In the 1950?s innovations in aviation technology made transatlantic travel a more appealing option than ever before. Due to the unprecedented success that the Rolex Sports models met with, it came as no surprise when Pan-Am, the world's largest airline, commissioned a watch to be designed to their specifications, enabling their pilots to keep track of time in two locations. In conjunction with Pan-Am's Captain Frederick Libby (a decorated World War II veteran and one of the airline?s most respected navigators), Rene-Paul Jeanneret devised a watch with an additional hour hand that revolved once every 24 hours and a rotating 24-hour bezel: the GMT-Master was born.
Although the watch had been made to Pan-Am?s requirements, many other pilots came to depend on the watch; particularly military pilots who kept the rotating bezel at "12", thereby enabling the watch to give them both civilian and military (or 24 hour) time. Among the pilots who came to rely on the GMT Masters were those chosen by NASA to fly the North American X 15. Rolex perceived the GMT-Master almost solely as a pilots watch. While it had been the introduction of the Boeing 707 that had caused Pan Am to commission the GMT Master, now the people who flew on them as passengers became the main customers for the watch. With the introduction of jet travel, people regularly traveled between countries and between time zones. In 1954, the first GMT Master, ref. 6542, was launched. This model was very distinctive, with Mercedes hands and an extra hour hand that was clearly differentiated by the triangle at its tip. Instead of the usual metal bezel insert, a special transparent acrylic insert had 24-hour markings printed on its underside. This material was chosen to cut down reflectivity for better legibility. This reference was produced from 1954 to 1960, at which time the the new GMT-Master Ref. 1675 was launched.