A FIRE CONTROL SYSTEM FOR USE WITH MOBILE

SEACOAST ARTILLERY.

By Colonel Meade Wildrick, C. A.

Due to the types of heavy mobile artillery designed for our future Coast Defense System it becomes necessary to evolve a satisfactory fire control system to be used with these new weapons. Our present fire control system, due to its lack of mobility, cannot be used with guns that will have to take up positions where no fixed observing stations and telephone lines are installed, and which must be prepared for action. simultaneously with putting the guns in position. Therefore the new fire control system must meet the following requirements:

(a) It must be possible to install the system at any point along our seacoast in one or two hours time.

(b) It must be possible to send firing data to the guns by the time the guns are in position and ready for action.

(c) It must be capable of replacing our present fixed fire control system for our permanent armament when this fixed fire control system is put out of commission.

It is believed the fire control system here outlined will fulfill all the above requirements. Fortunately the topographical methods as developed in France and taught at the Coast Artillery School during the past year fit in nicely in this proposed system with our old fire control instruments, such as the Plotting Board (modified), Deflection Board, Pratt Range Correction Board, etc., and give us the solution to the problem as outlined above.

To illustrate the propsed system let us first briefly describe its component parts and then assume a hypothetical problem to show the manner in which it functions.

FIRING MAP

The basis of the whole system is an accurate map upon which is superimposed a quadrillage. This map is used for the purpose of locating base-end stations, gun positions,

datum points, etc., and for determining therefrom data with which to orient azimuth instruments, plotting boards, azimuth circles and sights. In other words a map similar to the French "Planchette de Tir," with which we are all familiar. Steps should be taken at once to prepare such a map to cover all our coastal and strategic areas. This map should be prepared by the Corps of Engineers, who have the facilities and necessary equipment for its proper execution.

THE PLOTTING BOARD

The plotting board to be used with this system is similar to our present board except that the base line arm is fixed and the graduations on the azimuth circles for both the primary and secondary arms are the same and are also fixed, running clockwise from 0° 180°. This has the great advantage over our old board of not having to orient the base line arm and of making the plotting board a universal board. See Fig. 1.

The gun arm azimuth circle is also fixed and is graduated from 0° 180°. There is an adjustable coupler which is scaled to correspond to the base line scale and which can be set to the length of the base line by means of a locking vernier. other words the proposed board is exactly similar to our present board with the above exceptions and due to its simplicity, it

In

would seem superior to other types of universal plotting boards. The rest of the fire control apparatus would be same as at present with the exception that the Tide Curve on the Pratt Range Correction Board would be replaced by an Elevation Curve, and would correct for the difference in level between the heights of the gun and actual water level (not mean low tide). A T.I. bell can be connected up on our Telephone Circuits.

OPERATION OF SYSTEM

To illustrate the manner in which the proposed system would operate let us assume the following hypothetical problem.

You are in command of a battery of Railroad Guns, or Tractor Guns transported on flat cars, and have been ordered from the Coast Defenses of Savannah to reenforce the mobile and permanent armament at Fort Monroe. Assume you arrive at Fort Monroe over the Chesapeake and Ohio Railroad at 7:00 A. M. Upon arrival you are ordered by your Group or Battalion Commander to put your battery in position at G immediately. See Fig. 2. You are told to locate your own base end stations.

You call your Orienteur Officer and tell him to locate the B' and B" stations as indicated in Fig. 2. You then notify your telephone details to lay the necessary lines from the base end stations, as located by the orienteur details, to the gun position at G, and to connect you up to the proper fire command.

The orienteur details then determine the co-ordinates of B', B" and G by the ordinary tepographical methods. To facilitate the location of base end stations, gun positions, etc., triangulative points such as P', P", Fig. 2, should be suitably marked and their position and co-ordinates printed directly on the map. The co-ordinates of some Datum Point such as Bug Light should also be printed directly on the map and can be obtained therefrom.

Let us assume the co-ordinates as determined by the orienteur details to be as follows:

We then have all the data necessary for computing the length and Y-Azimuth of the following lines:

Having computed the above data we can now orient the azimuth instruments at B' and B" and also the plotting board.

ORIENTING The Azimuth INSTRUMENTS AT
B' AND B"

As the graduations on the plotting Board run clockwise from 0° to 180° for both the primary and secondary arms we must orient the azimuth instruments at B' and B" to correspond with these graduatons. In other words the azimuth of the base line is always considered as 0° and the angles of intersection on any datum point or target are measured in a clockwise direction from the base line as a basis. Thus in Fig 2. the plotting board azimuth of Bug Light as measured from B' station is the angle a and is equal to the difference in Y-azimuth of the lines B' B" and B' - Bug Light. Similarly the plotting board azimuth of Bug Light from B" station is the angle ẞ or the difference in Y-azimuth of the lines B' B" and B" - Bug Light. Now set off the angle a on the azimuth instrument at B' and bring the instrument on Bug Light. Similarly set off the angle ẞ on the azimuth instrument at B" and bring this instrument on Bug Light. Both instruments are then oriented to measure angles in a clockwise direction from the base line B' B" and correspond to the graduations on the azimuth circle of the plotting board for the primary and secondary arms. See Figs. 1 and 2.

ORIENTING THE PLOTTING BOARD

Having computed the length and Y-azimuth of the line. B' G we can solve trigonometrically the right angle triangle B' G X, as we know the length of the hypotenuse B' G and the