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CHAPTER 11.
CONSOLIDATED SYSTEM OF FIRE CONTROL MAIN BATTERY.
Light Cruisers No. 26 Northampton, 13 June 1930
" 27 Chester, do
" 28 Louisville, 13 March 1931
" 29 Chicago, do
" 30 Houston, 13 June 1930
" 31 Augusta, 13 March 1931
1. Transmission - Selsyn System for operation on 115 volts,
60 cycles, single phase. Secondary voltage is to be nominally
90 volts.
2. The battery consists of nine 8" - 55 caliber guns mounted
in 3 mounts. Full charge M.V. is 3000 f/s and for reduced
charge is 2300 f/s. A
special target practice velocity of 2700
f/s is also used.
3. For directing the battery there are available two gun di
rectors, one forward and one aft, and two Marie VI range keepers.
The range
keepers are located in the plotting room.
4. The battery may be used entire or may be divided into two;
the one including one or two forward triple mounts under control
of forward
director and No. 1 rangekeeper, the other consisting
of the remaining triple mount under the control of the after gun
director and the No. 1
rangekeeper. When the battery is used entire either director may direct the fire with the assistance of
either rangekeeper.
4. Four methods of fire are available:
(a) Primary Control. The normal method of fire, using one
of the gun directors aloft and one of the range keepers in the
plotting room.
(b) Secondary Control. One of the aloft directors is operated like a broadside director, range and deflection being set
on the director,
using either data from the plotting room range
keeper, or from a Mk. VII range keeper attached to the director.
There is no cross-level
compensation in this method.
(c) Auxiliary Control. Exactly like Secondary Control, except that all electrical connections go through an auxiliary
switchboard aft.
In case it should
become necessary to use this
method, it is unlikely that the plotting room range keeper would
be/available, and the
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rangekeeper on the director would be used.
(d) Indirect fire. Gyroscopic standards of elevation and
train are included in the Mark VI range keeper, which can control
the train and
elevation of the guns and fire them.
--99--
6. The point of
reference in train is the center of rotation of the gun director in the after main battery control station.
7. The plane of
reference for vertical parallax is the horizontal plane through the mean trunnion height of the 8" enclosed mounts.
8. The forward
director is provided with a parallax mechanism for both vertical and horizontal parallax.
9. Each gun director is provided with a pointer's and a
trainer's sight. A pointer's handwheel turns a pair of selsyn
generators to communicate
gun elevation to the guns and the
rangekeeper. A trainer's handwheel trains the director and
turns a pair of Selsyn generators to transmit the
target bearing to rangekeeper and elsewhere as necessary.
10. The pointer's sight is provided with.a movable prism or
mirror in its optical system whereby the elevation of the line
of sight may be
adjusted to and maintained in the proper relation to the elevation of the guns. This prism is under remote
control from the rangekeeper and
the pointer does not ordinarily control directly the elevation of his line of sight, though
means are provided whereby it may be set to known
sight depression in accordance with the range, by hand, in emergency conditions, ("secondary" and
"auxiliary" control).
11. The Mk. VI range keeper contains, in addition to the
rangekeeper proper:
A ballistic computer.
A graphic plotter.
A cross-level corrector.
A gyroscopic unit.
A gun director (for indirect fire), and
A rate control mechanism.
Transmitters and Receivers.
12. The range keeper is set by hand for:
Own ship's speed. Target's course and speed.
Wind direction and velocity. Present range.
Range and deflection spots.
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It receives automatically:
Own ship's course from the compass.
Gun elevation order from the controlling director.
Relative target bearing from controlling director.
--100--
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Ballistic data as to the motion of the projectile is incorporated in the ballistic
computer, which is set for one of three initial velocities. The
ballistic computer does not
compensate for errors due to variation in initial velocity.
13. The range keeper generates range and bearing and solves
the fire control problem. It computes D.C. and transmits to
the controlling
director the director correction which will
place the director pointer's line of sight at the correct angle
of elevation with respect to the guns for
the existing advance
range and cross roll error. It modifies the observed relative,
target bearing from the controlling director by adding
deflection and cross roll correction in train, transmitting the resultant gun train order to the guns.
