It Was Only A Demonstration - A simulated atomic bomb explosion mushrooms over Philadelphia's International airport today during second-day program of the National Aircraft show but it gave the folks at home an idea of a bomb explosion. The bomb was detonated in the center of the field during a mock assault -- bat It did not, contain an atomic warhead. More than 60,000 persons watched fliers from four military branches stage flight and ground demonstrations. September 04, 1955. (Photo by AP Wirephoto).