It was 75 years ago Oct. 14 that U.S. Air Force Capt. Chuck Yeager climbed into a rocket plane he named "Glamorous Glennis" for his wife and did what many thought was the impossible: He broke the sound barrier. This page looks at Yeager's accomplishment, what causes sonic booms and compares Yeager's X-1 craft to the top speeds of other fast-flying airplanes such as the Concorde, the F-15 Eagle, the SR-71 Blackbird and the X-15.