New Grand Seiko Spring Drive Ushio Diver 300 Watches

I might even cry. Grand Seiko finally did it.

A new pair of dive watches with the Spring Drive movement has emerged - the Grand Seiko Spring Drive U.F.A. Ushio Diver 300 SLGB023 and SLGB025, with a diameter of just 40.8mm. And that’s just the tip of the iceberg.

With U.F.A. Spring Drive technology, Grand Seiko can create the most precise spring-driven watches in any category. Dive watches remain somewhat romantic in the era of dive computers, so true divers must have high, strictly regulated accuracy to justify their status as instruments.

Why This Really Matters

In 2025, a pair of 37mm Grand Seiko "Ice Forest" watches were introduced at Watches and Wonders.

When the U.F.A. Spring Drive movement debuted at the last Watches and Wonders, the headline-grabbing feature was its accuracy of ±20 seconds per year, which is six times more precise than the already highly accurate 5-day caliber 9RA2 with a precision of half a second a day or 15 seconds a month. But honestly, this is nitpicking.

U.F.A. made what was already very precise and unique even more precise. While everyone focused on increased accuracy and the new micro-adjustable clasp, I noticed a more subtle but important detail. The new 9RB2 U.F.A. Spring Drive movement is housed in watches with a diameter of just 37mm, opening the door for smaller case sizes in other collections of the brand - and immediately Grand Seiko dive watches came to mind.

For comparison, the average diameter of Grand Seiko dive watches was about 44mm. With the new U.F.A. movement, it was clear that the brand had every chance to create a smaller diver. But would they go this route?

Case

The answer is yes, and these are the new Grand Seiko Spring Drive U.F.A. Ushio Diver 300 models - SLGB023 and SLGB025. The Evolution 9 case with the 9RB1 movement now has a diameter of only 40.8mm and a thickness of 12.9mm. This is a breakthrough compared to the blue Ushio SLGA023 with a 5-day power reserve, which had a diameter of 43.8mm and a thickness of 13.8mm.

With the new dimensions, Grand Seiko finally offers dive watches that match the strongest competitors in the popular dive segment. This is an important step for both buyers and the brand. Despite the reduced case size, all the strength and elegance we expect from Grand Seiko are preserved.

Both models have water resistance up to 300 meters, are equipped with a screw-down crown, and are made of high-strength titanium - which is 30% lighter than steel yet stronger. The Evolution 9 geometry is multifaceted, and the case is impeccably finished in the Zaratsu technique with alternating matte and mirror-polished surfaces that turn black under direct light. In my opinion, no other diver case in the world can compare to the finish of these models.

Each dial is surrounded by a ceramic bezel matching the case color, with a 60-minute scale featuring 120 clicks for precise adjustment and a knurled surface for a comfortable grip. The bezel feels pleasant in the hand.

Dial

Ushio is one of the brand's many beloved dial patterns and compositions. In Japanese, this means "tide" - a perfect motif for dive watches. The source of inspiration is the Japanese archipelago, which inspires not only Grand Seiko but Japanese culture as a whole.

Although the pattern is formed by pressing during the dial's production stage, its base is a hand-carved form by a Grand Seiko master. This gives each dial a unique "handmade" essence, making the wavy reliefs resemble the surface of calm water - like a photorealistic picture of tides. This is a testament to the brand's renowned mastery in creating dials.

The blue dial of the SLGB023 reflects the vast expanses of the sea with a gradient that mimics the light penetrating the ocean's depths, while the green SLGB025 is inspired by the serene beauty of shallow waters near the shore. Both feature gradients, but the blue is more restrained and deep, while the green is bright, almost faded in the center, and gradually transitions into black.

It might seem that such an impressive background would impair readability, but for Grand Seiko, beauty and readability are not mutually exclusive concepts. They are implemented at the highest level.

A full set of applied hour markers with diamond-cut edges gives them sparkle and beauty, while their large sizes provide abundant Lumibrite coating for excellent readability in any conditions. The hour and minute hands are wide, executed in the Evolution 9 style, and also filled with Lumibrite. The minute scale is located on a beveled relief rim (rehaute), allowing the beauty and texture of the dial to remain unobstructed, thus enhancing readability. A winning balance.

The only point I don't particularly like, but understand the necessity of, is the luminous counterweight of the second hand. In light, it rotates, showing the passage of seconds, but in darkness, the luminous circle does not indicate the current second - quite the opposite. However, due to the torque requirements of the Spring Drive, the counterweight must be positioned at the base of the hand, not at the end. Its function is to show that the watch is running, even if you are deep underwater in darkness.

Movement

As mentioned, these watches feature the U.F.A. Spring Drive 9RB1 movement, not the 9RB2 from the 37mm "Ice Forest." The only difference is the power reserve indicator has been moved to the front of the dial. For those doubting this decision, it's worth considering that with a solid case back and screw-down case, the indicator on the backside would be invisible. For dive watches, I believe a solid case back and reduced case thickness are more important.

The 9RB1 caliber, like the 9RB2, is automatic with a 72-hour power reserve and an accuracy of ±20 seconds per year (3 seconds per month). For comparison, the COSC chronometer requires accuracy of +6/-4 seconds per day. This movement operates within this parameter, but over a month rather than a day - impressive.

Bracelet

The SLGB023 and SLGB025 models come with Evolution 9 bracelets matching the case tone. This is a five-link bracelet with alternating width links, fully matte on the front. It appears more tapered than the larger Evolution 9 models, which many will appreciate. The clasp is equipped with a micro-adjustment introduced last year, but now it has been expanded and improved.

The bracelets feature a new clasp with a lock and micro-adjustment, allowing for fine-tuning up to 6mm. Additionally, an extension of up to 18mm is provided for wearing over a wetsuit, providing a total of 24mm of adjustment. The "GS" emblem on the clasp serves as a lock, preventing accidental opening - when shifted down, a red unlock indicator appears.

Conclusion

Given all of the above, it's clear why I and many others are so excited about this new pair of dive watches. Grand Seiko has always excelled in watchmaking - Zaratsu finished cases, high-precision Spring Drive movements - but the main barrier in the dive category was the large case sizes.

I don't argue that there is a market for larger Grand Seiko divers, but the 51.5mm lug-to-lug length of the SLGA023 may be too large for most wrists. Among popular Swiss divers, almost all iconic models are around 41mm. At 44mm, Grand Seiko divers could not compete on equal terms - until now.

With the SLGB023 and SLGB025 models measuring 40.8mm, Grand Seiko finally offers all its strengths - impeccably finished cases, nature-inspired dials, and unparalleled precision movement - in a size that has long been awaited.

No more "star" limitation, where all the advantages of Grand Seiko could be dismissed due to too large a case. The only thing that can be criticized is the luminous counterweight of the second hand, and even that is a minor point. There's nothing else to fault.

Although I didn't always like the style of the Evolution 9 hands, in sports divers, they look logical. And the proposition is clear: for 17,700 Australian dollars, you get the most accurate spring-driven dive watch in the world with 300 meters of water resistance, a titanium case, a stunning dial, 3 seconds per month accuracy, and improved micro-adjustment. All boxes checked.

For those who found the SLGA023 too large but loved the blue color, the marine SLGB023 is suitable. And for those who want a more original Ushio shade, there's the green SLGB025.

Grand Seiko Spring Drive U.F.A. Ushio Diver 300 SLGB023 and SLGB025: Price and Availability

The SLGB023 and SLGB025 models will be available for sale in June 2026. Price: $12,400 USD, 17,700 Australian dollars.