After the shocking assassination of John F. Kennedy in 1963, America had to move fast to get a new President into office. That President was Lyndon B. Johnson. There wasn't even time to get him to a suitable location for the ceremony, and so it happened on the plane.
The resulting picture is one of the most famous in American political history, and was taken on Air Force One on November 22nd, 1963. Jackie Kennedy is by the new President's side.