The advantage of these machine guns over Gatling’s lay not only in the saving of human labor, but in the fact that a single barrel was employed in place of ten, thereby greatly reducing the weight of the gun. But a serious handicap was encountered in the heat developed by the burning powder. Dr. Gatling, by using ten barrels, could let nine be cooling while the tenth was discharging, but even he found it necessary to place a water jacket about half the length of the barrels. In the Maxim machine gun a large water jacket enveloped the whole length of the barrel and when the gun was firing continuously at a moderate rate the 7½ pints of water contained in the water jacket would come to a boil inside of a minute and a half, and thereafter more than a pint would be evaporated each minute of firing, or about a pint and a half per thousand rounds. The necessity of using water-cooling added considerably to the weight of the gun and made it occupy in the service an intermediate place between the shoulder rifle and the big gun.

Another method of cooling was to use a barrel with a large outer diameter and depend upon the radiation of heat from the outer surface to prevent overheating. This was later improved by putting flanges on the outer surface of the barrel, so as to increase the radiating surface, in the same way that the cylinders of a motorcycle are kept cool. The barrel was made easily detachable and a spare one provided, so that as soon as the barrel grew excessively hot it could be removed and replaced with a cool barrel. The fault of overheating is not that it might explode the cartridge prematurely but that the bore will be enlarged by heat expansion so that the bullets will not take the rifling and will come out of the barrel as if from a smooth-bore gun. In a test of a Hotchkiss machine gun which was fired continuously the expansion was sufficient at the end of four minutes to make the course of the bullets very uncertain and in seven minutes the bullets, emerging without any spin, tumbled over and over and failed to carry more than three hundred yards.

A GUN THAT FANS ITSELF

The next marked step in the development of the machine gun was to make it fan itself and thus keep its barrel cool. Col. I. N. Lewis designed a gun operated by gas pressure somewhat on the principle of the Colt gun and around the barrel he fitted sixteen deep flanges or fins of aluminum that ran lengthwise of the gun. Around these fins he fitted a casing, thus forming 16 long narrow chambers about the barrel. The casing was open at the breech end, but at the outer end was contracted into a narrow mouthpiece that extended beyond the muzzle. The mouthpiece was so formed that as the bullets passed through it they sucked air through the chambers, thereby cooling the gun. The air travels through the casing at the rate of about seventy miles per hour.

This design permitted Col. Lewis to build a very light gun. Its total weight was but 25½ pounds and it could be handled by a single man if the muzzle was supported on some sort of a rest. It represented a marked step toward a shoulder machine gun which would increase enormously the efficiency of infantry equipped with this weapon. The difference between rifle fire and machine-gun fire has been likened to the difference between trying to hit a tin can with a stone and with a stream of water from a hose. In the latter case the hose may be raised or lowered to correct the course of the stream and bring it to bear on the target. In the same way by watching the effect of the machine-gun bullets the leaden stream may be corrected to bring it directly upon the target. The advantages of a weapon such as this, which may be fired from the shoulder or from the hip, are perfectly obvious.

As the war was nearing its end John M. Browning produced two machine guns, one a water-cooled heavy model fired from a stand. The total weight of this gun was 34½ pounds and with the water jacket empty it weighed but 22½ pounds. It was operated by the recoil of the gun, but the mechanism was greatly simplified and there were but few parts. These could be taken apart and replaced with new ones in a minimum of time in case of breakage. The other gun was a shoulder rifle weighing only 16 pounds, which carried a clip of twenty cartridges. These could be fired singly or in rapid succession in the space of two and a half seconds. Only a second was required to replace the empty clip with a filled one. No special cooling apparatus was provided because it was not likely that a shoulder rifle would be fired long enough at a time to become excessively heated.

POCKET-SIZED MACHINE GUN

The latest development in machine guns is a pocket edition weapon—a firearm weighing only 7 pounds and measuring but 22 inches over all. This little gun which is too small to be classed as a rifle and yet rather large for a pistol, has two grips so that it may be fired from the waist line, and it may be fitted with a gun butt so that it may be fired from the shoulder. It operates at the astounding rate of 1,500 shots per minute or three times the speed of the average machine gun. The cartridges are fed either from a box magazine containing 20 rounds or from a drum-shaped magazine loaded with 50 to 100 cartridges. The operating mechanism of this gun is entirely different from anything produced heretofore and depends upon a discovery made by Commander Blish of the United States Navy. He found that a wedge of a certain angle will hold a breechblock closed against the pressure of an exploding cartridge while the pressure is high, but will slide when the pressure falls. Apparently at first the adhesion due to friction is too great to permit the wedge to move, but the adhesion falls off more rapidly than the pressure does and a point is reached at which the wedge yields to the pressure. In the “submachine” gun, as the new weapon is called, the barrel (or rather an extension of the barrel) and the receiver, in which the operating mechanism is contained, are locked together by a wedge. The wedge slides in slots set at an angle of 80 degrees with the axis of the barrel. When a cartridge is fired the wedge remains fast while the bullet is traveling through the bore, but when it emerges and the pressure of the gases falls off the wedge slides, unlocking the breech mechanism. The gun is remarkable for its simplicity and the fewness of its parts. It has been adopted by the Police Department of New York City.

ARTILLERY VS. ARMOR

As has been stated above, gunpowder was first introduced in warfare not for the purpose of destroying men, but for smashing city walls and fortifications, so that infantry could pour through the breeches made by the heavy stone or iron projectiles. As artillery grew more powerful and the aim more accurate walls of masonry gave way to earthworks and to masses of concrete and armored steel. However the World War demonstrated the impossibility of building any fortifications above ground that would stand up against modern high-powered guns.