It’s spelled Seiko, but it’s all about the sea. The Japanese brand, which celebrates its 145th anniversary in 2026, has a history linked to underwater exploration dating back over 60 years. Since the mid-1960s, there have been numerous models dedicated to professional divers; an expansion of the collection that has reflected not only the growth of technical expertise but also Seiko’s passion for the sea and its collaboration with organisations, associations and figures linked to the ocean and exploration. Among these is JAMSTEC, the Japan Agency for Marine-Earth Science and Technology, with whom, since the 1980s, Seiko has established a lasting partnership based on shared values, leading to the creation of some of the timepieces most favoured by professional divers.
A comprehensive partnership, born of a deep affinity of purpose—such as exploration, the pursuit of performance and environmental protection—which unites Seiko and JAMSTEC and results in a mutual exchange of experience and knowledge. On the one hand, the professionals at the Japanese agency have access to state-of-the-art watchmaking technology to accompany them on their missions; on the other, the brand has the opportunity to test its timepieces in extreme conditions, gaining useful and valuable insights for the development of ever more reliable and advanced watches.
In this article, we will discuss the two new models in the Marinemaster series, the flagship of Prospex. The first is inspired by the spirit of exploration shared by JAMSTEC and Seiko and is the result of the collaboration with the Japan Agency for Marine Earth Science and Technology, whilst the second is a model in continuous production. We will then briefly retrace the history of the partnership between the brand and the Japanese agency, highlighting some of its most significant milestones and the watches that have defined them.
PROSPEX MARINEMASTER 1968 HERITAGE DIVER’S WATCH JAMSTEC LIMITED EDITION
Within the Prospex collection, the Marinemaster series is synonymous with performance and meticulous attention to aesthetic detail, choice of materials and mechanical excellence. All these characteristics are fully expressed in the new Prospex Marinemaster 1968 Heritage Diver’s Watch JAMSTEC Limited Edition, reference HBF002J1. As the name suggests, the model draws inspiration from the first Japanese watch water-resistant to 30 bar, featuring a high-precision hi-beat automatic calibre with a frequency of 10 vibrations per second, which the manufacturer created in 1968. It incorporates the crown at 4 o’clock, the design of the hour markers and hands, and the ergonomic shape of the case from that model.
The new Marinemaster, developed in collaboration with JAMSTEC, is a robust diver’s watch featuring a 42.6 mm diameter stainless steel case, 14.1 mm thick, with a combination of polished and satin-finished surfaces. These are compact dimensions for a professional diving watch, certified water-resistant to 30 bar. This achievement has been made possible thanks to the experience gained over decades through the partnership with the Japanese agency, which has enabled the creation of ever more high-performance timepieces. However, what makes the HBF002J1 model unique is not the case.
Rather, it is the textured dial, reminiscent of the wake left by an icebreaker as it ploughs through the Arctic ice. The colour gradient, running vertically, intensifies towards the centre, where the colour deepens from a very light, almost white blue on the outer edge to a deep blue. The dial is finished with a thick transparent coating and then polished, evoking the crystalline depths of the Arctic Ocean.
The icebreaker’s wake symbolises the way in which Arctic research paves the way for the future; in a sense, it also recalls the Japanese Antarctic research expedition in which Seiko participated between 1966 and 1969, with the first Japanese diver’s watch in history, created in 1965. The beauty of the dial is enhanced by the polished blue ceramic bezel, which is highly legible and scratch-resistant.
THE WATCH’S DETAILS
The idea of the icebreaker is no coincidence. It is in fact inspired by the Mirai II, the first Japanese Arctic research vessel with icebreaking capabilities launched by JAMSTEC exactly one year ago, on 19 March 2025, and due for completion this coming autumn. A robust and technologically advanced vessel, just like this diver’s watch.
In addition to the durable case and the legible, elegant and compact dial, the robustness of the Prospex Marinemaster 1968 Heritage Diver’s Watch JAMSTEC Limited Edition is also evident in the solid three-row steel bracelet, featuring alternating satin-finished and polished surfaces, which are also found on the case. It is secured to the wrist by a folding clasp with a safety and release button, which allows for easy adjustment up to 16 mm, in 2 mm increments, by pressing an internal button. Even when the clasp is closed, the extension can be retracted, ensuring comfortable and effortless operation.
As with any self-respecting professional diver’s watch, the case back is screw-down and the crown is screw-down. The rotating bezel is unidirectional and the sapphire crystal is dual-curved, ensuring further resistance to underwater pressure.
The case, crystal and dial protect the 8L45 calibre, an automatic movement with a manual winding option, an evolution of the 8L35. Seiko also uses it in other models in its high-end range, such as the King Seiko Vanac, a testament to the excellence of its craftsmanship and performance. We are talking about 28,800 vibrations per hour for a 72-hour power reserve but, above all, a precision of +10/-5 seconds per day, a performance of the highest calibre.
