Archives & heritage

Zulu time


February 2018

Zulu time

Compared with Universal Time and its traditional 24 time zones, the GMT watch is more modest in its offerings: a second time zone, a second ‘point of reference’. Because, in the same way that standard time was born of the need to coordinate the railways, the GMT function is a direct result of the aviation boom of the 1950s.


n the 1950s the growing number of aeroplanes crossing time zones in all directions made the adoption of a single reference time – valid for every aircraft, in all locations, whatever the local time – a necessity. By adopting Greenwich Mean Time (GMT) as the time of reference for all aeroplanes, air traffic controllers and flight plans, it was finally possible to prevent the sort of confusion that could have dire consequences. It was the birth of the famous ‘Zulu time’.

One brand instantly understood the full potential of this decision: Rolex. In collaboration with the famous Pan Am company, in 1954 Rolex launched the GMT Master, reference 6524, which has become the ‘mother’ of all GMT watches.

The principle was simple, the design ergonomic, the function highly practical, and time setting was child’s play. And it was a runaway success.

A fourth luminescent hand, instantly recognisable with its arrow shape, travels around the dial in 24 hours, pointing to a rotating bezel with 24 graduations. It is independently adjusted by the crown in position 2. The arrow is set to indicate the time of departure – Zulu time for aviators, home time for their passengers – then, without interfering with the minutes and seconds, the 12-hour current time hand is set to the time zone you are currently crossing or that of your destination. Nearly every brand quickly followed suit. Breitling, which with its Breitling Navitimer had already collaborated actively with the world of aviation and was the official timekeeper for the Aircraft Owners and Pilots Association (AOPA), began releasing GMT models in the early 1960s. It introduced the Chrono-Matic, combining a dual time zone with GMT hand and a manually-wound chronograph.

Rolex GMT
Rolex GMT
The Rolex GMT-Master II needs no introduction. Pictured here in its most recent version, it features a Cerachrom rotating bezel, Parachrom balance spring, Oyster bracelet, Triplock winding crown and self-winding 3186 movement.

In 1969 it was Omega’s turn to launch its Flightmaster series, ‘for intercontinental travellers’. Using seven brightly-coloured contrasting hands, three crowns and two push-pieces, the wearer can activate a chronograph with interior rotating bezel and move a bright blue GMT hand in the shape of an aeroplane.

All this is housed in a large, oblong-shaped case. Production continued until the mid-’70s. Practically every watch brand released something similar and there are countless GMT watches, as well as those opting for a different configuration but with the same functions – known as ‘dual time zone’ watches. More ‘civilian’ and less ‘professional’, dual time zone watches allowed for all display types, therefore departing from the sporty aesthetic of the GMT. They were, in their way, the dressier version of the traveller’s watch – also ideal for non-travellers.


"You are taking the 11.30 p.m. flight from Paris to Tokyo (in the winter). Move the 12-hour hand forward by 8 hours. Your watch changes date and now displays 7.30 a.m. As for the GMT hand, it of course continues to display 11.30 p.m. on the bidirectional bezel. It has become your ‘home time’. If you are not travelling but are in regular contact with New York, for example, adjust the GMT hand so that it is displaying a time on the bidirectional bezel that is 6 hours behind Paris time. When your watch displays midday in Paris with the 12-hour hand, the GMT hand will point to 6 a.m. on the 24-hour bidirectional bezel. The second non-traveller option gives the same result: your two hour hands are set to the same time; 12-hour/24-hour synchronisation. Rotate your 24-hour bidirectional bezel in a clockwise direction by six notches (one notch per hour). Your watch will still show the same time on the 12-hour hand but the GMT hand will now be pointing to 6 a.m., the time in New York.

It is also possible to temporarily display a third time zone! Example: you are in Tokyo. The time difference is 8 hours ahead of Paris in the winter. It is 9 p.m. in the Japanese capital, so the 12 hour hand shows 9 o’clock on your watch dial and your GMT hand shows 1 p.m. (in Paris) on the 24-hour bidirectional bezel. All you need to do now is turn your bidirectional bezel in a clockwise direction by six notches to display the time in New York (which is 6 hours behind Paris). Your GMT hand will now show that it is 7 a.m. on the East Coast of the United States. The GMT hand can also serve as a compass, when the watch is parallel to the ground with the 12-hour hand pointing towards the sun. The GMT hand set to the same time according to the 24-hour GMT display then indicates north in the Northern Hemisphere."