The first Boeing jetliner to break the sound barrier was the Boeing 707. While the Boeing 707 was not specifically designed to break the sound barrier, it was capable of doing so under certain conditions. On October 15, 1958, a Boeing 707-120, known as the Boeing 707-120B, piloted by Tex Johnston, achieved supersonic speeds during a demonstration flight over the Seattle area. During a low-level flyby, Johnston executed a barrel roll with the aircraft, demonstrating its maneuverability and breaking the sound barrier in the process. This event, known as the "Tex Johnston's barrel roll," is a well-known moment in aviation history.