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Rh The Vickers Machine-Gun. A more conservative effort toward the reduction of weight resulted in the production of the Vickers light machine-gun (afterwards called the Vickers machine-gun) by Vickers, Ltd., in 1910. The mechanism of this gun is essentially the same as that of the Maxim, formerly produced by the same com- pany, but the gun is considerably smaller, and the weight has been reduced by one-half. This reduction in size and weight was accom- plished without sacrifice, for the Vickers is superior to the old Maxim not only in portability and ease of concealment but also in durability and reliability, while its volume of fire and steadiness of mounting are the same. The weight of the gun is 38 lb., and that of the tripod is 35 pounds. The gun has a corrugated steel water-jacket holding 7j pt., and is fed from a belt holding 250 rounds of ammunition. The Vickers gun became the standard of the British army, and, after a series of trials, it was adopted by the United States in 1915 to supersede the Benet-Mercie as the service gun. It was also adopted by the Russians. During the World War the bulk of the machine- guns in the British army were of the Vickers type, and many thou- sands of Vickers guns were used by the American troops.

The Lewis Gun. The outbreak of the war in 1914 forced upon Great Britain the necessity of rapidly supplementing the small stock of machine-guns then on hand. In this emergency a portable air- cooled machine-rifle, invented by Col. I. N. Lewis, a retired officer of the U.S. army, was adopted and manufactured in quantity. In size and weight the Lewis gun resembles the Benet-Mercid and, like it, is gas-operated ; but it differs in the methods of feeding and cooling. The cartridges are fed to the gun in flat disc-shaped magazines, each holding 47 rounds. The characteristic method of cooling employed on this gun is known as the positive air-cooling system. There is an aluminium radiator surrounding the barrel, and encased in a sheet- metal jacket which extends beyond the muzzle of the gun and is open at both ends. During the firing of the piece, the blast of gases from the muzzle induces a draft of air through the radiator casing. _ This rapidly moving column of air passes over fins on the aluminium radiator and cools the gun almost as effectively as a water-jacket would. As the war progressed, the Lewis guns became extremely popular, and were used in a very effective manner. Owing to their portability and the absence of such encumbrances as tripods and water-supply, it became possible to use them for direct fire in the most advanced positions. However, it was soon recognized that their limited fire capacity and lack of a steady mount rendered them unsuitable for overhead supporting fire, indirect fire, and barrage work, all of which functions were fulfilled admirably by the Vickers guns from positions farther in the rear.

American Controversy. -In 1916 the United States, which had become involved in a threatening situation on the Mexican border, experienced a shortage of machine-guns. None of the Vickers guns under manufacture had been delivered, so, in order to meet the immediate need for guns on the border, several hundred Lewis guns, chambered for the British cartridge, were purchased, together with a supply of ammunition. About this time Congress made an appro- priation of $12, 000,000 for the purchase of machine-guns. Imme- diately afterwards a sharp controversy arose as to the relative merits of the Lewis machine-gun and of the service automatic weapons (Benet-Merci6 and Vickers). To settle this controversy the Secre- tary of War appointed a board, consisting partly of army and navy officials of high rank and partly of civilians, to go deeply into the subject of the proper machine-gun policy. After extended sittings this board rendered a report which for the first time in the United States called attention to a fact which the machine-gun tactics developed in the British army during two years of war should have rendered plainly apparent long before. This was the fact that the heavy machine-gun and the light machine-gun or machine-rifle (Lewis gun) were not interchangeable in function, and that a certain proportion of each type should be supplied. The board defined the two types under consideration as (i) heavy type, relatively heavy, with substantive tripod mount, effectively cooled for continuous fire, fed from a belt ; and (2) light type, comparatively light weight, highly portable, without tripod mount, air-cooled, fed from a magazine. The board recommended that the relative proportion of these weapons to be purchased should be two of the light type to one of the heavy. It also reported that the Vickers machine-gun " fulfilled to a high degree the requirements of the service for a machine-rifle of the heavy type. The board is not able at this time to recommend a machine-rifle that will fulfil the requirements of the military for a machine-rifle of the light type." The board recommended the immediate purchase of 4,600 Vickers machine-guns, and made recommendations for a test to be held in May 1917. A notice was published giving the date of the proposed test and inviting manu- facturers and inventors to submit weapons for trial. Just before the date set for the test the United States declared war on Germany, and, as a result, emergency orders were placed for a large quantity of Lewis guns, and for several thousand Colt guns made by the Marlin-Rockwell Co. who were building these guns in large quanti- ties for Russia. In May 1917 the Machine-Gun Board held the official test that had been advertised some months before. The Vickers and Lewis guns proved efficient, but the most marked superiority was shown by a new gun introduced by Mr. John M. Browning, the inventor of the Colt machine-gun and of many rifles and automatic pistols. The standard endurance test was the firing

