The Germans evidently calculated with great care and experience upon the factors leading up to this famous long-range type of gun, which had an effective shooting distance of approximately 75 miles, which range, in the opinion of our experts, it is now quite easy for an experienced designer and manufacturer to equal and excel at will. In fact, one would hesitate to place a limit upon the length of range that could be achieved by a gun that it is now possible to design and build. In this connection it is interesting to note that the great French ordnance works at Le Creusot in 1892 produced the first known and well-authenticated long-range gun, which was constructed from the design of a 12-inch gun, but bored down to throw a 6-inch projectile. And instead of the usual 8 miles expected from the flight of a 6-inch shell this early Creusot long-range gun gave a range of approximately 21 miles with a 6-inch projectile, using a 12-inch gun's powder charge.
Closely connected with the development of the gun itself, and a necessary element of the gun's successful use, is the requirement that the weapon itself be easily transported from point to point, where its available range and capacity for throwing the projectile can be made of maximum use. This requires a gun carriage which has within itself various functions, the primary one being to establish the gun in the desired position where it can be made most effective against the enemy. Then, too, the gun carriage must have stability in order to withstand, absorb, and care for the enormous recoil energies let loose by the firing of the gun. It is obvious that the force which propels the projectile forward is equal to the reacting force to the rear, and in order to care for, absorb, and distribute to the earth this reacting force to the rear the carriage must have within itself some very peculiar and important properties. To this end there is provided what is known as a "brake" which permits the gun, upon the moment of firing, to slide backward bodily within the controlling apparatus mounted upon a fixed carriage.
The sliding of the whole gun to the rear by means of the mechanism of the brake is controlled, as to speed and time, by springs, by compressed air, by compressed oil, etc., either all together or in combinations of two or three of these agencies; so that the whole recoil energy is absorbed and the rearward action of the gun brought to rest in a fraction of a second and in but a very few inches of travel. The strains are distributed from the recoil mechanism to the fixed portion of the carriage that is necessarily anchored to the ground by means of spades, which the recoil force of each shot sets more firmly into the ground, so that the whole apparatus is thus steadily held in place for successive shots.
In mobile artillery, again, rapid firing is a prime essential. The 75-millimeter gun of modern manufacture is capable of being fired at a rate in excess of 20 shots a minute—that is, a shot every 3 seconds.
Rarely however, is a gun served as rapidly as this. The more usual rate of fire is 6 shots a minute or 1 about each 10 seconds, and this rate of fire can be maintained in the 75-millimeter gun with great accuracy over a comparatively long period.
The larger guns are served at proportionately slower rates, until as the calibers progress to the 14-inch rifles, which have been set up upon railway mounts as well as on fixed emplacements for seacoast defense, the rate of fire is reduced to one shot in three minutes for railway mounts, and to one shot a minute for seacoast mounts, although upon occasions a more rapid rate of fire can be reached.
Under rapid fire conditions, the gun becomes very hot, owing to the heat generated by the combustion of the powder within the gun at pressures as high as 35,000 pounds per square inch or more, which are generated at the moment of fire. This heat is communicated through the walls of the gun and taken off by the cooling properties of the air. Nevertheless, the wall of the gun becomes so hot that it would scorch or burn a hand laid upon it. The rapid fire and heating of the gun lessens the effective life of the weapon, due to the fact that the hot powder gases react more rapidly on hot metal than they do upon cold metal; hence a gun will last many rounds longer if fired at a slow rate than if fired at a rapid rate.
It may be helpful to keep in mind throughout that the sole purpose of a gun is to fire a projectile, as was stated at the very beginning of this chapter. All other operations connected with the life of a gun, its manufacture, its transportation to the place where it is to be used, its aiming, its loading and all its functions and operations are bound up in the single purpose of actually firing the shot.
Consider now for a moment, the life of, let us say, one of the 14-inch guns.