The Rolex GMT was designed as an aviator watch:
The newly introduced fourth hand allowed the display of an additional
time, with the corresponding numbermarkings on the outer bezel. Pilots
used the second time to display the Greenwich
led to the name Rolex GMT Master. Altough Greenwich Mean Time (GMT) got
replaced 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, altough Pilots nowadays use it to set UTC.
The Rolex GMT Master was developed in cooperation
with Pan Am. As in the 1940s and 50s
flying distances got longer and the pilots travelled through multiple
time zones, Pan Am asked Rolex in the 1950s to develop a watch which
could tell different times simultaneously.
The first GMT
(Ref. 6542) was a regular Turn-O-Graph (Ref. 6202) with a
different bezel and a modified movement.