<P> The primary means of long distance air travel for the president is one of two identical Boeing VC - 25 aircraft, which are extensively modified Boeing 747 airliners and are referred to as Air Force One while the president is on board (although any U.S. Air Force aircraft the President is aboard is designated as "Air Force One" for the duration of the flight). In - country trips are typically handled with just one of the two planes, while overseas trips are handled with both, one primary and one backup . The president also has access to smaller Air Force aircraft, most notably the Boeing C - 32, which are used when the president must travel to airports that cannot support a jumbo jet . Any civilian aircraft the President is aboard is designated Executive One for the flight . </P> <P> For short distance air travel, the president has access to a fleet of U.S. Marine Corps helicopters of varying models, designated Marine One when the president is aboard any particular one in the fleet . Flights are typically handled with as many as five helicopters all flying together and frequently swapping positions as to disguise which helicopter the President is actually aboard to any would - be threats . </P> <P> For ground travel, the president uses the presidential state car, which is an armored limousine designed to look like a Cadillac sedan, but built on a truck chassis . The US Secret Service operates and maintains the fleet of several limousines . The president also has access to two armored motorcoaches, which are primarily used for touring trips . </P> <P> The U.S. Secret Service is charged with protecting the president and the first family . As part of their protection, presidents, first ladies, their children and other immediate family members, and other prominent persons and locations are assigned Secret Service codenames . The use of such names was originally for security purposes and dates to a time when sensitive electronic communications were not routinely encrypted; today, the names simply serve for purposes of brevity, clarity, and tradition . </P>

Where does the authority of the president come from