It was a common practice on fighter planes to load every 5th found with a tracer round to aid in aiming. That was a mistake. The tracers 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. Worst of all was the practice of loading a string of tracers at the end of the belt to tell you that you were out of ammo. That was definitely not something you wanted to tell the enemy. Units that stopped using tracers saw their success rate nearly double and their loss rate go down.