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1. The General Electric secondary battery type fire control installations are installed on certain battleships, light cruis- ers, and destroyers. These installations are very similar on all three types of ships.

2. The system has been installed on ships as follows:


the "Selsyn" transmission system. The type of installation described in this chapter was designed for controlling the fire of broadside batteries developing a high rate of fire. As in the Vickers broadside installation, there is no plotting room, the range and deflection being set on the director sights.

5. The Director (See schematic diagram, plate 1, and plate 12). The director is of the gun pilot type. In this type of director a member known as the gun pilot is elevated and trained as though It were on actual gun. The director is so constructed that the proper displacement of the telescopes from the gun pilot may be made to obtain a hit, both in elevation and train, regardless of the cross-roll, or "trunnion tilt". The elevation and train of the gun pilot with respect to the ship is transmitted to the guns and these quantities (plus or minus local corrections at the guns) are the proper amounts to elevate and train the gun - provided the director telescope is correctly pointed.


6. Sight Depression and Director Correction. (See Plate 2) Starting with the gun pilot and the telescopes parallel to the reference plane, assume that a range is set on the range dial*. This will not move the gun pilot but it will depress the pointer's telescope below the axis-of the gun pilot by an angle equal to the SIGHT DEPRESSION.

7. If the pointer using his handwheel now elevates his telescope to bring it parallel to -the -reference plane, the gun pilot will be elevated above the reference plane through the same angle. However the director pointer is free to elevate or depress his telescope above or below the reference plane through any angle (director correction) in selecting the firing point. The gun pilot is of course moved through the same angle.

8. In practice the director pointer is not concerned with either sight depression or director correction. He merely looks through his telescope and, with his handwheel, elevates and depresses as necessary to insure that his crosswires will cross the target. In doing this he unconsciously combines sight depression and director correction to obtain GUM ELEVATION ORDER, which is the angle between the gun pilot and the reference plane. Geared to the pointer's handwheel is a pair of transmitters (coarse and fine) which transmit the Gun Elevation Order to the guns.

* The range dial is graduated to include vertical parallax correction.


Plate 1


Plate 2


9. It should be emphasized at this point that the Gun Elevation Order transmitted to the guns simply causes, the guns to stay, parallel to the gun pilot, regardless of the range setting or the telescope elevation (director correction). If the range is correctly set on the director the guns will be properly elevated for firing when the director pointer's telescope is on the target. In other words the director is a master sight.

10. Trunnion Tilt (Cross Roll) Compensation in Elevation. As the ship cross-rolls the cross leveller cranks his telescope so as to keep it on the horizon at right angles td the line of sight. The operation of his handwheel rotates the pointer'stelescope about the gun pilot as an axis, thereby slightly elevating or depressing it(the pointer's telescope). This offset causes the pointer to fire a little earlier or later in the roll. The amount and direction of the offset is just enough to compensate for the trunnion tilt error in elevation.

11. Roller Path Compensator. There is no roller path compensator ±n the director. The inclination of the roller path itself may be adjusted in dry dock.

12. The Guns - Elevation. The Gun Elevation Order from the director goes to the rotors of the two transformers (coarse and fine) in the Gun Elevation Repeat Back.* The rotors of these transformers are geared mechanically to the auxiliary elevating rack on the gun, while the stators are positioned mechanically by the algebraic sum of erosion correction from the Erosion and Parallax Adjuster** and the roller path inclination compensation from the roller path compensator in the indicator. The electrical output of the stators is the difference between the Gun Elevation Order and the elevation of the gun (corrected for erosion and r.p. inclination. This output goes to the Elevation Indicator, which contains a pair of motors mounting dials which indicate to the gun pointer how to elevate. A pair of mechanically driven dials is included in the "Repeat Back". These show the elevation of the gun (corrected for erosion and r.p. inclination).


13. The Director-Deflection. (See Plates 1 and 3). If the director's deflection is set on arbitrary zero the gun pilot is trained on the same bearing as the director telescope (neglect ing trunnion tilt and horizontal parallax corrections). When a deflection is set, the director telescope is offset from the

* "Repeat Back" is a misnomer. It does not "repeat back".

** Which is kept set by the sight setter for rounds fired and range.


gun pilot. When the trainer trains back onto the target he offsets the gun pilot from the line of sight and thereby -applies deflection to the relative target bearing, yielding GUN TRAIN ORDER, which is transmitted to the guns. The guns therefore follow the gun pilot in train as well as in elevation.

14. T.T. Compensation in Train. The operation of the crossleveler's handwheel, acting through the gun pilot mechanism as explained in Paragraph 10, applies a further offset of the telescope from the gun pilot in train. This offset, as is the case with the T.T. correction in elevation, varies with the crosslevel angle and with the elevation of the gun pilot. If the director telescope is kept trained on the target the gun pilot will be continuously corrected in deflection for "trunnion tilt". So will the GUN TRAIN ORDER.

15. Horizontal Parallax - After Directors. The after directors each have an eccentric h.p. mechanism, so constructed that when the range is set the telescopes and gun pilot are offset properly to correct for h.p. from the forward director. When the trainer keeps "on" he automatically introduces the correction into the Gun Train Order.

