In 1971 Boeing introduced the Boeing 747 Special Performance, SP for short. The airliner had an increased range and was a lot smaller than the 747-100, to compete with tri-jets such as the DC-10 and the Lockheed TriStar.
The 747SP was created, at the request of Pan Am, by shortening a Boeing 747-100. The new airliner could operate the then longest route in de world, from New York to Tehran, with Pan Am and Iran Air.
Although production ended in 1989 and only 45 aircraft were ever built, there still are a couple of 747SP’s in the skies today. Most SP’s that are still flying are used as private or government aircraft, some are used as enigine testbeds and NASA even uses one as a flying telescope, called SOFIA.