Grand Seiko finally has a Spring Drive dive watch in a 40.8mm size
Zach BlassI could actually cry. Grand Seiko finally, finally did it. We have a new pair of Spring Drive Dive Watches, the new Grand Seiko Spring Drive U.F.A. Ushio Diver 300 SLGB023 and SLGB025, that are only 40.8mm in diameter. And that is just the tip of the iceberg.
With U.F.A. Spring Drive in its arsenal, Grand Seiko, in any category of watch, has the potential to create the most accurate mainspring-driven watch in the world. Dive watches are already a bit romantic in a world with dive computers, so a proper dive watch needs to have legitimate, highly-regulated accuracy to really put the tool in tool watch.
The context – why this really, really matters
When U.F.A. Spring Drive debuted last Watches and Wonders, there was a clear surface headline worthy of applause – a spring-driven movement that runs within a pledged accuracy of plus or minus 20 seconds per year, which amounts to an accuracy six times greater than the already highly accurate 5-Day 9RA2 that is accurate within half a second per day, or fifteen seconds per month. But, to be honest, we’re splitting hairs here.
U.F.A. made something that was already very accurate and unrivalled even more accurate. So while everyone was fixated on the increased accuracy and the new micro-adjust clasp, I was metabolising the quieter, more subtle headline. With the new 9RB2 U.F.A. Spring Drive movement being inside of watches just 37mm in diameter, the door was thrust wide open for smaller cases across other parts of the brand’s catalogue – and immediately Grand Seiko’s dive watches came to mind.
To put it in perspective, Grand Seiko divers, on average, clocked in at around 44mm in diameter. So, with the new U.F.A. movement, I knew Grand Seiko had a clear path to creating a tamer-sized dive watch. But would they walk down that path?
The case
Well, the answer is fortunately yes with the new Grand Seiko Spring Drive U.F.A. Ushio 300 Diver’s – the new SLGB023 and SLGB025. The Evolution 9 case, thanks to the 9RB1 movement inside, now measures just 40.8mm in diameter and 12.9mm thick. This is game-changing, compared to the blue ushio 5-day SLGA023 diver that measured 43.8mm in diameter and 13.8mm thick.
With this new size, Grand Seiko is finally offering a dive watch that, dimensionally speaking, is more in line with the strongest competitors within the highly popular dive watch segment. So, it’s a big deal for both Grand Seiko watch buyers and the brand. Though the case has been scaled down to proportions more in line with favoured dive watch dimensions, Grand Seiko has retained all of the robustness and elegance we expect from its creations.
Both watches are 300 metres water-resistant with a screw-down crown and encased in the brand’s high-intensity titanium – 30% lighter than stainless steel yet even tougher. The Evolution 9 geometry is highly faceted and impeccably zaratsu-finished, clearly emphasising the brand’s light and shadow grammar of design with alternating bright brushed surfaces and glistening distortion-free mirror-polished surfaces going black under direct light. This is just my unforced opinion; there is no dive watch case from any other brand in the world that is better finished than what you see on these two watches.
Framing each dial is a colour-matched ceramic bezel insert with a full 60-minute timing scale, and the bezel, with its 120 clicks, allows for precise adjustment, and its knurling makes it easy to grip. It feels great in-hand.
The dial
Ushio is just one of the many beloved dial patterns and layouts the brand offers. It means tide in Japanese – a perfect pattern for a dive watch. The inspiration for the pattern comes from the Japanese archipelago – a source of inspiration for not just Grand Seiko, but also in broader Japanese culture and art.
Though ultimately pressed into the dial during the dial manufacturing process, the pattern is first born by one of Grand Seiko’s exceptional craftsmen, who hand-carves a mould that becomes the basis of what we see on the final dial. This means that each dial, though identical, has a handmade essence. It is also what makes the dial feel so natural, the wavy ridges of the dial perfectly mimicking the surface of serene water. It is almost like a photorealistic painting of the tides. A mark of Grand Seiko’s well-acknowledged mastery of dial crafting.
The SLGB023’s blue dial is said to reflect the vast expanse of the sea through a gradient that captures light streaming into the deep ocean, while the SLGB025’s green dial draws from the tranquil beauty of shallow coastal waters near the shore. Though both have a gradient effect, the blue feels less dramatic, yet it is so rich and swallows you in. The green dial has what I would describe as a clearer gradient, bright, almost washed at the centre, and gradually fading to black.
It may seem counterintuitive to have such a captivating backdrop that has the potential to hinder legibility of the indications. But, for Grand Seiko, beauty and legibility never come at the expense of one or the other. It’s both executed at the utmost, or not at all.
The full set of applied hour indices is precisely diamond cut, giving each the beauty and brilliance Grand Seiko demands of its components, and their large shape affords ample Lumibrite for unquestionable legibility in any lighting condition. You also have a broad Evolution 9-style hours hand and a broad arrow-tipped minutes hand – each sizably filled with Lumibrite as well. The outer minutes track is housed within the sloped rehaut, ensuring that the lines do not have to compete with the beauty and texture of the dial. This allows the dial pattern to have minimal interruption while also allowing the minutes track to have a backdrop that affords better legibility. A win-win.