16. The Guns - Train. The Gun Train Order is transmitted at 1 and 72 speeds to the rotors of two transformers in the Gun Train Repeat Back* at each gun. The rotors of these transformers are geared to the auxiliary training rack and the stators to the parallax mechanism, which is controlled by the gun train angle. and the range from the Erosion and Parallax Adjuster. Thus the relative position of the rotors with respect to the stators is gun train angle corrected for horizontal parallax between the gun and the forward director. The electrical output of these transformers is the difference between Gun Train Order and Gun Train Angle (corrected for parallax). This difference is shown by a pair of zero readers in the train indicator, thereby enabling the gun trainer to follow.

17. Divided Fire. As the guns on each side are divided into two groups with a group control station and director for each group, divided fire is easily: used. The switching equipment is such that any gun may be controlled by either director on the same side.

18. Indirect Fire. There is no provision for indirect fire.

19. Since the 5-inch guns can also be used for star shell duty two additional transmitting instruments are provided in each group control station. One of these, the Independent Train

* "Repeat Back" is a misnomer. There is no repeating back.


Plate 3


Transmitter Mark I (mounted near the director), can- transmit an independent train angle (i.e. independent of .the director) at 1 and 72 speeds, through suitable switches, to the five inch gun director train bus. The other, an Arbitrary Deflection Transmitter Mk I (mounted on the director) has a transformer which receives target bearing from a selsyn generator in the gun director at 1 (coarse) speed only, modifies it by an arbitrary amount of deflection and transmits the resultant to the director train bus.

20. The switching arrangement in the group control station is such that either the independent train transmitter can control any or all of the 5-inch guns when assigned to star shell duty.

21. The same generator which supplies target bearing to the arbitrary deflection transmitter can supply target bearing to the exposed range finders and to Director Train Indicators in either control station on the same side.

22. A separate generator in the director transmits target bearing at 1 speed to a transformer in the director the stator of which may be rotated by a hand crank to introduce any desired arbitrary deflection to the train of the searchlights.

23. Searchlights may also be controlled by the independent train transmitter but only at 1 speed. Searchlight Indicators have only a coarse dial.

24. Only the Independent Train Transmitter can be employed to transmit train angle to both the star shell guns and the search lights. In this case their control is independent of the director (useful for searching).

25. If it is desired to control the star shell gun and searchlights from the director which controls the guns which are firing at the target, the searchlight's must be controlled by the searchlight train transmitter, and, the star shell guns must (if they are to have separate deflection control from that of the other guns) be controlled by the arbitrary deflection transmitter at 1 speed only. Searchlights and star shell gun may be varied independently in deflection, but only the low speed dials are used.

26. Instruments are supplied to the various F.C. stations as follows:

  1. Group Control Stations:

      1 Gun director Mk XVI
      1 Arbitrary Deflection Transmitter Mk I 1
      Independent Train Transmitter Mk I 1
      Director Elevation Indicator Mk V 1
      Director Train Indicator Mk V


  1. Broadside 5" Guns:

      1 Gun-Train Indicator Mk V
      1 Gun Train Repeat Back Mk V
      1 Gun Elevation Indicator Mk V
      1 Gun Elevation Repeat Back Mk V
      Errosion and Parallax Adjuster Mk I

  2. Exposed Range Finders:

      1 Range Finder Train Indicator Mk V
      1 Range Finder Train Repeat Back Mk V
      1 Range Finder Train Repeat Back Mk V Mod. 1
      (For after exposed range finder only)

  3. Searchlight Control Stations:

      1 Searchlight Train Indicator Mk V
      1 Searchlight Train Repeat Back Mk V


27. The West Virginia secondary battery installation is a modification of the Maryland installation. Except for the important development indicated in paragraph 28, and the addition of a battle order visual system, the changes are of a minor nature. However they will be listed briefly:

28. Ball-bearing Mounted Zero-Reading Motors. In the Mary land, at each gun station there is a "repeat back" containing a "transformer" which electrically receives the gun elevation (or train) order, and mechanically receives the actual elevation (or train) of the gun. The difference is transmitted electrically to an adjacent selsyn "motor" which indicates to the pointer (or trainer) how to elevate (or train). In the West Virginia the repeat back and transformer are eliminated. Instead, the stator of the indicating motor is mounted in ball bearings and geared to the auxiliary elevation (train) rack. The position of the stator then represents the elevation (train) of the gun. This value is indicated on an "angle dial", showing the gun's angle of elevation (or train). The position of the motor's rotor with respect to the stator is determined by the gun elevation (train) order received. The directions of rotation of the stator and rotor are reversed, so that if, for example, the director is


trained to the right the zero pointer at the gun (attached to the rotor of the motor) will be moved by electricity to the left. Seeing this, the gun trainer instinctively trains right the same amount, thereby rotating the stator until it has mechanically carried the rotor back to the zero position. In the above explanation only one motor has been mentioned. Actually there are two: coarse and fine. Also the mechanical input to the stators is modified by corrections, such as horizontal parallax, erosion, etc. This elimination of the "repeat back" transformer is a big improvement, because it eliminates unnecessary units.


29. The light cruiser main battery (6-inch) installations are like the West Virginia Installation except as follows:


30. The destroyer installations are similar to the West Virginia installation, except as follows:

31. Unlike the light cruiser installation, there is no transmission of train to the AA guns.


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