With the beginning of jet transatlantic flights in 1956, Pan Am, the world's largest airline, wanted to find a way for their pilots to keep track of "home" time while in another time zone. A joint Pan Am and Rolex team devised a watch with an additional hour hand, which revolved once every 24 hours, and a rotating bezel marked with those same 24 hours. The model was named "GMT-Master" after the world's standard time, the Greenwich Mean Time.
The first GMT model, reference 6542, was launched in 1954 and was immediately recognizable by the bright acrylic or bakelite bezel insert. Reference 1675 came only five years later, and stayed in production until 1980, and reference 16750 followed, introducing the quickset feature.