What incident 55 years ago demonstrated the need for a dedicated air traffic control call sign for the aircraft carrying the President of the United States as Air Force One?
If any of you amateur radio operators are tooling around in the ham universe and come across a very serious voice informing you that "Cadillac One is inbound," we'd advise closing the channel -- especially if you live in the vicinity of any major political institutions. There's at least a fair chance you've tapped into U.S. Secret Service communications because Cadillac One is the informal nickname of the U.S. Presidential State Car, the limousine that carries the American Commander-in-Chief around.
If the U.S. National Security Agency finds you eavesdropping on Presidential security comms, they'll either be very displeased or offer you a job. Either way, your life will likely become much more interesting in very short order. And we're not limiting this advice to mere U.S. residents either, as Cadillac One often gets airlifted to other countries where the U.S. President is making an appearance. The same goes for (ironically) Marine One, one of a squadron of military helicopters used to transport the President by air over moderate distances. Indeed, by some measures, Marine One and the so-called Cadillac One exist largely to ferry the President back and forth to Air Force One, the specially modified jumbo airliner that serves as a flying miniature White House.
(Yes, calling a jumbo airliner "miniature" seems strange, but the 4,000 square feet of cabin space available on the modern Air Force One is positively tiny compared to the 55,000 square feet available in the actual White House.)
While any plane carrying the President of the United States is, by protocol, designated Air Force One, when most people use that term, they're referring to one of two modified Boeing VC-25s, which are variants on the Boeing 747-200B. With their signature blue-and-white livery -- developed by designer Raymond Loewy to mimic the typeface of the Declaration of Independence -- these jets are known worldwide as symbols of the American Presidency. However, when the U.S. President isn't aboard, these craft are often referred to by either their tail numbers -- 28000 or 29000 -- or by a conventional flight number, just like any other aircraft traveling through controlled airspace.
Moreover, prior to 1953, even if an aircraft was carrying a U.S. President, it was still known by its standard Air Force flight number. It wasn't until that year that anyone discovered a need for the call sign Air Force One -- and it was a very pressing need, at that.
WHY WAS THE U.S. PRESIDENTIAL AIRCRAFT GIVEN THE CALL SIGN AIR FORCE ONE?