PROSPEX MARINEMASTER 1968 HERITAGE DIVER’S WATCH: HOW IT’S MADE
Alongside the HBF002J1 model, a limited edition of 1,000 pieces, Seiko has unveiled the Prospex Marinemaster 1968 Heritage Diver’s Watch, model HBF001J1, a standard model and therefore not limited, which continues the tradition of excellence of the Marinemaster line. The technical specifications and design features are the same as those of the HBF002J1 model.
The case is made of stainless steel, with a polished finish on the sides and a satin-brushed finish on the lugs, measuring 42.6 mm in diameter and 14.1 mm in thickness. Water-resistant to 30 bar to allow for professional diving, its design, like the limited edition, is inspired by that of the 1968 Diver’s Heritage, with its characteristic slender silhouette and crown positioned at 4 o’clock. It is worth noting that, in both models, the crown is not screwed directly onto the case but is attached to a separate internal component, to facilitate any replacement work.
The steel bracelet has the same design and functionality as that of the HBF002J1 model, particularly regarding the one-push adjustable clasp: thanks to its sliding mechanism, the bracelet can be adjusted to the wrist easily and precisely. The movement housed within is once again the 8L45 calibre with a 72-hour power reserve, whose accuracy is certified to +10/-5 seconds per day.
The difference from the limited edition lies entirely in the dial, which here features a classic and functional design, engineered to ensure optimal readability underwater and in low-light conditions. It is in fact black, satin-finished, with a fine-grain finish, a texture that reduces glare and optimises the visibility of the contrasting hour markers and hands, both coated with premium Lumibrite, which guarantees long-lasting luminosity and exceptional readability even in low light. The unidirectional bezel is also black, with a black ceramic insert and a Lumibrite-coated dot.
SEIKO, JAMSTEC AND WATCH TESTING
As mentioned at the start, this limited-edition model stems from the long-standing collaboration between Seiko and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Over the years, several Seiko divers’ watches have undergone rigorous underwater durability tests, proving their reliability at great depths.
The first tests were carried out in 1982, when JAMSTEC subjected several diving watches to saturation diving at 300 metres. On that occasion, Seiko’s Diver’s Professional 600m proved to be up to ten times more resistant to helium than watches from other brands. Buoyed by these results, the following year JAMSTEC went a step further, mounting two Seiko Diver’s Professional 600m watches on the outer hull of its Shinkai 2000 research submersible. Both had been designed to withstand depths of up to 600 metres, but retained their legibility and accuracy even at -1,062 metres.
In 2014, two 1,000m diving watches – in quartz and mechanical versions – were subjected to an even more extreme test. Attached to the outer hull of the KAIKO 7000 II, a remotely operated submersible, they descended even deeper, to3,000 metres, and continued to function perfectly.
In 2015, the latest version of the 1000m professional diver’s watch underwent a durability and resistance test. The watch was attached to the robotic arm of the Shinkai 6500 research submersible, and for 16 hours and 40 minutes the crew manoeuvred the arm to a depth of around 1,400 metres. The timepiece confirmed its precision even under adverse conditions throughout the entire test. In Japanese, Shinkai means ‘deep sea’: Seiko drew inspiration from this for the dial pattern of the Prospex Marinemaster reference SLA081J1, created in 2025 to mark the 60th anniversary of the brand’s divers.
THE PARTNERSHIP BETWEEN SEIKO AND JAMSTEC
The partnership therefore has broader scope. It is, to all intents and purposes, a sharing of values and a concrete, reciprocal collaboration: for Seiko, it is a source of technical refinements and inspiration for new models; JAMSTECbenefits from Seiko’s active participation in its study and research programmes. One example is the Arctic research programme promoted by JAMSTEC through the National Institute of Polar Research of Japan, which conducts studies on environmental changes and monitors natural phenomena in the Arctic and Antarctic regions. This work aims to predict the impact of global warming on the environment, and Seiko Prospex contributes to it through the “Save the Ocean” initiative.
Every brand has its own sphere of experimentation and communication: Seiko’s lies in exploration in extreme environments, combined with a commitment to environmental conservation. The collaboration with JAMSTEC is a perfect embodiment of this, enabling the manufacturer to continually enhance the technical excellence of its watches, as is the case with the two new Prospex Marinemaster models.
PRICES AND CONCLUSIONS
In conclusion, we note that the price of the limited edition (the number of which is engraved on the case back) is €. 4,100, dropping to €. 3,800 for the version with a black dial and bezel. It is clear that, in the development of these watches, the collaboration with JAMSTEC is invaluable, given some of the Japanese agency’s objectives: to explore and understand the oceans, study the climate and its global changes, and monitor natural hazards.
JAMSTEC studies ocean currents, the ocean floor, deep-sea biodiversity and water chemistry; it plays a leading role in climate research and in observing earthquakes, tsunamis, volcanoes and the Earth’s internal dynamics to understand and anticipate disasters. These are all elements from which Seiko can draw useful insights to develop technical solutions that make its divers’ watches even more high-performing.
These are not merely sales pitches or good ideas for marketing and storytelling. They are important opportunities to develop a product through valuable synergies between two organisations which, ultimately, share the same goal: to work and study in order to offer tools and knowledge that can make a difference to people and the environment in which we live.
By Davide Passoni