In 1968, Seiko unveiled the groundbreaking diver ref. 6159-7001, which was engineered to withstand the extreme conditions of diving. Its monocoque 300m water-resistant case housing a high-frequency 10-beat movement was way ahead of its time, and became symbolic of Seiko’s engineering capabilities. The historic model remains emblematic of Seiko Divers to this day and has spawned a lineage of modern-day iterations that continue to blaze the spirit of the 1968 Diver.

This year, Seiko unveiled the Seiko Prospex Marinemaster 1968 Heritage Diver’s Watch as a salute to the forward-looking endeavour of the 1968 Diver. Much of the original blueprint and proportions are maintained, as Seiko Design Leader Masanori Kawamura pointed out in our interview with him. “There are two aspects of the 1968 Diver 6159-7001 that I found particularly striking. One is the sloped, mirror-finished surface that wraps around the entire case, and the other is the crown at four o’clock.” Even though 58 years have passed since the 1968 Diver was unveiled, Kawamura still finds the geometry a timeless touch. “At a time when relatively simple shapes were common in manufacturing, this design was highly functional — achieving both a reduced sense of thickness and a well-balanced visual appearance. This surface composition controls how light is reflected and sharpens the overall silhouette of the case, which I feel is one of the reasons it does not appear dated, even when compared to contemporary designs.”

At first glance, this year’s iteration suggests a strong sense of familiarity with the original, but as Kawamura confirmed, it is a refinement of the Seiko Prospex Marinemaster SLA079. Subtle details such as the dial’s grained texture, bevelled indices, glossy ceramic bezel insert and the newly developed bracelet clasp are all nuggets of interest waiting to be discovered. To get a better understanding of the watch, Masanori Kawamura talked us through the watch’s design and his thought process behind the design choices.

Since we are on the subject of dive watches, what is your favourite coastal region to visit in Japan?
I don’t usually go diving, but I enjoy sailing on a cruiser from time to time, especially off the coast of Zushi, just south of Tokyo. It’s known for its scenic coastline and popular sailing waters.

Apart from watches, what are some of your interests or hobbies that enrich your design vocabulary?
I’m not sure whether this serves directly as a source for design ideas, but I have always loved looking out for and collecting interesting gears. I can be spending the weekend with my family, but if I chance upon any, I’ll just load them into the car, and then carry on with our weekend.

I have also been sailing on cruisers and participating in regattas for over 10 years, though it’s less frequent now because I’m committed to my family and children. Through these experiences, I feel that my awareness of usability, reliability, and simple function-driven forms in tools used in natural environments has, in the end, influenced my own design.

When you first began working on the new Marinemaster HBF001, what materials from the Seiko archives did you study most closely?
The HBF001 is positioned as an updated model of the SLA079, so rather than referring to specific archival materials, we proceeded with development based on the design and philosophy already established with the SLA079. For that reason, rather than focusing solely on re-examining past models in detail, we focused on identifying which aspects should be evolved, building on an already high level of completion.

What were the two most interesting details of the original 1968 6159-7001 diver that you discovered during your research?
There are two aspects of the 1968 Diver 6159-7001 that I found particularly striking. One is the sloped, mirror-finished surface that wraps around the entire case. This is not merely a finishing detail but a functional form designed to minimise distortion while ensuring visual continuity of the surfaces, and it strongly reflects Seiko’s design philosophy. The other is the crown at four o’clock. Its placement accounts for operability when worn, and minimises interference with the wrist, demonstrating a thorough pursuit of usability as a diver’s watch.

What design aspects of the original 1968 6159-7001 diver still feel modern to you today?
What still feels modern to me today about the 1968 Diver 6159-7001 is the sloped geometry applied across the entire case. At a time when relatively simple shapes were common in manufacturing, this design was highly functional — achieving both a reduced sense of thickness and a well-balanced visual appearance. This surface composition controls how light is reflected and sharpens the overall silhouette of the case, which I feel is one of the reasons it does not appear dated, even when compared to contemporary designs.

When redesigning a watch with such a strong and distinct history, how do you decide which elements must remain untouched and which can be changed?
Based on the history and achievements accumulated over time, we have organised discussions within the Prospex team to clarify which elements constitute the essential design codes. On that basis, we place importance on maintaining elements that are directly tied to function and practicality, as well as those that symbolise the model.

At the same time, we actively review areas where improvements in function or updates in expression can be achieved, in response to changes in materials, manufacturing techniques, and usage environments. In this way, we are able to carefully balance what should be preserved and what should be evolved.

Was there a design feature that you wanted to modernise more aggressively, but ultimately decided to keep closer to the original watch?
This model has been developed to embody a “dignified presence” that conveys its history and achievements. When it came to the Arabic numerals on the bezel, we did consider refining them into a more modern expression. However, in the end, we prioritised preserving the strength and presence of the original design.

As a result, compared to the SLA079, the numerals are slightly wider and more closely aligned with the original. At the same time, the overall stance and proportions have been adjusted in a more contemporary direction — achieving a balance between innovation and heritage.

The ceramic bezel, new clasp, and improved finishing all make the watch feel more contemporary. How did you ensure these additions enhanced the design rather than overpowering its heritage?
We design our models on the premise of preserving the 1968 Diver’s design codes, so that even with updated materials and finishes, the identity remains instantly recognisable.

At the same time, modern elements such as the ceramic bezel, new clasp, and updated finishes are carefully adjusted so that they do not stand out excessively on their own but instead integrate naturally into the overall proportions and balance. As a designer, rather than simply reproducing heritage, I aim to present it as something that has naturally evolved through contemporary technology.

What do you hope people will feel when they strap on the new Marinemaster HBF001?
I hope that the moment it is worn on the wrist, one can immediately feel the solid construction and reliability of a professional tool. At the same time, I would like the wearer to experience a sense of carrying the history and achievements of the 1968 Diver. Beyond pure functionality, I would be delighted if this model could also convey a unique sense of romance that only it can offer.

These days, dive watches are no longer strictly reserved for diving. People wear them as daily timepieces, whether for leisure or in the office. Is this at the back of your mind when you are designing the watch?
The premise of this watch is professional use, but we have also introduced a new clasp design that is suitable for daily wear. We hope that the wearers will experience the functionality in both professional and everyday contexts.

Once you are done with this story, click here to catch up with our August 2026 issue.