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1. The General Electric Company developed this fire control installation. It was installed in the Maryland and Colorado in about 1922. Later, in a modified form, it was installed in the West Virginia. It uses the "Selsyn" transmission system.


2. See Plate No. 1, Schematic Main Battery Elevation Sys tem. The numbers in the text below refer to this plate.

3. Any director of the system can control in elevation. Di rectors are in the following stations:

4. One director is designated controlling director. The pointer has a director correction handwheel (1) by which he adjusts his sight (2) to the suitable Director Correction (D.C.) for the roll. A mechanism (3) on which the parallax range is set by handle (4) automatically corrects the Director Correction for Vertical Parallax (V.P.). The resultant of director correction and vertical parallax is transmitted by generator (5) electrically to the director correction bus for distribution. From this bus the D.C. goes to a zero reader (6) on one of the auxiliary gun directors in plot.

5. This zero reader is kept matched by setting the director correction manually by handle (7). In addition to matching the zero reader, the movement of handle (7) also indicates director correction on the Director Correction Dial (10) end also introduces director correction into differential (9). Advance range is received electrically from the rangekeeper and is indicated on the Range Indicator (23). By moving handle (8) range dial (11) is made to agree with the indicated range. The range, converted into minutes by the mechanism, is introduced into the differential (9). The differential (9) combines the advanced range and the director correction. The output is Gun Elevation Order (G.E.O.). This goes to generator (12) which transmits G.E.O. electrically to transformers (13) on the Elevation Indicators at all pointers' stations in all turrets.


Plate 1


6. Transformer (13), called a "repeat back element", is a, combined electrical and mechanical differential. Here the "ex isting gun elevation" (Note: Tnen the,guns are properly laid Existing Gun Elevation Equals Gun Elevation Order plus Roller Path Compensation Erosion) corrected for the compensation for erosion and roller path compensation is deducted from the Gun Elevation Order electrically received and the resultant is indicated on a zero reader (14). The zero reader indicates the amount and direction the gun must be elevated or depressed to make "existing gun elevation" agree with G.E.O. received.

7. As stated above (assuming the gun is properly laid), "existing gun elevation" is the algebraic sum of the Gun Elevation Order, roller path compensation and erosion. Elevation rack (15) transmits gun elevation to differential (16). The roller path tilt compensator (17), actuated from the turret train rack (18), introduces the roller path compensation for the angle of train into differential (16). This differential removes the roller path compensation from the gun elevation leaving G.E.O. plus Erosion. This component goes to differentials (20) and (22). At differential (20) director correction is introduced by handle (19) and the differential removes B.C. from G.E.O. leaving actual sight depression which goes to the erosion corrector (25). Rounds fired are set by handle (21). These two introduced values in the erosion corrector determine the erosion correction which goes to differential (22) where the erosion is removed from G.E.O. plus Erosion. G.E.O. alone remains. This goes to angle reading dial (24) and to the transformer (13).

If the gun is elevated to the proper elevation the G.E.O. thus received mechanically is the same as the G.E.O. received electrically from the auxiliary gun director. In that case, the zero reader (14) will be matched.


8. See Plate No. 2, Schematic Main Battery Train System. The Numbers in the text beloxv refer to this plate.

9. There are five controls for director fire train:

Rangekeepers are used in case the target is obscured from the director (indirect fire).

10. The trainer of the controlling director trains his telescope on the target. The training wheel and gearing drive a


generator (1) which transmits relative target bearing to the director train bus.

11. Directors in the foretop and maintop have horizontal parallax mechanisms attached. Since director in the foretop is so close to the reference point in train, i.e., the firecontrol tower, its horizontal parallax mechanism is locked on zero. The mechanism functions on the maintop director. It introduces an angular displacement between the telescope and the training element, this angle being equivalent to the parallax angle to the fire control tower for any definite range and bearing of the target. Thus the director in the maintop, when trained on the target, transmits the bearing the telescope would have if it were located at the point of reference. The horizontal parallax mechanism is not shown in the schematic diagram.

12. The target bearing from the director train bus goes to various ship bearing indicators (2), to the auxiliary gun director transformer (4) and to the rangekeeper (3). Both of the latter instruments are in the plotting room.

