The Rolex GMT-Master line is, of course, the brand's most famous GMT watch collection. However, it is not the only GMT model from the Swiss watchmaking giant; the other option is the Explorer II. Have you ever wondered whether or not the Rolex Explorer II is a GMT watch? Well, yes it is, and here's why.
To avoid confusion about A.M. and P.M. hours, daylight savings, and different time zones, pilots follow one standard time based on a 24-hour scale. The accepted standard aviation time was once called Greenwich Mean Time (aka GMT), which is the local time at Prime Meridian (0° Line of Longitude), which runs through Greenwich, England. The term GMT has since been replaced by Coordinated Universal Time (UTC). It is sometimes also referred to as Zulu Time because the letter "Z" (phonetically "Zulu") represents a "zero" offset (UTC +0).
As commercial airlines were flying faster and further distances in the 1950s, it became necessary for pilots to continuously track multiple time zones. Consequently, Pan Am Airlines asked Rolex to come up with a solution and the watchmaker officially presented the GMT-Master watch in 1955. The watch’s clever design allowed pilots to simultaneously read both reference time (GMT) and local time (depending on where they were landing), thanks to a fourth hand that pointed to a 24-hour bezel. Because the two-hour hands were synced, the bezel could be rotated to align the correct hour with the 24-hour hand to display GMT. Although simple in execution, the Rolex GMT-Master set the blueprint for the GMT watch genre.
The Rolex GMT-Master eventually graduated to become the GMT-Master II in the 1980s, where the two-hour hands of the Caliber 3085 movement could be set independently from one another. This now meant that the GMT-Master II could indicate three time zones at once: local time, reference time, and a third time zone by simply turning the bezel.
When Rolex introduced the Explorer II in 1971 as the ref. 1655, it too had an additional 24-hour hand and a 24-hour marked bezel. However, its bezel was fixed and the two-hour hands were synced. Therefore, it could not indicate another time zone. Instead, the Rolex Explorer II was a watch that offered a prominent day/night indicator, specifically intended for those who spent time in places like dark caves or polar regions, where looking to the sky for guidance was simply not possible.
However, Rolex eventually replaced the ref. 1655 with ref. 16550 in the mid-1980s, and by this time, Rolex had already developed the Caliber 3085. And since the Explorer II 16550 was fitted with the Caliber 3085, which featured decoupled hour hands, the watch now became another GMT watch option in Rolex's catalog.
From the mid-eighties onwards, the Rolex Explorer II line evolved from the 16550 to the 16570 to the 216570 and each of these references are indeed GMT watches, often referred to as dual time watches. The Mercedes-style hour hand serves to indicate local time while the arrow-tipped hand pointing to the 24-hour fixed bezel displays reference time (which can be GMT, home time, or any other time zone that the wearer chooses). There's also the date window, which shows the date in the current local time zone.
Additionally, the Rolex Explorer II offers what is now known as "true" GMT functionality because the local hour hand can jump ahead or behind in one-hour increments without disturbing the other hands. This is especially practical for frequent travelers who often find themselves in different time zones - changing the watch's time is just a matter of moving the 12-hour hand backward or forward in one-hour increments, depending on the direction of travel.