In order to prevent pilots and flight staff from suffering from jet lag on board of its Boeing jet, Pan-Am exposes the need to know simultaneously the local time of arrival and that of the place of departure.
That is how in 1954 the GMT-Master model appears on the market ("GMT" stands for Greenwich Mean Time now known as Coordinated Universal Time) which allows the display of the second time zone with the added ball that, making one complete rotation in 24 hours, indicates the time on specific graduated bezel from 0 to 24. The first model has a crate in three bodies of Oyster type guaranteed for water resistance of 50m, lacquered black dial, luminous tritium indices, continuous parts, Mercedes game balls with additional hand with a small bright triangle. The rotatable graduated bezel is made of bakelite and presents the indices of the 24 hours engraved on the bottom and filled with luminous material. On the same side there is also the color: red for the daytime and blue for nighttime. The bezel Bakelite, although of great aesthetic impact, will be replaced with a more resistant aluminum insert.
In 1964 it is introduced a new caliber, which in 1971 will also have the downtime; the shape of the shoulder-charging becomes more rounded and the knurled bezel becomes less marked. Also the dial has open parts, following the style of the previous underline quadrant. Under the index of the number 6 the written SWISS becomes SWISS T <25. Other changes take place in 1967 when the graphics of the dial features white lettering on matte black background and when new specimens have a 24h sphere marked by a larger triangle more readable (in the previous version the triangle, said "freccino", is smaller and brighter).
The new collection features new 5-digit Rolex references: 16750 (steel), 16753 (steel / gold), 16758 (gold) and 16760 (steel). The model Rolex GMT-Master 16750 in the mid-eighties renews the dial that acquires lucidity and "shorts" indices, but retains the glass in plexiglass.
The last specimens have the ceramic bezel with the inscription of the name of the model and the 24h ball in green.