Here a quick blurb from the internal Boeing news website highlighting this event...
Boeing Dash 80 rolled out 50 years ago today
On May 14, 1954, thousands of people at the Renton, Wash., facility witnessed the rollout of the 367-80 aircraft, more commonly known as the Dash 80. That airplane helped lead aviation into the jet age as prototype of the 707 -- the first commercially-successful jet-powered passenger plane -- and the U.S. Air Force's KC-135 aerial-refueling aircraft. The Dash 80, restored by Boeing employees and retirees, is now on display at the Smithsonian's Steven F. Udvar-Hazy Center in Chantilly, Va.