When the United States entered the war the Vickers was the only type of fixed gun in use on either English or French planes and was used on all the planes which General Pershing bought in France. When the Equipment Division of the Signal Corps faced the machine-gun situation in September, 1917, it was alarmed to find that the entire production of Vickers in the United States had already been contracted for to supply the imperative requirements of the infantry. There was another gun on the market at this time, however—the Marlin—and toward its development for aircraft use the officers of the Signal Corps bent all their energies. Though the Marlin was adopted in the face of violent opposition, it resulted in providing sufficient fixed guns to arm the American planes, the wisdom of the action being proved by the fact that up to the time of the Armistice no other fixed guns were ready for delivery. The Marlin has been adapted to all American-built planes which carry fixed or synchronized guns, over 37,000 having been produced up to December, 1918. This gun shoots .30-calibre ammunition at the rate of 600 to 650 shots a minute and is fed from a belt of the disintegrating metal-link type. In December, 1917, the first order was placed for Lewis aircraft guns, over 39,000 of them being delivered to the American Air Service within the following twelvemonth. A notable improvement in the aircraft model of the Lewis gun was an increase in the depth of the magazine pan, so that each magazine holds 97 cartridges instead of 47 as previously. The Browning aircraft machine-gun was just coming into production when the war ended. This weapon embodies the best features of every known machine-gun and would probably have replaced all other types in use. It is a belt-fed gun of the recoil type—both the Marlin and Lewis are gas-operated—is as near fool-proof as a machine-gun can be made, and has the amazing rate of fire of 950 shots a minute. Of it the inventor is said to have remarked: “If it had four more parts it could play a tune; if it had seven more parts it could talk.” The ammunition for fixed aircraft guns, such as the Marlin and Browning, is carried in belts containing a maximum of 500 rounds. In the earlier days of the war these belts were of woven web, but it was found that taking care of them, when empty, in the limited space of the fuselage, was always a source of annoyance and not infrequently a source of danger to the aviator. To remedy this a belt was designed and furnished to the American Expeditionary Forces which consisted of small metallic links held together by the cartridges themselves. As the gun fires, the links drop apart, chutes being provided so that they fall clear of the airplane. Another minor though interesting feature of aircraft armament is the small electric heater which is now provided for the purpose of keeping the gun warm and thus preventing the oil from congealing in high altitudes.