After an exhausting session with Victoria's Secret Police,
BackToNormal blurted out:

Was half paying attention to a TV doco on the Dambusters a few mins ago
and thought I heard the narrator say the Earthquake bomb designed by
Barnes Wallis broke the sound barrie on its way down.
Comments anyone?

Try http://www.grc.nasa.gov/WWW/K-12/airplane/termv.html