Allied Bombers Stopped German Fighters With This Bullet

YouTube / WWII US Bombers
During World War II, U.S. bombers sought effective ways to deter Axis aircraft from attacking their formations. One such method involved the use of M21 headlight tracers.
Benefits of Tracers
Tracers, when included in ammunition belts, have a noticeable psychological impact on enemy pilots.

Traditionally, every fifth round in a belt was a tracer, creating visible streams of light that could intimidate attacking aircraft. This visual effect often caused enemy pilots to break off their attacks prematurely, reducing the number of successful strikes on U.S. bombers.

However, the effectiveness of tracers was not universally accepted.
Combat Impact
According to a 1944 Intelligence Office document from the 66th Fighter Wing, a captured German pilot revealed that tracers did not deter their attacks. In fact, they sometimes welcomed tracers because they highlighted weaker, less defended areas of the formation.

Removing tracers posed its own challenges. Gunners had to be retrained to ensure they could still accurately target enemy aircraft without the visual aid of tracers.
Despite this, many gunners reported that tracers distracted and frightened attacking pilots, potentially disrupting their attacks even if the bullets did not hit their targets.
Development of M21 Tracers
The M21 headlight tracer was an enhancement of the standard M1 tracer, featuring a 100% igniter compound instead of a mix of tracer and igniter compounds. This made the M21 tracers three times brighter than the M1s.

By the end of 1944, M21 tracers were widely adopted, and field reports suggested they were effective in causing German interceptors to break off their attacks sooner, leading to less aggressive assaults on bomber formations.

Post-War Reflections
Post-war surveys and interviews provided mixed feedback on the use of tracers.

While some German pilots admitted that tracers highlighted the formation’s vulnerable points, they were not as intimidated by them as U.S. bomber gunners believed. Consequently, the use of tracers declined after the war.