THE MECHANISM OF FIRE CONTROL The installation used for fire control was intricate in the years before 1914, and war experience has made necessary the addition of further complications. The perfecting of the fire control or ganization of any ship is the most important item in making hei into an efficient fighting unit, and it requires painstaking exercise lasting over many weeks. Little can be said of the details of the various instruments used. Each navy regards its installation as confidential, and the functions, and even the existence of some instruments, are kept as secret as possible. The main problems are, however, the same for all and may be divided into three parts: (I) the communications between the control stations and the guns ; (2) the apparatus for obtaining the hitting range and deflection and for keeping them both correct; (3) the arrange ments for firing the guns and for observing the fall of shot.
Communication must be maintained be tween the observing stations aloft, the principal control position, the transmitting station and the gun positions. As most of the information is only of value at the moment of transmission and loses its significance if delay occurs, communications must be rapid and sure, and hence several lines usually exist between im portant stations. All lines of communication are generally concen trated into the transmitting station, which is situated well below the armoured deck in the quietest place that can be selected. Voice-pipes are used between stations that are moderately close together. A voice-pipe must be as straight as possible and there are well defined limits of length for each diameter of pipe, beyond which the acoustic properties are lost. The telephone is used between all stations and there is usually a telephone exchange, in or near the transmitting station, solely for the use of the fire control organization. The telephone transmitters and receivers are specially designed for use by operators who have other duties to perform, or for instruments that are exposed to the weather or the blast of the guns. Electro-mechanical transmitters and receivers are used for passing ranges, deflection, bearing, orders and other information of a standard character. There are many different patterns of these instruments, those most commonly used in all navies being the Barr and Stroud "step by step," the Vickers "counter" and the "follow the pointer" types.
In the transmitting station are situated the majority of the calculating instruments, and to this position are passed the results of all observations of range, etc. The functions of most of these instruments are confidential. Broadly, they consist of arrangements for deducing the course and speed of the enemy from the data available and for calculat ing from this the rate of change of range and the deflection to be applied to the gun sights. In the British service the Dreyer calcu lating table is in general use and to this, the details of which are secret, constant improvements are being made. In all navies some form of calculating apparatus is used, and there are a num ber of patented sets of instruments, notably the Argo and the Ford, which are designed for this purpose.
The Barr and Stroud coincidence rangefinder is the one most commonly used by all navies, and this instrument forms the equipment of the British fleet. In a capital ship there are at least six large rangefinders, and the number and size of the instruments are reduced proportionately in smaller ships. The observations of each instrument are transmitted electrically to the transmitting station, where apparatus exists for obtaining a mean of all the observations, thus giving what is called the "mean rangefinder range." To this are applied the corrections for the density of the air, the effect of wind, the change of range during the flight of the projectile and for several other variables. (See also RANGE-FINDERS.) Change of Range Calculators.—To obtain the rate at which the range is changing at any moment involves the solution of two triangles, the functions of which are the course and speed of the firing ship and the bearing, course and speed of the target ship. The first two of these are known, the third is easily observable, but the last two can only be obtained by calculation or be judged approximately by observation. The speed of the target must always be guessed in the first instance, and instruments known as inclinometers are used whereby the angle between the line of fire and the course of the target ship can be observed with fair accuracy. There are several types of change of range calculators: that used in the British service is the Dumaresque, in which the elements are set graphically and the resulting rate of change of range is read off in "yards per minute," which is what is required.
type of clock, which can be set to run at the rate at which the range is changing, is used by all navies. In the British service the Vickers clock is used. This consists of a powerful clockwork escapement, driving a large pointer round a clock face, the perimeter of which is graduated in yards. A method of altering the speed of the pointer is fitted, so that it can be made to run at speeds of o to 2,000 yards per minute in either direction (i.e., increasing or decreasing range) . Arrange ments are made for large corrections in range to be made to the perimeter of the clock without interfering with the motion of the pointer, so that the clock can always be run at the range that it is desired to transmit to the guns.
To obtain the correct deflection for hitting at long range is a difficult matter. There are many types of deflection calculators which give an approximation to the de flection, but all these instruments have their limitations. Allow ance can be made for the wind at the firing ship, but at long range the wind effect at the target may be entirely different. Also, the direction and force of the wind in the upper air through which the projectile passes are unknown factors. The practice is to calculate the proper setting as near as is possible and then to correct it by observation of the fall of shot. Correct deflection is of the greatest importance whilst ranging, for at long ranges, unless the shot fall in line with the target it is impossible to tell whether they are short or over.
Azimuth plates are carried in the con trol positions with telescopes mounted upon them. The zero is fixed in the fore and aft line of the ship and the bearing of any object with reference to this can be readily observed. In the Evershed type, used in the British navy, the bearings are trans mitted electrically and the instruments afford a ready means of indicating the correct target to the guns, but this system, even where still fitted, is now secondary to the Director (see below).