14. The reason for the method of controlling the elevation
system used in the Consolidated System is that the trunnion tilt
(cross-roll)
compensation originates in the range keeper and,
since it varies continuously as the ship rolls and pitches, it
was thought preferable that the
range keeper should be permitted
to weave the line of sight up and down' through the small angle
involved rather than to weave the guns up
and down.
15. It was not considered feasible to avoid weaving the guns
back and forth in train, so the cross roll correction in train
was applied direct to
the gun train order.
16. The graphic plotter automatically draws curves of present range, advance range, true target bearing, and true gun train.
17. The gyroscopic unit contains a "level" gyro and an
"angle" gyro. The level gyro's axis is maintained vertical by
applying precessional
forces as necessary to level up a system
of bubbles mounted in a small auxiliary gimbal system located
at the upper left side of the range
keeper. In case of casual
ty to the level gyro, these bubbles are kept level and used as
standard. The level gyro furnishes the range keeper
with the
cross-level angle. It also
furnishes a level reference for firing the guns from the rangekeeper in indirect fire. The level
point may be
checked accurately against the horizon by "marks"
given by the director pointer.
18. The "angle" gyro is a standard of reference in train,
its axis pointing always horizontally in the direction of the
target. The bearing of the
gyro axis is the generated Relative
Bearing, and is transmitted through busses on the switchboard
to target designators on the directors. It
may also be used in
plane of observed relative bearing to obtain gun train order
(indirect fire). The angle gyro is free of the errors of a
north-
seeking gyro, and is therefore available for use during
--101--
indirect
fire at times when the gyro compasses would not be reliable. However, provision is made for using
the gyro compass as a standard
in case of trouble with the angle gyro. As an additional feature the angle
gyro, in conjunction with a bearing integrator, functions as a gyro
compass,
and may be compared with the ship's gyro compass by means of a dial.
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19. The
range keeper as a gun director. When the target is
obscured, or casualties occur, control may foe shifted to the
rangekeeper, and
indirect fire used. The-rangekeeper will transmit to the guns the generated relative target bearing (controlled by the "angle" gyro), plus
deflection and cross-roll correction. The director pointer
operates a crank which sets the gun
elevation order into the rangekeeper and
transmits it also to
the guns. The range keeper computes the director correction
just as it does when the top director is in control, but in this
case the director correction is visually compared with level
angle from the level gyro, by means of a "firing point dial",
which enables the
pointer to change the gun elevation order until the level angle and the director correction will be equal at some
part of the roll. The battery
may
be fired when these two angles are equal by an automatic firing device,
(provided a hand firing key is closed), or independently by the
director
pointer when the firing point is reached, as shown by the dial. In either case the level gyro is used as the standard.
20. The rate control mechanism provides a means for automatically correcting the target's course and speed so that the
components of the
target's motion along and across the fire as
resolved by the rangekeeper from the course and speed as set
will agree with the observed motion
along and across the line
of fire. If the generated bearing strays off from the observed,
it is only necessary to wait until it has moved off for a
period of one minutes, then to push in and turn a crank until the
generated bearing again equals the observed, which is indicated
by pointers.
The rate control mechanism will simultaneously
change the target's course and speed settings in such a way as
to correct the bearing rate
without changing the range rate.
Similarly, the range rate may be corrected by the rate control
mechanism, which will change the target's
course and speed set
tings so as to correct the range rate without varying the bearing rate.
Operation of the System.
21. The director trainer keeps his sight on the target by training the director and
incidentally transmits the target bearing to the range keeper
as basis for the
gun train order that finally issues therefrom. In the range keeper the corrections for cross leveling and deflection are applied.
--102--
22. The angle of train of the gun mounts, corrected far horizontal parallax, is transmitted mechanically to the gun train
indicators and
combined in an appropriate manner with the angle
of train transmitted from the range keeper, so that when the
zero reader dials in the gun
train indicators read zero, the
gun mount is trained to the desired angle of train; The angle
of train of the gun mounts, corrected for horizontal
parallax
to the point of reference, is transmitted electrically to appropriate dials in the mount train indicators.
