In partnership with Seiko Prospex

Deep Dive: The Evolution of Seiko’s Professional Marinemaster Range

Seiko has a long history of making superior dive watches perfect for pros, weekend enthusiasts, and everyone in between. In this three part series, we’ll take a look at the histories of three distinct dive watch families under the Seiko umbrella – timepieces so iconic and treasured by watch aficionados that many have their own, unofficial nicknames – and track their evolution to today’s most modern, tech forward, Prospex iterations. 

Previously, we looked at the Turtle family of divers, a highly functional watch made for everyday use, ideal both for recreational divers and watch lovers needing a solid and durable timepiece. Today, we look at the Marinemaster range, and Seiko’s history of superior dive watches designed for professionals who risk their lives in the deep sea everyday.

The 1960s were something of a golden age for functional watches. Long before watches became collectibles prized for their rarity, they were purpose-driven instruments meant to do a specific job. In the ’60s, a new job that required specialized tools and brave workers was professional diving. The planet’s oceans, holding huge reserves of untapped natural resources, became fertile ground for exploration in the years following World War II, with technology finally able to (somewhat) safely keep divers submerged for ever increasing periods of time. For these professional divers, a reliable timekeeping instrument was essential, since a poorly timed decompression stop could easily lead to the Bends, or worse. The constant monitoring of dive time is an obvious necessity for staying alive underwater, and Seiko has been serving divers from the very beginning with a distinct series of timepieces designed for the most serious professionals, consistently focused on incorporating the most innovative design and advanced horological technology.

Seiko 6215-7000.

In 1967, Seiko introduced its first professional dive watch, the 6215-7000. While Seiko had built watches meant for diving before, the 6215-7000 was something altogether different. This watch was not intended for the casual, recreational dive enthusiast, but for divers who made their living with dangerous dives. While early Seiko dive watches had a water resistance rating of 150 meters, the 6215-7000 was capable of withstanding depths to 300 meters. It achieved this (at-the-time eye-popping) water resistance in part through its unique monocoque, or one-piece, case construction, keeping possible points of water ingress to a minimum. The 6215-7000 was also the first Seiko dive watch to feature a crown at 4 o’clock, a signature of Seiko divers to this day, and provides an obvious aesthetic link between these early professional diver watches and the highly advanced Prospex divers of today.

Seiko 6159-7001, notable for its high frequency movement running at 36,000 bph.
The 6159-7001’s monocoque, or one-piece, case design.

One of the most highly sought after Seiko dive watches in the collectible market, the 6215-7000 was only produced for a year before being replaced by the 6159-7001. This new version was nearly identical in appearance and construction to the 6215-7000, but featured a high-frequency movement operating at 36,000 bph. High-beat movements have come to be something of a specialty for Seiko, offering greater precision and rate stability over time compared to movements that run at more traditional frequencies. Naturally, they are more difficult to produce and to tune correctly than a standard movement, but over the decades, Seiko has become a leader in manufacturing and properly regulating high-frequency movements. The 1968 introduction of the 6159-7001 was a true milestone in watchmaking, and it’s regarded as the world’s first high-beat dive watch.

The 6215-7000 next to its successor, the 6159-7001.

These early professional dive watches laid the groundwork for what the public came to expect from Seiko’s  highest-end, premier divers. The SBDX001 Marinemaster 300 was the next logical step in the chain of Seiko’s pro divers, providing the clearest link to the modern watches in today’s Prospex line. While the SBDX001 was produced exclusively for the Japanese market, many were imported to the United States and elsewhere, offering an obvious value over far more expensive Swiss competitors. The construction, still monocoque, is superb, and by the time this watch showed up at the start of the 21st century, the basic physics behind the case design had been proven over the course of a generation, and was further refined as Seiko’s production capabilities and techniques grew and became more advanced. The SBDX001 was not only an essential tool for divers, but represented a peak in engineering  for Seiko obsessives all over the world.

The constant monitoring of dive time is an obvious necessity for staying alive underwater, and Seiko has been serving divers from the very beginning . . . consistently focused on incorporating the most innovative design and advanced horological technology.

Seiko SBDX001 Marinemaster 300.
Another monocoque design.

In appearance, the Marinemaster is similar in shape to the professional dive watches that came before it, but with production starting on the SBDX001 in 2000, the overall quality of the finishing is sharper than on the true vintage models. Viewing the case in profile or from an angle reveals subtle but well-executed transitions between polished and brushed surfaces, with remarkably thin bevels and graceful, flowing case lines. The movement powering the Marinemaster is the 8L35 caliber.

