In March of last year, Seiko unveiled the first mechanical GMT watches in its Prospex collection. The SPB381, SPB383, and SPB385 were “Mini Marinemasters” in green, black, and ice blue. Seiko calls this model the 1968 Diver’s Re-interpretation. Before, it was available as a dive watch only, but since last year, it’s also available with a GMT function. Now the Japanese watchmaker is introducing the Seiko Prospex SPB439. This new limited edition of 1,500 pieces features a textured white dial and supports its Save the Ocean marine conservation program.

This watch is no surprise to us all here at Fratello. As Lex already said, 2024 will be the year of GMT watches, and Seiko is here for it. The brand has already introduced quite a few other GMT models after kicking off with those first three references last year, and it sure looks like that will continue in 2024. And why not? The GMT complication is one of the most popular ones out there at the moment. Furthermore, the Mini Marinemaster is quite popular with fans who love the style of the legendary Marinemaster 300 —  the winner of our 2023 Seiko World Cup — but prefer more modest proportions. But enough with the background already; let’s take a look at the new Seiko Prospex SPB439.

Seiko Prospex SPB439

The Japanese Antarctic Research Expedition

All right, sorry; I suppose I should also give a little more background on the inspiration for this watch. As you know, its release is part of Seiko’s Save the Ocean initiative, which supports organizations dedicated to marine research and conservation. One of these is the National Institute of Polar Research (NIPR) of Japan. Back in the 1960s, Seiko’s diver’s watches and timing equipment were chosen for the NIPR-supported Japanese Antarctic Research Expedition. In 2021, Seiko once again lent its support by donating solar-powered diver’s watches (ref. SNE573) to the members of the 63rd Japanese Antarctic Research Expedition.

Seiko Prospex SPB439

The Seiko Prospex SPB439 Save the Ocean LE

The new Seiko SPB439, with its textured white dial, pays tribute to these Antarctic research expeditions. It has the same 42mm stainless steel case as the previous GMT and non-GMT versions of the 1968 Diver’s Re-interpretation. It’s also still 12.9mm thick and measures 48.6mm from lug to lug. Those dimensions make it a little more wearable than the original Marinemaster 300, which is 44mm in diameter and 15mm thick. Despite the smaller size, I still think the Mini Marinemaster has kept a lot of that bold and strong character that the original MM300 has.

The bezel contains a glossy black ceramic insert with the classic 60-minute diver’s scale on it. It surrounds the sapphire crystal, which is coated on the inside to inhibit reflections and allow you to take a good look at that textured white dial. On the rehaut, you’ll find the two-tone 24-hour scale with blue-green numbers on the lower half. They match nicely with the corresponding 24-hour hand and the GMT text on the dial. The Seiko and Prospex logos are printed at 12 o’clock, while the power reserve and water resistance specs are at 6 o’clock. As we’re used to with Seiko, the large indices and brushed hands contain a decent amount of LumiBrite, so it’s easy to read the time in the dark. Finally, there’s a date indicator between 4 and 5 o’clock, which doesn’t look too distracting against the white dial.

Capable of polar expeditions

The screw-down crown, which is located at 4 o’clock, allows you to control the 6R54 automatic caller-style GMT movement inside. It holds a power reserve of 72 hours, features 24 jewels, and runs at a 21,600vph frequency. It’s also resistant to magnetic fields of up to 4,800 A/m (about 60 gauss) meeting the ISO 764 standard. And, as this is a dive watch first, its case is water resistant down to a depth of 200 meters.

The stainless steel Oyster-style bracelet is one we already know from previous Prospex watches. It’s built well and starts at a 20mm width in between the lugs and ends at 18mm at the clasp. It also features a dive extension, so you can wear it over your dive suit on your next adventure.

Final words

In the end, I think the green SPB381 is still my favorite of the bunch, but this silvery-white textured dial is certainly a nice addition. The good thing, in my eyes, is that the texture isn’t that pronounced, so sometimes you see it very clearly, and other times you don’t. This gives the watch a different look every time you glance at it.

The Seiko Prospex SPB439 is available now for €1,800 and is limited to 1,500 pieces. For more information on its availability and specs, please take a look at the official Seiko website.

Let me know in the comments below what you think of this new Save the Ocean GMT.

Watch specifications

Prospex 1968 Diver’s Modern Re-interpretation GMT Save the Ocean
Textured silvery-white with applied indices and white/gray 24-hour rehaut
Case Material
Stainless steel
Case Dimensions
42mm (diameter) × 48.6mm (lug-to-lug) × 12.9mm (thickness)
Case Back
Solid stainless steel, screw-in
Seiko 6R54 — automatic and hand winding, 21,600vph frequency, 72-hour power reserve
Water Resistance
200m (20ATM)
Stainless steel three-row bracelet (20mm width) with diver's extension
Hours, minutes, central seconds, caller GMT (independently adjustable 24-hour hand), date, 60-minute diver's bezel
Special Note(s)
Limited edition of 1,500 pieces