The sound barrier refers to the sharp increase in aerodynamic drag which aircraft experience when approaching the speed of sound. Chuck Yeager was the first to conquer this barrier, which requires more than just great flying skill. It also requires rigorous aircraft design.

For as aircraft approaches Mach speed, airflow over some plane parts exceeds the speed of sound, creating shockwaves which force the craft to nose down. Only planes designed to overcome this will be capable of making it to 767 miles per hour.

While Yeager is credited with being the first to do this, a few alternate histories hold that others accomplished it before he did.

Some think German World War II pilots managed this, but captured intelligence documents make no mention of this having happened.

Still, tales persist that Messerschmit Komet pilots were the first to break the sound barrier. Heini Dittmar is one name associated with this supposed accomplishment. However, this was never referenced until a 1990 book, the contents of which contain no documentation from the 1940s, when these flights are said to have taken place.

Besides, as Skeptoid’s Brian Dunning noted, the Komet’s design would have made reaching such a speed impossible. He wrote, “The Komet had fabric-covered elevons on the trailing edge of the delta wing, which would always be shock stalled.”

Another key item is the imprecise nature of airspeed indicators of the time. Aircraft designed for below-sonic speed will in all likelihood yield unreliable readings because of the shockwaves. By contrast, aircraft designed to be supersonic employ a Mach indicator, which Dunning explains corrects for static air pressure.

There are two other supposed pre-Yeager Mach speed flights cited by alternate historians, both taken by civilian test pilot George Welch. He putatively took an XP-86 fighter prototype and, in a powered dive from 35,000 feet, broke the sound barrier. Anecdotal stories say that a sonic boom was heard on the ground.

But author Robert Kempel contends that for Welch’s aircraft to break the sound barrier with an J35-C-3 engine would be impossible, and Welch never himself claimed to have made it to Mach speed.