23. The range function of horizontal parallax is transmitted
mechanically from the sight setter's station to the local gun
train indicator.
24. The director pointer observes whether his line of sight
is too high or too low and if he judges it to be so, turns his
handwheel to make the
appropriate change. The turning of the
handwheel does not move his sight directly but moves the gunerators that communicate gun elevation
order to the guns and
the range keeper. The guns respond directly to his signal by
elevating or depressing as required. The range keeper
responds
by transmitting to the pointer's sight and applying thereto, by
direct remote control, a new director correction corresponding
to the
new gun elevation and to the existing range and trunnion
tilt. Thus the elevation of the
guns is controlled by the director pointer himself arid
cannot be disturbed by changes in
range or by trunnion tilt compensation as the ship rolls and
pitches. Presumably the director pointer will
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not disturb the
elevation of the guns unless the accumulated change of range or list
makes it necessary in order that his sight may come on
the target
properly. In any case he will know
when they have been disturbed so as to refrain from firing at that instant.
25. For emergency use means are provided whereby the moving
prism or mirror in the pointer's sight, can be coupled through
suitable
gearing with his handwheel and the Selsyn generators
that transmit gun elevation. In this connecting gearing will
be provided a range
adjustment governed by a range drum whereby
a sight setter can set sight depression on the director. It
will thus be possible to use the
director in the same manner as
the "Tickers' Director is used if for any reason the range keeper is unable to exercise control over the pointer's
sight. Under the latter condition ranges will be taken from the Battle
order indicator or from the local rangekeeper arid set on the directors.
26. Gun elevation order indicators (1 speed) at the directors enable the director operator to match in elevation with the
controlling director, to
facilitate shifts in control.
--103--
27. The angle of elevation of the guns, corrected for inclination of the roller path and loss in muzzle velocity due
to erosion will be
mechanically transmitted to the gun elevation indicators.
28. The angle of train of the main battery directors or of
the anti-aircraft range finder mounts is transmitted electrical
ly to target designators
at the searchlight operating gear stations. Provision for modifying
this angle of train as desired
by the illumination control officer is made by
means of an arbitrary deflection device (electric differential) in the search
light battle order transmitters in the A.A. Control station.
These
battle order transmitters also transmit battle orders for
searchlight control to battle order indicators located near
searchlight operating gear
stations.
29. Provision is made on the switchboard to control the
train of all searchlights from either main battery director or
starboard lights from
starboard A.A. R.F. mount and port lights
from port A.A. R.F. mounts.
Instruments.
1 Gun Director Mark XXIV (foremast)
(To mount spotting glass Mark VII and Target Designator Mark V)
1 Gun Director Mark XXIV-1.
2 Range keepers, Mark VI
2 Target Designators, Mark V
2 Gun Battle Order Transmitters, Mark XVII
1 Target Designator Mark IT (2 exposed R.F. mount)
10 Battle Order Indicators Mark XVII (indicate range from 0 to 35950 yards)
3 Gun Train Indicators Mark XII-1
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3 Gun Elevation Indicators, Mark XI-I
5 Mount Train Indicator, Mark I, Mod. 2
(Mounts 1 and 2, plot and each MB control)
4 Mount Train Indicators, Mark II (Mount -fo, plot, and each M.3. control)
6 Bearing Indicators, Mark I-I
2 Battle Order Transmitters, Mark XVI (Stbd) (A.A. control stations) and Mark XVI-1 (port)
4 Target Designators, Mark IV-II (Searchlight gun operating stations).
2 Battle Order Indicators, Mark XVI (Stbd) and XVI-1 (port) Searchlight operating station.
7 Exciters, Mark III
1 Switchboard
2 Gun Elevation Transmitters, Mark I (Near each range keeper)
2 Tube Train Order Transmitter (O.S. 437) (On torpedo directors)
2 Torpedo Target Bearing Transmitters (O.S. 437)
2 Tube Train Indicators, Mark III (stbd) and Mark III-1 (port)
3 Motor generators for gyros.
2 Sets, Input and Output units for range keepers, consisting of Selsyn motors, transformers, etc.
3 20 volt Dynamoters.
To provide current for running the range keepers.
--104--
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