The GMT Watch, Explained

The GMT watch is brilliant not because of its complexity but because of its simple ingenuity. Here's what you need to know about it.

rolex gmtii

If ever there were a hyped watch complication, it's the GMT in the 2020s. It's popularity is justified on several counts: complications make a watch more interesting, and the GMT is one of the most accessible steps above a watch with just basic time telling — at least, it's more affordable than the ever-popular chronograph. Moreover, the extra hand and common addition of the (often colorful) rotating bezel lend themselves to fun sporty designs. But most of all, a GMT is actually useful in modern life.

There's a lot to unpack in all those great reasons to want a GMT, and that's exactly what we do below. Here's what you need to know about GMT watches, where they come from, how they work and why they're cool.

Origin of the GMT Watch

pan am jet gmt ad
A vintage ad for the Rolex GMT-Master

On May 2, 1952, 36 people boarded a De Havilland Comet jet owned by the British Overseas Airways Corporation (BOAC) and flew nonstop from London to Johannesburg. The Jet Age had officially begun. Pan Am quickly ordered 20 of Boeing‘s new 707 jetliners and built its WorldPort terminal at JFK while TWA countered with its own World Flight Center. It was a brave new world that saw cigarettes on planes but not a roller bag to be found. People were suddenly able to fly across oceans and time zones in a day, which also introduced the decidedly modern ailment known as jet lag.

The pilots flying these long haul routes needed a way to keep track of time, both local time and the time in the place from where they departed. Introduced in 1953, the Glycine Airman was made to meet their needs with a watch displaying the time in 24-hour (rather than 12-hour) format, featuring a rotating bezel and 24-hour markings that could be used to track a second time zone. It's a cool and interesting solution (and the watch is still available today), but it wasn't the one that caught on.

Pan Am approached Rolex, the watch brand that Hillary wore up Everest and Cousteau wore in the deep, and requested a watch built for this new breed of pilots. In 1954, the GMT-Master, a watch that could mechanically track two time zones simultaneously, was born.

What does "GMT" stand for?

Though Rolex's approach was novel, the concept upon which it was based was not new in the 1950s. It dates back to 1884 when an international convention declared Greenwich, England as the “Mean Time” against which the rest of the Earth’s time zones would be compared. But GMT (Greenwich Mean Time) was established in an era of slow boat travel, when time zones were crossed over days and weeks, not hours. Jet airplanes changed all that.

rolex gmt master ii watch on the wrist of a man in a suit
The Rolex GMT-Master II is today a status piece even more than it is a practical travel watch.
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By 1955, the atomic clock had been invented, and in 1960 the US and UK synched their atomic radio time signals into what would become Universal Time Coordinated, or UTC, which effectively replaced that meridian line passing through the Royal Observatory in Greenwich. But the name “GMT” stuck and still somehow conjures up the dawn of the Jet Age, when knowing where you were in relation to a stripe on the ground in Old Blighty was first made important — just as the famous red-and-blue bezel of that first GMT-Master watch on the wrist of a Pan Am captain does.

How does a GMT watch actually work?

The GMT watch is brilliant, not because of its complexity but because of its simple ingenuity. As the movement's going train (primary series of gears) in a conventional watch is made to spin the hour hand around the dial every 12 hours, all that is required to become a GMT tracker is simply a second hour hand geared to run half as fast and an additional 24-hour time scale. The 24-hour hand circles the dial once a day instead of twice, its tip pointing to the corresponding hour, leaving no confusion as to whether it’s a.m. or p.m.

The iconic red-and-blue “Pepsi” bezel that is so associated with the Rolex GMT-Master was Rolex’s first solution to the two-timing conundrum. The so-called “GMT hand” points to the 24-hour time scale on that bezel (blue for nighttime hours, red for daylight). And because the bezel turns, any hour can be set to correspond to the GMT hand, thus instantly tracking a second time zone, just like Glycine's solution.

But if the bezel allowed for the tracking of any second time zone, why was the watch called the “GMT” Master? As part of their navigation and communication protocols, pilots always operate on GMT (or UTC) time, to eliminate any confusion. So those Pan Am pilots would always have their 24-hand set to GMT, no matter what their local time was.

vintage rolex gmt master gear patrol lead full
The look of Rolex’s red and blue "Pepsi" dial helped define the GMT genre.
Gear Patrol

If the Breitling Navitimer chronograph was the definitive pilot’s watch of the 1950s, its slide rule bezel and busy dial made it a quaint relic by the time the Jet Age hit its stride in the ’60s. The GMT-Master became the de facto pilot’s watch, and was seen on the wrists of fighter jocks and astronauts alike. But the Rolex, and other watches that followed suit, trickled down to coach class too, as jetset travelers saw the obvious advantage of a two-time zone watch, as well as the image it projected. Wearing it branded one as a traveler, someone who crossed time meridian lines and explored exotic corners of the world.

The earliest GMT watches were simple beasts: the 24-hour hand was anchored to the hour hand so that as you adjusted your local time, the GMT hand moved in tandem, thus tracking the local time as well, but on a 24-hour scale. To set a second time zone, it was thus necessary to turn the bezel. Later, it became possible to set the 24-hour hand independently.

What to look for in a GMT watch

Nowadays, there are more sophisticated movements than those early models, and they can be generally divided into two types. The first type has an independently adjustable GMT hand, meaning it can be set separately from the local time indicated with the hour hand and is not linked to the date function.

The second type links the GMT hand to the minute hand while the normal hour hand is independently adjustable and is linked to the date. The second kind is considered more of a classic GMT watch and is slightly easier for use while traveling, since flipping the hour hand forward or back without messing with the minute hand is quick and easy as your plane touches down in London or Buenos Aires.

While GMT watches were first created for pilots and are historically linked to aviation, they have since taken on a reputation as a consummate adventurer’s watch, useful for the one-watch traveler who wants to touch down in Kinshasa and head straight into the jungle. Good water resistance, rugged cases and legibility are the hallmarks of the new breed of GMT watches.

How to operate a GMT watch

As noted above, there are different kinds of GMT watches but there are often common principles to operating them. For many GMT watches (such as those using ETA or similar movements), the crown is pulled out to the same position as that which sets the date. One direction sets the date and the other advances the GMT hand. This is easy enough, and allows the user to set the second time zone without disturbing the current time.

10 best mechanical watches for travel gear patrol lead full
The 24-hour hand on GMT watches is usually arrow-shaped and brightly colored, making it easy to distinguish.

For something like the Rolex GMT-Master II, however, one position of the crown allows you to adjust only the main time's hour hand in either direction, whereas the GMT hand must be set along with the main time. There are yet more, fancier methods, but those mentioned here will serve you well in most cases.

These different methods have unofficial names. The first method above is sometimes called a "caller" (for those at home calling abroad) or "office" GMT, because it's easier to set the second time zone while the main time remains untouched. The latter is dubbed a "flyer," "travel" (or "traveller") or "true" GMT by collectors, though that shouldn't be understood to indicate that any one method is more legitimate than or superior to the other.

So, you've got your GMT watch set to two time zones via the above method. Want a third? If it's the kind of GMT with a rotating 24-hour bezel, just turn the bezel to align the current time in your desired locale to match up with the GMT hand. Presto. You've got yourself a deceptively simple watch elegantly displaying no fewer than three time zones. In a world increasingly connected by both travel and communication, there's still a strong case for a GMT watch's utility.

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