Seiko is expanding its Prospex line with two new additions to the Marinemaster series. These models trace their DNA back to 1965, the year Japan’s first diver’s watch debuted.
That original design famously accompanied Japanese Antarctic explorers in the late '60s, followed by the brand’s first 300-meter diver in 1968.
The 1968 diver's watch featured a high-beat automatic movement and 300 metres water resistance
Over the decades, this lineage has evolved through technical refinements and field testing, establishing Seiko’s diver’s watches as reliable instruments for both professional and recreational use.
The new Prospex Marinemaster 1968 Heritage Diver’s Watch in its standard production version (ref. HBF001) draws on the design codes of the 1968 model, retaining its characteristic silhouette with a screw-down crown positioned at 4 o’clock.
The stainless steel case, treated with a super-hard coating, measures 42.6 mm in diameter and 14.1 mm in thickness, and is paired with a matching bracelet equipped with a three-fold clasp featuring a push-button release and a slide adjuster allowing extension of up to 16 mm in 2 mm increments.
Water resistance is rated to 300 metres / 1,000 feet, while magnetic resistance reaches 4,800 A/m.
The black dial is designed to ensure optimal legibility underwater. Its fine-grained texture helps reduce reflections, while applied indexes with beveled edges catch the light from different angles.
Lumibrite coating on the hands and markers enhances visibility in low-light conditions.
A ceramic bezel insert, here in black, contributes to durability and scratch resistance, while the dual-curved sapphire crystal features an anti-reflective coating on the inner surface.
Powering the watch is the automatic Calibre 8L45, operating at a frequency of 28,800 vibrations per hour (4 Hz) and offering a power reserve of approximately 72 hours.
Developed as one of Seiko’s high-end mechanical movements, it uses Spron alloys for both the mainspring and hairspring.
The movement is regulated to a daily rate of +10/-5 seconds. To improve durability, the screw-down crown is integrated into a separate structural component within the case, allowing for easier servicing if needed.
Alongside this model, Seiko presents the Prospex Marinemaster 1968 Heritage Diver’s Watch JAMSTEC Limited Edition (ref. HBF002), created in collaboration with Japan Agency for Marine-Earth Science and Technology (JAMSTEC), a partnership dating back to the 1980s.
The partnership includes real-world testing, such as the 1983 deployment of professional diver’s watches rated to 600 metres aboard the SHINKAI 2000 research submersible.
The limited edition shares the same technical specifications as the standard model, including the Caliber 8L45 movement, 300m water resistance and overall case architecture, but introduces a distinct aesthetic inspired by polar exploration.
Its dial features a textured pattern evoking the path of an icebreaker through sea ice, rendered in a vertically oriented blue gradient that deepens towards the centre.
A thick, transparent coating enhances the sense of depth, while the blue ceramic bezel complements the dial and maintains the same resistance to wear.
The caseback is engraved with “JAMSTEC LIMITED EDITION” and an individual serial number, with production limited to 1,000 pieces.
The model also reflects JAMSTEC’s ongoing Arctic Research Program, which includes the upcoming deployment of the Mirai II, Japan’s first research vessel with icebreaking capabilities designed to operate in ice-covered seas.
Both versions of the Seiko Prospex Marinemaster 1968 Heritage Diver’s Watch will be available from July 2026 through Seiko Boutiques and selected retailers.
The standard model is priced at €3,800 / US$ 3,600, while the JAMSTEC Limited Edition is offered at €4,100 / US$ 3,900. seikowatches.com
The MM’s main issue is its height. It is an iconic watch that wears poorly because it is extremely thick. Seiko’s solution: increase the height by 0.1mm. Otherwise, well done.
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