Tracer ammunition

Tracer ammunition contains a pyrotechnic element that emits light as a projectile travels, making its trajectory visible for aiming or signaling.

Pyrotechnic composition: A mixture that produces heat, light, gas, or sound through a self-sustaining chemical reaction. Tracer elements use a pyrotechnic reaction to emit visible light during flight.
Aiming: The process of aligning a weapon with a target to direct a projectile toward it. Shooters use visible tracer paths to observe and adjust the direction of fire.
Ball ammunition: Standard ammunition with a non-specialized projectile intended for ordinary target engagement. Unlike tracer ammunition, it does not contain a light-emitting element.
Muzzle signature: The visible, infrared, or acoustic emissions produced when a firearm is discharged. Tracer light adds a conspicuous in-flight signature to the flash and sound of firing.
World War I: A global war fought from 1914 to 1918, chiefly between the Allied and Central Powers. Tracer ammunition emerged during this period to help observe machine-gun fire.
Projectile (firearms): An object expelled from a firearm by the pressure of expanding gases. The tracer element is built into a projectile that follows a ballistic path.
Fire control: The methods and equipment used to direct weapons accurately at a target. Tracers provide visual feedback for correcting weapon fire.
Armor-piercing ammunition: Ammunition designed to penetrate armor or other hard protective materials. Its defining function is penetration, unlike the trajectory visibility sought from tracers.
Counter-battery fire: Fire directed against an enemy's artillery or mortar positions. Visible trajectories can help opposing forces infer a firing position and return fire.
Lewis gun: A light machine gun developed in the early twentieth century and used by several armed forces. Its use in aircraft created a need to observe and adjust fire in flight.

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Cartridge (firearms)Related: A tracer projectile adds a visible trajectory cue to a cartridge’s function.