The Rolex GMT was designed as an aviator watch: The newly introduced fourth hand allowed the display of an additional time, with the corresponding number markings on the outer bezel. Pilots used the second time to display the Greenwich Mean Time (GMT), which led to the name Rolex GMT Master. Although Greenwich Mean Time (GMT) got replaced in 1972 in the Aviation Industry by Coordinated Universal Time (UTC), the term GMT is still known and kept as part of the name of the GMT Master, although Pilots nowadays use it to set UTC.
The Rolex GMT Master was developed in cooperation with Pan Am. Flying distances increased in the 1940s and 50s, and pilots traveled through multiple time zones. Pan Am asked Rolex in the 1950s to develop a watch that simultaneously tells different times.