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Tracer ammunition (tracers) are bullets or cannon caliber projectiles that are built with a small pyrotechnic charge in their base. Ignited by the burning powder, the pyrotechnic composition burns very brightly, making the projectile trajectory visible to the naked eye during daylight, and very bright during nighttime firing. This enables the shooter to make aiming corrections without observing the impact of the rounds fired and without using the sights of the weapon. When used, tracers are usually loaded as every fifth round in machine gun belts, referred to as four-to-one tracer. Platoon and squad leaders will load some tracer rounds in their magazine or even use solely tracers to mark targets for their soldiers to fire on. Tracers are also sometimes placed two or three rounds from the bottom of magazines to alert the shooter that their weapon is almost empty. During World War II, aircraft with fixed machine guns or cannons mounted would sometimes have a series of tracer rounds added near the end of the ammunition belts, to alert the pilot that he was almost out of ammunition. More often, however, the entire magazine was loaded four-to-one, on both fixed offensive and flexible defensive guns, to help mitigate the difficulties of aerial gunnery. Tracers were very common on most WWII aircraft, with the exception of night fighters, which needed to be able to attack and shoot down the enemy before they realized they were under attack, and without betraying its own location to the enemy defensive gunners. The United States relied heavily on tracer ammunition for the defensive Browning M2 .50 caliber machine guns on their heavy bombers such as the B-24 Liberator, but they found that during deflection shooting, gunners who tried to aim using the tracers rather than the sights ended up not "leading" the enemy aircraft enough and missing, because of an optical illusion that made it appear that the tracers were striking the aircraft, when it reality they were passing significantly behind it. This proved true of fixed forward firing guns as well. In some cases, gunners were ordered not to use tracer ammunition at all, but in the end, with greater emphasis during training on using the sights and not trusting the tracers, the problem was solved to a large degree. Tracer rounds can also have a mild incendiary effect, and can ignite flammable substances on contact, provided the tracer compound has started burning and is still burning on impact. == History == Before the development of tracers, gunners relied on seeing their bullet impacts to adjust their aim. However, these were not always visible, especially as the effective range of ammunition increased dramatically during the later half of the 19th century, meaning the bullets could impact a mile or more away in long range area fire. In the early 20th century, ammunition designers developed "spotlight" bullets, which would create a flash or smoke puff on impact to increase their visibility. However, these projectiles were deemed in violation of the Hague Conventions prohibition of "exploding bullets."〔Barnes, Frank; Skinner, Stan. ''(Cartridges of the World ).'' DBI Books, Inc., 1993 (pages 425-6).〕 This strategy was also useless when firing at aircraft, as there was nothing for the projectiles to impact on if they missed the target. Designers also developed bullets that would trail white smoke. However, these designs required an excessive amount of mass loss to generate a satisfactory trail. The loss of mass en route to the target severely affected the bullet's ballistics. The United Kingdom was the first to develop and introduce a tracer round, a version of the .303 cartridge in 1915.〔"(History of the .303 British Calibre Service Ammunition Round )." ''dave-cushman.net,'' 10 July 2001.〕 The United States introduced a .30-06 tracer in 1917.〔Barnes, Frank; Skinner, Stan. ''(Cartridges of the World ).'' DBI Books, Inc., 1993 (page 426).〕 Prior to adopting red (and later, other color) bullet tips for tracers, American tracers were identified by blackened cartridge cases. Tracers proved useful as a countermeasure against Zeppelins used by Germany during World War I. The airships were used for reconnaissance, surveillance and bombing operations. Normal bullets merely had the effect of causing a slow leak, but tracers could ignite the hydrogen gasbags, and bring down the airship quickly. In World War II U.S. naval and marine aircrew were issued tracer rounds with their side arms for emergency signaling use as well as defense.〔Edwards Brown Jr., ''DCM Shopper's Guide'', The American Rifleman, (April 1946).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tracer ammunition」の詳細全文を読む スポンサード リンク
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