of 20,000 rounds. Mr. Browning fired this test without stopping to clean his gun, and with so little trouble that he was ordered to continue firing until some trouble developed. The gun fired over 39,000 rounds before the first breakage occurred. In order to verify this phenomenal performance, the inventor was required to fire a duplicate gun, which completed the 2q,ooo-round test in 48 minutes and 12 seconds with only three stoppages, all of which were due to defective ammunition. In size, weight, and general appearance the Browning gun resembles the Vickers, but it has an entirely different mechanism. An examination of the mechanical construction of this gun revealed a remarkable simplicity from a manufacturing point of view. This gun showed such promise that, before proceeding with the trials of the remaining weapons before it, the Board rendered a preliminary report recommending that the manufacture of the Browning gun in quantities be undertaken at once. The recom- mendations of the Board were followed, and several large arms factories were started on the task of producing the new gun in the shortest possible time. Thanks to the simplicity of the design, the manufacturers who were entrusted with the task of producing Browning guns were enabled to turn out enormous quantities of them during the war.

The Browning Automatic Rifle. After the test of his heavy machine-gun Mr. Browning submitted a weapon weighing only 15 lb., but at the same time capable of automatic fire from detach- able magazines holding either 20 or 40 rounds. This rifle passed a highly successful test and was ordered adopted. It was at once recognized that this was a new and distinct type of gun, as its fire- power was nearly equal to that of the machine-rifle type (Lewis and Benet-Mercie), while its weight was but little more than half as great, a fact which enabled it to be fired from the shoulder or hip with ease. The success of this weapon led to the immediate elimination of the intermediate type from the armament of the ground forces of the United States, and the assignment of the Lewis guns to the air service, to be stripped and mounted on aeroplanes as flexible guns.

As a result of the introduction of the light Browning machine- rifle, as it was at first called, and of the Chauchat, a gun somewhat similar in general type introduced by the French, it became desirable to adopt terms to define more clearly the different classes of auto- matic weapons. In order to accomplish this purpose, an order was issued by the War Department assigning to the heavy type of auto- matic weapon the designation " machine-gun "; to the intermediate type (Lewis, Benet-Mercie), the designation " machine-rifle "; and to the light type (Browning, etc.), the term " automatic rifle." The term " semi-automatic rifle " was assigned to self-loading weapons weighing 10 lb. or less, designed to take the place of the magazine- rifle. During the remainder of this article the terminology given will be adhered to, and as the lighter weapons are separately described in the article on RIFLES AND LIGHT MACHINE-GUNS the machine-gun only will be considered here.

Aircraft Machine-Gun. Early in the World War, the application of machine-guns to aircraft began by the improvised mounting of the regular ground-type guns on aeroplanes. Soon, however, the increasing use of machine-guns in aerial warfare developed two standard systems of mounting guns in aircraft. According to the method of mounting them, aircraft guns are either " flexible " or " fixed." In flexible mountings the guns are pivoted so that they may be freely swung or pointed in any direction by the gunner. Flexible guns are usually mounted in the rear cockpit, but in some large bombing airplanes they have been mounted in the nose, or in the fuselage to shoot through a shutter in the bottom. The standard flexible gun in the Allied services was the Lewis, which, for aircraft use, was stripped of the cooling system and was fitted with magazines of extra capacity holding 97 shots. These guns were frequently mounted in pairs, with the idea of shooting both guns at once and thus increasing the volume of fire. " Fixed " aeroplane guns are usually mounted either above or beside the engine, and are perma- nently pointed in one direction, which is straight ahead. Conse- quently, in order to aim the guns, it is necessary to turn the whole aeroplane so that it is pointing at the enemy. For this reason these guns are operated by the pilot. Because the guns fire straight ahead, it is necessary for them to shoot through the arc swept by the pro- peller blades. In order to avoid damage to the propeller, fixed guns are synchronized so that the shots go between the blades. This synchronization is accomplished by having the trigger of the gun operated from a cam on the engine shaft. This cam and the firing mechanism, which it operates, are so timed that the gun will be fired only when the propeller blades are in such a position that the shots will not strike them. The firing mechanism is so arranged that it is inoperative except when it is thrown into gear by a lever situated for convenient manipulation by the pilot. Synchronized guns are generally of the type fed by a belt. Those used by the Americans and the British usually employ link belts instead of woven fabric belts. The metallic links are pinned together by the cartridges themselves, and as the cartridges are pulled out of the belt in being fed through the gun the belt disintegrates into a series of separate links. This avoids the complications and dangers incident to the use in aircraft guns of fabric belts which have to be reeled up as they leave the gun in order to avoid having them trailing in the wind and perhaps flying into the pilot's face or interfering with the controls. Owing to the fact that the fleeting opportunities of