[cyberia]

It was a common practice on fighter planes to load every 5th round with a tracer to aid in aiming.

It was later discovered this was a mistake on a number of levels:

Tracer rounds had different ballistics so (at long range) if your tracers were hitting the target, 80% of your rounds were missing.

Worse yet, the tracers instantly told your enemy he was under fire and from which direction.

To make matters ever worse, the practice of loading a string of tracers at the end of the belt to tell you that you were out of ammo was a sure sign to enemy planes you were vulnerable.

Units that stopped using tracers saw their success rate nearly double and their loss rate go down a third.