointer the position of the fine wander adjustment.

16. Handle for locking the gyro wheel. The gyro-locking handle is geared to a toothed sector on an iris-locking mechan- ism which acts like an iris shutter of a camera. The rotation of the sector closes the arms of the iris until they contact with the gyro case, bringing it to the central position. An additional lock is provided for securing the outer gimbal to the trigger-plate arm for independent firing when the gyro is out of action. When the gyro is unlocked, the gimbal lock is held out of engagement by a system of levers connecting with an arm on the iris mechanism. The initial movement of the iris in coming to the locking position releases the gimbal-locking pawl, and a spring will snap it into a slot in the gimbal as soon as the gimbal is brought to the engaging position. If the gyro has stopped, the engaging position is readily obtained before completely locking the gyro by tilting the gimbal system with the horizon adjustment handle. On account of the action of the spring coupling previously described this method can not be used if the gyro is still spinning. In this latter case the gyro is first locked by turning the locking handle all the way. The locking pawl is then brought into engagement with the gimbal by setting zero director correction with the pointer's hand-wheels.

17. Cross Leveling. The purpose of cross leveling is to correct the aim of the gun for the amount which it is thrown off in train and elevation due to trunnion tilt caused by the movement of the ship in a plane perpendicular to the line of fire. As the cross leveler turns his handwheel to keep the horizon on the cross wire, the cross leveling bail (See plate 15) is rocked about its trunnion axis. The bail is connected to the zenith ring by an arm, which causes the ring to rock as the cross level- er follows the motion of the ship in the cross leveling plane.

As previously explained, the zenith ring is tilted about the elevation axis by the amount of director correction. Hence for any case in which the director correction equals the gun elevation the zenith ring will be tilted by the same amount as the dummy gun is elevated and the gun will remain perpendicular to the plane of the zenith ring and therefore in its rocking axis.


In this case also its aim will not be disturbed by cross leveling and no correction will be necessary. This is as it should be, since if the director correction equals gun elevation it means that the gun is fired in the horizontal position where its aim is not thrown off by cross roll.

18. However, if the gun elevation is not equal to director correction, the dummy gun will no longer lie in the rocking axis of the zenith ring, and its aim will be disturbed. The dotted lines on Plate 15 show the dummy gun in an elevated position while the director correction is zero and the plane of the zenith ring is vertical. Now the rotation of the zenith ring which results in tilting the dummy-gun trunnions will tend to move the muzzle of the dummy gun from "a" to some point "b" out of the vertical plane of the line of fire. The point "b" will also be lower than "a". Thus both the train and elevation of the gun must be corrected for the amounts which they are thrown off due to the pitching or cross roll. Although the muzzle of the dummy gun tends to move from "a" to "b", this motion is prevented by its being held by the dummy-gun bail which does not partake of the cross-leveling motion. The bail therefore reacts through the dummy gun and rotates the zenith ring about train axis by the amount which a real gun would be thrown off. This action is the same as taking hold of the end of the dummy gun and moving it in train from position "b" back to "a". It is obvious that this would turn the zenith about its train axis. This rotation of the zenith ring results in an equal rotation of the pointer's and trainer's mirrors, to which it is connected by means of the zenith arms, deflection arm, correction bail, correction frame, etc.

19. The operations above described having thrown the mirrors off in train, the trainer will operate his handwheel to bring the vertical wire back on the target. This results in sending a train angle to the guns to correct for cross leveling. The cross leveling really holds the gun train to a constant angle in space as the ship pitches at right angles to the line of fire. Similarly, the dummy-gun bail in elevation reacts through the dummy gun and sight-depression sector, thus turning the zenith ring about the elevation axis. This action is equivalent to taking hold of the end of the dummy gun and elevating it by the amount necessary in passing from "b" to "a". The motion of the zenith ring about the elevation axis acts through the deflection arm, correction bail, correction rod, and trigger-plate arm, thus turning the trigger plate so that the gun director must roll to a different angle before the firing contacts are short-circuited by contact rollers. In case of independent firing with the gyro locked and the outer gimbal engaged with the trigger-plate arm, the movement of the latter will shift the pointer's mirror so that the target will roll on the horizontal wire at a different point of the roll. Thus the cross-leveling correction in elevation is effected. The effect of deflection


(which was assumed to be zero in the foregoing discussion) is to shift the rocking axis of the zenith ring so that it is no longer perpendicular to the plane of the ring. In this case the rocking of the zenith ring will change the elevation of the correction bail, thus applying a correction to the point of the roll at which the guns will be fired. It will also shift the correction bail a slight amount in train, thus applying a small train correction.

20. Range keeper. The Mark III range keeper is mounted on the right side of the forward gun director. The Mark III, Mod. 1, which differs only in the shape of the range converter cam, is mounted on the after director. No graphic plotter is used. The range keeper, from inputs of own ship's course and speed, target's course and speed, initial range and target bearing, and ballistic and spotting corrections generates and supplies sight deflection and sight depression to the gun director through servo motors. The instrument indicates on its faceplate advance range and arbitrary deflection, which are used in setting the range and deflection transmitter. By a pair of zero-reader dials located at a window in the left side of the case the instrument indicates the difference between generated target bearing and the train of the director telescopes to enable the director operator to continue to train the gun director in case the target is obscured. Range ballistic and range spots are applied by the range crank so that they are applied to the present range counter as well as the advance range. Wind ballistics for both deflection and range should be based on true wind.


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Transcribed and formatted by Thomas Wildenberg