Grand Seiko's U.F.A. Ushio 300 is its most
Grand Seiko has launched the Spring Drive U.F.A. Ushio 300 Diver, its most compact dive watch to date. The watch features a High-Intensity Titanium case, 300m water resistance, and a new ultra-accurate movement rated to ±20 seconds per year.
Grand Seiko has introduced the Spring Drive U.F.A. Ushio 300 Diver, which the brand states is its most compact diver's watch to date. The watch is engineered for diving performance and daily wear, featuring a case measuring 40.8mm in diameter and 12.9mm thick, crafted from High-Intensity Titanium.
According to the report from Hypebeast, the timepiece is built around the new Spring Drive Caliber 9RB1 movement. This movement has earned Grand Seiko's "Ultra Fine Accuracy" (U.F.A.) designation, delivering an annual accuracy of ±20 seconds, or roughly ±3 seconds per month.
Movement and Engineering
The Caliber 9RB1 is a 33-jewel self-winding movement assembled at the Shinshu Watch Studio. Its precision stems from a vacuum-sealed crystal oscillator and a low-power IC. Each oscillator undergoes a three-month aging process before frequency measurements across temperatures allow for precise thermo-compensation programming.
The sealed design minimizes external impacts from temperature, humidity, static electricity, and light. The movement measures 30.0mm in diameter and is 4.7mm thick, driving a 72-hour power reserve with a dial-side indicator. It also includes an integrated regulation switch for after-sales service to correct accuracy over time.
Case, Materials, and Specifications
The slim movement architecture enables the watch's compact proportions. The case and bracelet are made from High-Intensity Titanium, a material Grand Seiko says is about 30% lighter than stainless steel with high scratch resistance.
| Feature | Specification |
|---|---|
| Case Diameter | 40.8mm |
| Case Thickness | 12.9mm |
| Water Resistance | 300 meters |
| Magnetic Resistance | 4,800 A/m |
| Movement Accuracy | ±20 seconds per year (±3 seconds/month) |
| Power Reserve | 72 hours |
| Movement Diameter | 30.0mm |
| Movement Thickness | 4.7mm |
The watch includes a screw-down crown, a solid screw case back, and a rotating bezel with a ceramic insert for scratch and corrosion resistance. The lugs are designed with a broad profile to enhance light reflection and wrist presence.
Dial and Finishing Details
Legibility is a key focus, with Evolution 9 Style indices and Lumibrite-filled hands beneath a sapphire crystal with an inner anti-reflective coating. The dial features a textured "Ushio" (tide) pattern in a gradient design inspired by sea waters around Japan.
The dial is offered in two variations: a blue gradient representing deep ocean light and a green gradient inspired by shallow coastal waters. A newly developed locking extension clasp completes the watch. It provides a three-step micro-adjustment system with up to 6mm of fine-tuning and an 18mm diving suit extension for a total of 24mm adjustment. The GS emblem on the clasp acts as a locking mechanism.
The Spring Drive U.F.A. Ushio 300 Diver collection is available through Grand Seiko's official website and physical boutiques.
