How did tracer devices help antiaircraft gunners correct their fire?

Tracer devices were essential for antiaircraft gunners because they provided a visual method to correct fire against high-speed targets. By incorporating these devices into projectiles, the shells left a visible trail of flame and smoke as they traveled through the air.1

This trail allowed gunners to observe the shell's actual trajectory relative to the target. Because early antiaircraft guns faced the difficult challenge of hitting targets moving in three planes at high speeds, these visual indicators helped operators adjust their aim to compensate for the target's movement and the time required for the shell to reach its destination. This technique was particularly significant during World War I, when visual correction was a primary means of managing the complex fire-control problem.1