The scaled-down prototype, nicknamed the "Baby Boom", broke the sound barrier for the first time during a test flight over the Mojave Desert in California in late January. The small jet, officially called XB-1, reached an altitude of 35,000 feet before accelerating to Mach 1.1 (844mph) – "10% faster than the speed of sound", said Sky News.

Boom Supersonic’s XB-1 creates a sonic boom inaudible from the ground below when flying at the exact right speed and altitude.

Aerospace startup Boom says they've proven quiet supersonic flight is possible with their passenger airplanes after a successful second test flight.