With a renewed interest in vintage watches, the Prospex line has taken the opportunity to build on the legacy of the Marinemaster, the 6159, and the 6215 with a series of ultramodern divers that take plenty of design cues from Seiko’s back catalog while offering up only the best in current watchmaking tech.

Seiko SLA025, the 1968 Automatic Diver’s Re-creation Limited Edition.

One of Seiko’s key strengths is recognizing when and how to reintroduce classic designs to the market. With the SLA025, a limited edition released in 2018 in a run of just 1,500 pieces, the brand paid tribute to the legendary 6159-7001.  The full name of the watch, the 1968 Automatic Diver’s Re-creation Limited Edition, gets to the heart of what the SLA025 is all about and what Seiko is capable of doing when it comes to digging through the archives. This timepiece is faithful to the original in all of the important details, from the distinctive hand set to the 4 o’clock crown to the classic case shape. The SLA025 is fitted with Seiko’s Hi-Beat 8L55 movement, a logical choice considering the lasting importance of the 6159-7001’s ability to bring a high frequency caliber to the depths of the world’s oceans. The SLA025 also won the coveted Sports Watch Prize at the 2018 Grand Prix d’Horlogerie de Genève.

Seiko SLA025 on the wrist.

If you missed out on the SLA025, or long for a great example of a vintage Seiko diver but can’t part with the five figure sums often required for the best pieces, the Prospex SPB077 is a must-have. Based heavily on the 6159 design, the SPB077 is an exceptional modern interpretation of the classic. While the dial details, 4 o’clock crown, and case lines all bring the 6159 clearly to mind, the SPB077 is a modern watch in vintage clothing – the bezel is noticeably glossy, offering a flair distinct from that of the more workmanlike vintage examples, and the case is constructed in a traditional three-piece design, accessible from the back, unlike the monocoque cases of the past. The end result is a slim, modern reimagining of a watch that is an important part of Seiko’s history, and while it has benefitted from the trappings of modern manufacturing techniques, it loses none of the charm of the original.

Seiko Prospex SPB077.

While the SPB077 is a tribute watch that holds its own in a professional diving setting, the SLA021 can be thought of as the modern, no-compromises heir to everything the Marinemaster represents. While the dial doesn’t say “Marinemaster,” the heritage here can’t be disputed. It’s a dead ringer for the SBDX001, but with modern Prospex features that set it apart. The bezel insert, traditionally made of scratchable aluminum, is now ceramic, while the case finishing makes use of Seiko’s best Zaratsu polishing techniques, providing a mirror-like sheen and a level of refinement uncommon on watches this technically advanced.

Seiko Prospex SLA021.

Since the advent of professional diving, Seiko has been at the forefront of creating the timekeeping tools that divers need to do their jobs safely.

At the top of Seiko’s range of professional divers sits the GPHG-award-winning Prospex LX SNR029. While, on the surface, this could easily be mistaken for the SLA021, it’s a different animal entirely. The power reserve on the dial gives away its not-at-all-little secret — it’s powered by a Spring Drive caliber. Spring Drive is perhaps Seiko’s most important watchmaking achievement since the advent of quartz. Combining a mechanical gear train with electronic time regulation, Spring Drive is more than simply a “best of both worlds” option; it’s a distinct step forward in watchmaking technology, and as used in a professional dive watch represents a new standard not just in timekeeping, but in safety. With an accuracy of +/- 1 second per day (+/- 15 seconds per month), the reliability and precision of Spring Drive technology should give any professional diver a sense of confidence as they descend to complete the dangerous work that they do.

Seiko Prospex LX SNR029.

The SNR029 is also distinct from other watches in this realm of the Prospex lineup in its case material. Milled from titanium, the SNR029 is significantly lighter on the wrist than its steel counterparts, making it a versatile and ergonomically superior choice. While the SNR029 isn’t a small watch by any means, the lightweight materials used make it wearable for almost anyone, whether deep under the ocean’s surface or topside. The natural gray hue of the titanium gives the watch an instrument-like look, but the finishing is still typically Seiko, which is to say, uncompromising. It’s truly impressive that the craftspeople behind Seiko’s case finishing are able to make this very industrial material appear beautiful.

Since the advent of professional diving, Seiko has been at the forefront of creating the timekeeping tools that divers need to do their jobs safely. From the early high-frequency divers of the ’60s, to the Marinemaster, to the modern line of Prospex professional divers, Seiko has left nothing on the technological table in order to bring their customers the most useful instruments to excel in their work.

To learn more about Seiko’s Prospex range, visit

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