13. The rangekeeper generates the deflection which is transmitted electrically to the deflection indicator (5) on the auxiliary gun director. The operator keeps this deflection set by means of handwheel (6). The deflection set is registered on dial (7). By setting deflection by handwheel (6) the deflection is introduced mechanically into transformer (4) which also re ceives electrically the relative target bearing, as stated above. The transformer (4) adds together algebraically the deflection and relative target bearing as received to produce "corrected target bearing" or Gun Train Order which is transmitted to the Turret Train Transmitters Mark III at the turret racks.

14. Also in plot is a Parallax Range Transmitter located near the rangekeeper. The operator of the Parallax Range Transmitter reads the range from the rangekeeper and sets it by andle (8). This set range is indicated on dial (9) and is also entered into the generator (10) of the Parallax Range Transmitter. This generator transmits the parallax range to the parallax range receiver element motor (11) in the Turret Train Transmitters Mark III. This motor actuates a servo motor (12) which can also be actuated by hand crank (15). This servo motor ad justs the parallax mechanism (14). The parallax mechanism consists of a system of cranks and levers which rotates the staters of the train repeat back transformer (16) and of the train transmitter generator (17) by the amount of the parallax angle between the turret and the reference point.

15. As stated above, Gun Train Order comes from the auxiliary gun director to the train repeat back transformer (16). Actual train of the turret is introduced mechanically by means of pinion


Plate 2


(15) to the repeat back element (16). The "repeat back" element deducts the actual train of the turret (as modified by the parallax correction) from the gun train order and indicates the difference on the zero reader (18) of the train indicator at the turret trainer's station. When the zero readers are matched the turret is trained on the proper bearing.

16. The actual train of the turret (15) is also introduced into the train transmitter generator (17). This generator generates actual train of the turret compensated for the parallax (which is applied by mechanically offsetting the stator) and transmits this value (which equals gun train order if the turret is matched) to the multiple turret indicators in plot and the fire control tower.

17. Actual turret train is also transmitted mechanically from pinion (20) on the train rack to the generator (21) of the turret train transmitter Hark II. This generator transmits actual train of the turret to motors (22) and (23) of the Double Turret Train Indicators in the Officers' Booths of own and adjacent turrets.

Divided Fire.

18. In elevation the following directors may control so as to transmit the "director correction"

19. In train, the following may control so as to transmit relative target bearing:


20. The auxiliary gun director #1 and parallax range transmitter #1 in plot are used with the forward group; auxiliary gun director #2 and parallax range transmitter #2 are used with the after group.

Indirect Fire.

21. In case aloft directors are disabled the director correction (B.C.) is supplied to the auxiliary director by the gun director Mark XIII located in the plotting room. The director consists essentially of (a) an element stabilized by the action of two opposed gyroscopes, carrying an artificial horizon against which D.C. may be observed; (b) a target bearing mechanism carrying a telescope arm and director correction mechanism which is constantly trained on the bearing of the target so that the telescope will observe the director correction angle on the proper bearing; (c) a telescope which may be given any director correction angle so that when telescope crosslines pass the artificial horizon due to the ship's roll, the observer can fire; (d) Selsyn generators to transmit the director correction to the auxiliary gun director.

22. For relative target bearing in case of indirect fire one of the rangekeepers and its target bearing relay transmitter Mark V Mod. 1 is put in control. The rangekeeper generates the compass bearing of the target and sends it to the target bearing relay transmitter which also receives "compass" electrically. The target bearing relay transmitter subtracts "compass" from the generated compass bearing of the target and electrically transmits the resultant, namely generated relative target bearing, to the director train bus.

Special Motes.


23. In the Maryland - Colorado the switching arrangements are such that if director 1, 2 or 3 (Foretop, maintop end fire control tower) is used at all it must control both in train and elevation (A rangekeeper may control in train while a director controls in elevation). Later installations have more flexible switching arrangements.

Multiple Turret Train Indicators (in Plotting Room and Fire Control Tower).

24. On the Maryland - Colorado there are a pair of dials for each turret, one coarse and the other fine. The coarse dial has a turret painted on it and indicates the approximate train of the turret. The fine dial has a pointer indicating accurately


the turret train corrected for parallax. In later installations the FINE DIALS are zero readers and show the turret' s error in matching; with the received Gun Train Order.

25. The West Virginia installation is similar to the Maryland - Colorado installation as 'described above. Instruments in the West Virginia installation carry out the same functions as in Maryland. However the instruments have some refinements. over the Maryland type and the system is more flexible on the West Virginia due to the better switching provisions.


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Transcribed and formatted by Thomas Wildenberg