Lyndon B. Johnson took the oath of office to become President of the United States on an airplane (specifically, on Air Force One, the presidential airplane) sitting on the tarmac at the airport (Love Field) in Dallas after Pres. John F. Kennedy was assassinated in November of 1963.
Johnson had been in a separate car in the same motorcade as Kennedy and so he was right there to take the oath of office that same night (November 22). His oath was administered by Sarah T. Hughes, who was a US District Court judge in Texas.
Lyndon B. Johnson (1908-1973) was president of USA from 1963 to 1969. He served as vice president under John F. Kennedy, and was sworn in as President on November 23, 1963, just about two hours after assassination of President Kennedy. He was sworn inside a Presidential Airplane, traditionally called "Air Force One", parked at Love Field Airport in Dallas. He was sworn in by a Federal Judge, Sarah T. Hughes. President Johnson is the first and the only president to have been sworn in on Texas soil and by a woman.