Part B: Typical System
20B1. Introduction
In this section, the system installed on the Baltimore and Oregon City classes of heavy cruisers will be described. This system does not vary in principle from other main-battery systems. The discussion will include brief descriptions of the stations and instruments comprising the system, illustrations, and explanations of the connections between them, and details of several ways in which the system is used to track a target and to position and fire the turret guns. It is concerned primarily with the functioning of the various pieces of equipment as parts of an integrated system, and the part which the officers and men of the ship play in operating this system.
20B2. General features of the system
The main battery Consists of nine 8”/55 caliber guns mounted in three triple gun turrets. Turrets 1 and 2 are forward and turret 3 aft. All turrets can be trained through 300° (150° on either side of the centerline). The guns can be elevated 41 degrees above and depressed 5° below the deck plane. Each gun is independently controlled in elevation.
The fire control system is designed to aim and fire the guns at moving surface targets within the range of about 30,000 yards (approximately 15 miles).
Preliminary information concerning targets is transferred to the fire control party through the target-designation system, which has associated equipments located at various points on the ship, such as search-radar consoles and lookout stations. This information is combined with other estimated or measured quantities, whereby the system computes sight angle and sight deflection. The system also measures level and cross-level, and from all these data computes gun orders.
20B3. Principal system components
The system of fire control used on these ships is known informally as the Gun Director Mark 34 system.
Gun directors. The two primary directors are located above the main-battery fire control stations. Their basic function is to determine the LOS to the target by pointing the telescope or the radar antenna toward it. Range is measured by the radar or the rangefinder in the director and, together with target bearing, serves to locate the target’s present position. Under certain conditions, such as divided fire or casualty operation, the directors may assume some of the functions of the stable vertical and rangekeeper by measuring level and crosslevel and computing gun orders, using data furnished by auxiliary computing equipment. Corrections are made at the director for both horizontal and vertical parallax, based on the distance to the ship’s reference point and the mean height of the gun trunnions, respectively.
Plotting room. The plotting room (Plot) contains a stable vertical, a rangekeeper, some units of the radar equipment, and a main-battery switchboard.
The auxiliary main-battery switchboard is located in the after gyro room. It is connected to the system in such a way that it can substitute for the main-battery switchboard in Plot if the latter becomes inoperative. By means of this switchboard any director can be connected to any turret or group of turrets without using main-battery plotting-room facilities.
Turrets. Within the turret are three elevation receiver-regulators and a train receiver-regulator. These instruments control the hydraulic gear by which the turret is trained and the guns elevated in accordance with gun orders. These orders may originate at the plotting-room rangekeeper, at either of the aloft directors, or locally at the pointer’s and trainer’s handwheels.
The turret also contains one turret-train indicator and transmitter, and three gun-elevation indicators. These are follow-the-pointer units by means of which gun orders from the plotting room or elsewhere may be received electrically to be matched by handwheel operation. The train transmitter sends turret train for information purposes only to turret train indicators in various stations.
Also provided is a sight setter’s indicator, by means of which the sight setter sets the sights and supplies certain correction quantities for train and elevation instruments. In order to be independent of the rest of the system for local fire control, if necessary, the turret is also equipped with pointer’s and trainer’s gun-sight telescopes, a rangefinder, and an auxiliary computer.
Synchro transmission. The synchro transmission system transmits data and orders between the elements of the system. The single lines each represent a group of conductors. Selector switches at each fire control station and at each turret are provided to connect the turrets with either the main-battery or auxiliary main-battery switchboards. At the switchboards provisions are made for interconnecting the directors and turrets.
The firing circuits permit the guns to be fired by firing keys at various stations-in the directors, the plotting room, or the turrets. These keys are used for electric firing by hand keys. In automatic key firing, the guns are fired when contacts in the stable vertical are closed at a selected value of level or crosslevel. Ready lights and salvo signals are provided at all stations. Time-of-flight signals are provided at the directors and fire control stations, and in the plotting room.
20B4. Capabilities of the system
The fire control system may be operated in several different ways. This flexibility permits fire to be maintained in the event of casualty to parts of the system, and provides for firing at two or more targets at the same time.
Types of fire control. The different types of fire control are distinguished by the source and transmission route of the gun orders. The types of control are primary, secondary, auxiliary, local, and antiaircraft. These types, except the last named, are shown in figure 20B1.
In primary fire control, the target is tracked by one of the directors; gun orders are computed by the rangekeeper in Plot and transmitted to the turrets via the main-battery switchboard.
In secondary fire control, the target is tracked and gun orders are computed by one of the directors, with data supplied from the rangekeeper in Plot or from auxiliary equipment. Gun orders pass to the turrets via the main-battery switchboard.
Auxiliary fire control is similar to secondary fire control, except that the auxiliary switchboard is substituted for the main-battery switchboard in Plot.
In local fire control each turret utilizes local instruments and sights to solve the problem and aim the guns, and operates as a self-contained unit.
For antiaircraft firing, provision is made to connect the main-battery system to receive gun orders from the secondary (dual-purpose) battery system, so that the 8-inch guns may be used for antiaircraft fire. The long range of these guns makes them useful for firing on enemy planes which are grouping for attack beyond the range of the 5-inch guns. Differences in ballistics between the secondary-battery and the main-battery guns make necessary the application of corrective spots to the gun orders computed in the secondary-battery computer. This limits the effectiveness of this system against aircraft.
Methods of gun laying. Figure 20B1 is a schematic diagram showing the available types of fire control and methods of gun laying and of turret drive.
The different methods of operation by which the guns may be positioned are: automatic gun laying, in which the receiver-regulator controls the A-end; indicator gun laying, where an indicator is used to guide the handwheel operator; or local gun laying, where the gunsight telescopes are so used.
Methods of drive. The methods by which the handwheels control the driving of an element are local power drive and hand drive. In local power drive the handwheels are geared to the receiver regulator, which in turn controls the A-end of the hydraulic gear. In hand drive the handwheels are geared to the A-end and thus control the hydraulic drive directly. Both of these methods of drive use an electric motor to supply power to the hydraulic gear for moving the element; the handwheels govern only the volume of fluid that is pumped by the A-end. In manual drive the electric motor is inoperative, so the A-end is driven by man-power applied to an emergency hand crank. The operator’s handwheels (pointer or trainer) function as in hand drive.
In primary fire control, secondary fire control, and auxiliary fire control, either automatic or indicator gun laying may be employed. In local fire control, local gun laying must be employed. In both indicator and local gun laying, either local power or hand drive may be used, but in automatic gun laying these methods are not applicable.
Means of firing. Gun firing may be either by local key or by master key or by percussion; but percussion is used only when electric firing fails. Remote master keys at various stations in the ship may be used. In primary fire control, selected level or selected cross-level automatic key firing may be done automatically by the firing mechanism in the stable vertical. This method is not available in other methods of fire control.
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