One of the first acts of the Ordnance Department was to send an officer to visit the ammunition factories of France and England to study the methods of manufacturing these special types of bullets. These friendly nations willingly gave us full information at first hand with respect to this complicated manufacture, which we were thus enabled to begin in September, 1917. Special machinery was required for loading the tracer bullet and also for producing the incendiary projectile. We adopted British practice for both of these. We ourselves were well equipped to begin the production of armor-piercing bullets, for which we had previously solved the problems of design; yet the production of metals to be used in this missile required some further experimental work. By February, 1918, however, our production of armor-piercing bullets was well under way and by the time the war came to an end we had produced nearly 5,000,000 of them. The tracer bullet which we manufactured contained a mixture of barium peroxide and magnesium and in flight burned with the intensity of a calcium light. These bullets were principally used by machine gunners of aircraft, since in the air it is impossible to tell where machine-gun projectiles are going unless there is some device enabling the gunner to see the trajectory of the bullets. This is done by inserting tracer bullets at intervals in the belts of cartridges fed into the machine gun. The common conception of a tracer bullet is one that leaves a trace of smoke in its flight; whereas the truth is that our tracer and the British tracer were practically smokeless, the gunner observing the direction of aim by following the bright lights of the tracer bullets with his eye. These lights were plainly visible in the brightest sunlight. Although the slight quantity of the flaming mixture burned but a few seconds, it was sufficient to trace the flight for 500 yards or more from the muzzle of the machine gun. The tracer bullet consisted of a cupronickel shell, the nose of which contained a leaden core to balance the bullet properly. The rear chamber of the bullet held a cup containing the mixture of barium peroxide and magnesium. The rear end of the bullet was left slightly open, and through this opening the mixture was ignited by the hot flame of the propelling powder discharge.