Review: Seiko Prospex “Marine Green” GMT
There’s been a gaping hole in the Seiko collection up until very recently: the GMT watch. Capable of reading multiple time zones at once, it was only in 2022 when that wrong was righted with the introduction of the affordable Seiko 5 GMT collection. But for those with a bit more to spend, who want a bit more spit and polish to their GMT watch, there’s now this, the first mechanical GMT in the Seiko Prospex collection. Could it be the GMT with the biggest bang for the buck?
Background
The need for a GMT watch came about with travel that went further, faster. Crossing the Atlantic in a ship took around three to four weeks, and the only method of communication was by letter, so there was little chance of breaching the age-old excuse for buying a GMT watch: waking up nana at home.
The expanding rail network in the US necessitated the use of four time zones, each an hour apart, established in 1883. This new railroad time was adhered to rigidly, where there had previously been hundreds of separate time zones that differed for every town. Still, with a variation of just a few hours, it wasn’t necessary to monitor multiple time zones at once.
It’s with the advent of jet propulsion that the GMT watch became a necessity. There are many reasons why a long-haul pilot would want to keep track of multiple time zones, least of all to avoid upsetting grandma. For a start, international aviation all operates on UTC, Coordinated Universal Time, to avoid the inevitable mix-ups of having multiple time zones and especially daylight savings. So it makes sense for a pilot to be able to monitor both the local time and UTC, which is essentially the same as GMT.
But why UTC and not GMT? And why UTC and not CUT, if the term is Coordinated Universal Time? Similar to railroad time, UTC was first introduced in 1960 to combat the safety risks of having fast-moving vehicles operating across multiple time zones. As it was an international endeavour predominantly between English and French-speaking countries, Greenwich Mean Time was discounted and two new names were proposed: CUT and TUC, short for “Temps universel coordonne”. As a compromise, UTC was chosen.
Transcontinental pilots also suffer from jet lag, and some choose to combat that by sticking to their home time. A GMT watch can be very helpful for maintaining a single time zone whilst also tracking local and UTC. World time pocket watches already existed, with the complication making its way to a wristwatch in 1940, but the overt complexity was too much and too expensive for modern pilots.
This was overcome in 1953, not by the Rolex GMT-Master as is often believed, but by the Glycine Airman, which established the 24-hour GMT form-factor we’ve since become used to. As is typical of Rolex, the GMT-Master came out a year later and overshadowed the watch that originally created the complication.
How does a GMT watch work? An extra hour hand, calibrated to a 24-hour rotation, is added to the watch. These days, either it or the 12-hour hand is independently adjustable, but the early watches relied on a turning bezel to set the second time zone instead. That’s how Rolex were able to release the GMT-Master so quickly in 1954, because the modification to the existing Turn-o-graph was very simple.
In theory, a GMT watch with an independently settable hour or GMT hand and a rotating GMT bezel is capable of tracking three time zones at once, but typically two is enough. For Seiko, this complication has long been underrepresented in the collection. In the 60s, Seiko had both a GMT and a world timer, but those watches were discontinued without a replacement. In 2021, there was the Spring Drive SNR033, but it wasn’t until 2022 when the GMT complication was added to the entry level Seiko 5 line. And now, in 2023, it’s been added in mechanical form to the Prospex collection for the first time ever.
Review
Seiko’s Prospex collection is a literal embodiment of the term “professional specifications”, and for the Prospex GMT, those specifications aren’t limited to just a GMT function. The first thing you’ll notice is that this GMT does not have a GMT bezel. The new calibre 6R54 has an independently settable GMT hand, but the ceramic bezel is that of a dive watch, segmented into minutes over the course of an hour.
This particular model, the SPB381J1 is the “Marine Green” variant. There’s a black “Dark Depths” version and a limited edition “Glacier Blue” version too. All are housed within a 42mm hardened stainless steel case, which although big, has short enough lugs not to wear too big, as you can see on my 7-inch, 18cm wrist. The watch appears to wear quite thick, although at 12.9mm it is less than a millimetre thicker than a Rolex GMT-Master II. The pronounced profile of the bezel is the likely culprit in this visual balance.
Overall, it is a very comfortable watch, with similar, if slightly reduced proportions to its more affordable sibling, the Seiko 5 GMT. But where the Seiko 5 GMT costs just £420, or around $520, the Prospex GMT’s price increases significantly to £1,400, or around $1,800. Why the big jump, and is it worth it?
Just a moment in the hand with the Prospex GMT will tell you why this watch costs more. The finishing of the watch sits somewhere at a happy medium between the Seiko 5 and the far more expensive Grand Seiko GMT offerings. Considering those start at some three times the price, that seems like a fair deal, and is a perfect example of the law of diminishing returns in full effect.
Does that make this watch the sweet spot in the range? Well, there are some downsides. Being part of the Prospex range means the inclusion of the Prospex “X” logo, which although some may find perfectly innocuous, has been known to make a watch feel cheaper. The clasp is lacking on-the-fly micro-adjust, although it at least has a three-fold clasp with extender.
Then there’s the calibre 6R54, based on the architecture of the non-GMT 6R35. It’s been known to be a reliable movement, but the timekeeping is rated at a pretty colossal -15/+25 seconds per day, which is way off for a modern watch. In practice, most will likely perform a lot better than this, but it’s a shame that Seiko can’t commit to a higher level of precision.
Otherwise, the watch really is brimming with professional specification. There’s 200m of water resistance from the screw-down crown, a three-day power reserve, the ceramic bezel with luminous pip at twelve and of course the GMT function. This is known as a “caller” GMT, where the GMT hand is settable, as opposed to a “flyer” GMT, where the hour hand is settable. There are merits for both, with the caller GMT being easier to set for calls abroad and the flyer for travelling.
What’s most impressive is the finish, which really does feel more Grand Seiko than Seiko. The case is polished and brushed in a very multi-faceted way, with small details like the crown edge and bezel lip given close attention. The date, although perhaps awkwardly placed, blends in with the sunburst dial. The hands and markers, including the second hand whose red dot and lume tip harks back to the 1968 Seiko dive watch, are crisp and bright.
At the price point, it sits at an interesting place between more functional dive watches like the Halios Seaforth and the sports-lux entries of Tudor, and with the added functionality of the GMT complication. It’s unusual in the combination of dive watch packaging with the GMT on top, with perhaps the closest alternatives being the less-polished Mido Ocean Star GMT at £1,110 and the glitzy Christopher Ward C65 Aquitaine GMT at £1,350.
Is the Seiko Prospex GMT the watch for you? It certainly offers a very compelling argument, packing in a lot of features and quality for the price, as Seiko is known for doing. The manufacturer gets the benefit of producing at scale, a rare advantage that often places it at the top of the pile for bang for the buck. With the GMT function too it gets a stand-out feature for an extra £240 over the base diver which, if you want to think about it this way, is far cheaper than buying two watches.
What do you think of the Seiko Prospex GMT? One to consider or a niche too far?
