There is considerable disagreement as to who invented the device for controlling the fire of a machine-gun so as not to strike the blade of the propeller, but it is admitted that the Germans were the first to make any extensive use of it, introducing it on the Fokker monoplanes, which caused so much damage on the Western Front in 1915. Shortly thereafter the Allies adopted similar devices. When the United States entered the war neither the Ordnance Department nor the Aviation Section of the Signal Corps had had any experience worthy of the name with aircraft guns. And if they were ill-informed on the subject of guns, they were appallingly ignorant on the subject of gun controls. A few months of study and experiments served to materially increase the War Department’s knowledge along these lines, however, and by the time the planes were ready to receive the guns we had adopted a device known as the Constantinisco control. I should explain, perhaps, that there are two distinct types of gun control, both of which were in use when hostilities ceased. One is hydraulic, the other mechanical. The operation of both types is somewhat similar. In each case a cam mounted on the shaft of the engine actuates a plunger which in turn operates the rest of the mechanism. In the mechanical gun control the impulse of the cam is transmitted to the gun through a series of rods, causing the gun to fire at the exact moment when there is no propeller-blade in front of the muzzle. In the hydraulic type the impulse of the cam is transmitted to the gun through a system of copper tubes containing oil under high pressure. The hydraulic control, known as the Constantinisco, was adopted for use on American planes, particularly the De Havilland 4, which carries two fixed Marlins, each firing at the rate of 650 shots a minute. By employing the maximum rate of fire, 1,300 shots could be fired in a minute through the blades of the propeller, which would make 1,600 revolutions in the same space of time—without the blades being struck by a single bullet.