Perhaps the one thing I do not particularly love, but I understand why it is done, is the lumed counterweight of the second hand. With the Lumibrite filling the counterweight, in darkness, the circle you see revolving around the dial will not indicate the current second – in fact, it is the opposite. But, with the torque requirements for Spring Drive, that element could not be housed on the tip of the hand rather than the base. So, what is the purpose of the lumed counterweight then? Ultimately, it is to signal that the watch is still running. So if you are hundreds of metres deep in the dark depths of the ocean, you can be aware of whether or not the watch is still keeping time.
The movement
As I mentioned earlier, these watches are driven by the U.F.A. Spring Drive 9RB1 – not the 9RB2 found in the 37mm ‘Ice Forest’ watches. The only difference is that the power reserve indicator has been moved to the front, on the dial side. For those who question having the power reserve indicator dial side, were it still on the movement, you would not be able to see it, as the watches have solid screw casebacks. And for a dive watch design, I am happy to have a solid caseback and the millimetre or so it can save in total case thickness.
The 9RB1, like the 9RB2, is an in-house automatic 3-day calibre and is accurate within 20 seconds per year or 3 seconds per month. A COSC chronometer requires +6/-4 seconds per day accuracy. This movement runs well within that parameter, yet per month, not per day, per month. Incredible.
The bracelet
The SLGB023 and SLGB025 are both outfitted with case-matching Evolution 9 style bracelets. So, we once again see a five-link layout with link pieces alternating in width and fully brushed on the front side. But, at least to the eye, it feels like there is a stronger taper than what you would find on larger Evolution 9 bracelets – which I think most of you watching this will appreciate. Once you reach the clasp, you will notice that these watches benefit from the micro-adjust system introduced last year. But it is actually an expansion and evolution of the clasp.
These bracelets include a newly developed locking extension clasp with the micro-adjustment introduced last year. In addition to a three-step micro-adjustment that allows for up to 6mm of fine-tuning, the extension feature, designed to be used with a diving suit, enables an additional 18mm, providing a total of 24mm of adjustment. The ‘GS’ emblem on the clasp functions as the locking mechanism, preventing the accidental release of the clasp – a red indicator when the emblem is slid down indicating it is unlocked.
The verdict
So, with all of this in mind, I think you can understand why I, and likely many of you watching this, are very, very excited about this new duo of divers. Grand Seiko has always had a strong point of distinction in its watchmaking – zaratsu-finished cases, highly accurate Spring Drive calibres, to name a key pair. But the potential roadblock, particularly, in its divers’ category has been its, until now, exclusivity in larger case sizes.
I am not saying there isn’t a market for Grand Seiko’s larger dive watches, but the SLGA023’s lug-to-lug of 51.5mm can be, even with the contour of the case shape, a bit intimidating for the average wrist size. When we look at popular Swiss dive watches, pretty much all of the dive watch icons have core variants sized closer to 41mm. So with an average of 44mm, Grand Seiko dive watches have never been able to be compared more apples to apples to their competitors – at least until now.
With the SLGB023 and 025, and its 40.8mm size, Grand Seiko has finally brought all of the alluring key distinctions it offers, impeccably well-finished cases, a beautiful nature-inspired dial, and a calibre with unparalleled accuracy, to the sweet spot a sizeable audience has been begging the brand to do for years and years.
There is no longer that looming asterisk where all of the distinct Grand Seiko elements are potentially disqualified in a watch buyer’s mind because they couldn’t get behind a 44mm or so watch. Literally the worst thing I can say about this watch is the lumed counterweight element. That’s it, and it is so, so minor. I cannot really pick apart anything else.
While I may not have always been enamoured with the broader Evolution 9 handset style at times, within the context of a full-on sporty dive watch, it makes absolute sense. The proposition is clear. For A$17,700 you can get the most accurate mainspring-driven dive watch in the world, 300 metres water-resistant, titanium, stunning dial, 3 seconds per month accuracy, enhanced micro-adjustment. It ticks all the boxes.
Those who felt the SLGA023 was too big, but loved the blue, have the sea-inspired SLGB023. And for those looking for an even more novel ushio flavour, the green shore-inspired SLB025 is another great option.
Grand Seiko Spring Drive U.F.A. Ushio Diver 300 SLGB023 & SLGB025 pricing and availability
The Grand Seiko U.F.A. Spring Drive Ushio 300 Divers, the SLGB023 and SLGB025, will both be available beginning in June 2026. Price: US$12,400, A$17,700
| Brand | Grand Seiko |
| Model | U.F.A. Spring Drive Ushio 300 Diver |
| Reference | SLGB023 SLGB025 |
| Case Dimensions | 40.8mm (D) x 12.9mm (T) |
| Case Material | High-intensity titanium |
| Water Resistance | 300 metres, screw-down crown |
| Crystal(s) | Sapphire front |
| Dial | SLGB023: Gradient blue, Ushio-patterned SLGB025: Gradient green, Ushio-patterned |
| Strap | High-intensity titanium bracelet, locking extension micro-adjust clasp |
| Movement | 9RB1, in-house, automatic, Spring Drive |
| Power Reserve | 72 hours |
| Functions | Hours, minutes, seconds, power reserve indicator |
| Availability | June 2026 |
| Price | US$12,400 A$17,700 |