To celebrate 60 years of dive watches, Seiko is diving into the deep end with three additions to the Prospex range: the 60th Anniversary Marinemaster Professional (SLA081), 1968 Heritage Diver GMT (SPB509), and 1965 Heritage Diver (SPB511). Whether you’re a die-hard Seiko collector or simply a looking for an affordable, high quality diver, all three are distinct enough from their stablemates to be worth a look.

But as exciting as the watches are, they’re arguably overshadowed by something simple yet significant, a feature Seiko enthusiasts have been requesting for a long time: a bracelet with a micro-adjustment clasp that can be resized on the go by up to 15 mm.

The 1968 Heritage Diver GMT SPB509 (left), and 1965 Heritage Diver SPB511

Initial thoughts

In Western culture, significant anniversaries like the 25th, 50th, and 100th tend to be celebrated with great fanfare. In contrast, Japanese culture (and also widely East Asian culture) emphasises the 60th birthday – kanreki in Japanese – which also coincides with the completion of the traditional 12-year zodiac cycle. In this context, it’s worth looking closely at how Seiko is choosing to celebrate this milestone.

The 1965 and 1968 Heritage models are powered by the well-known cal. 6R-series movements, which offer a 72-hour power reserve. While the pair are essentially variants of existing watches with new wave-stamped dials, the massive Marinemaster is the standout, and an entirely new model.

The wave pattern dial of the 1965 Heritage Diver SPB511

The Marinemaster features a monobloc titanium case that is just over 45 mm wide and 16 mm thick. Seiko enthusiasts will appreciate the proprietary construction of the Marinemaster that’s similar to that found in Seiko’s iconic “Tuna” dive watches.

And the Marinemaster also takes things up a notch in terms of mechanics, and features the new top-of-the-line cal. 8L45 which also runs for 72 hours but does so at a higher 4 Hz beat rate for extra rate stability in the face of shocks.

The Marinemaster Professional SLA081

The Prospex range is known for being a good value, and that’s obviously the case for the 1965 and 1968 Heritage models, which cost US$1,400 and US$1,750, respectively.

The high-spec Marinemaster is also an interesting value proposition, but it comes in at a hefty US$4,600, which might result in some initial sticker shock. This pricing is largely justified by the titanium case and bracelet as well as upgraded movement.

At long last, an adjustable clasp

Notably, all three models include a new adjustable clasp that can be adjusted through six steps, each of 2.5 mm, resulting in a total adjustment range of 15 mm. This will help wearers find an ideal fit, even if their wrists expand or contract throughout the day, and it also allows the bracelet to fit over a wetsuit.

With enthusiasts having long wanted such a clasp, especially since Seiko’s rivals already offer the feature, the new clasp shows that Seiko is listening to the market, and is hopefully a sign of similar things to come at Grand Seiko.

The new adjustable clasp should delight Seiko enthusiasts. Notably, it makes its debut in both steel and titanium.

Deep dive on the Marinemaster case

The Marinemaster is an enigmatic watch; there’s nothing else quite like it. It’s large, in excess of 45 mm, and rated to 600 m, similar specs to the Omega Seamaster Planet Ocean. Despite the immense size, the watch is surprisingly lightweight as it is almost entirely titanium, but upgraded with Seiko’s “super-hard coating” that boosts scratch resistance.

But unlike the Planet Ocean, the Marinemaster features a monobloc case and L-shaped gaskets capable of preventing the ingress of helium gas during saturation diving, eliminating the need for a helium release valve. This construction was pioneered by the 600 m “Tuna” dive watch of 1975 conceived for professional divers working in pressurised environments where the atmosphere is saturated with inert gases like helium.

Like its historical predecessors, the Marinemaster features a monobloc case; the movement is inserted from the front.

Another interesting aspect of the Marinemaster’s case is the way the bezel is attached to the case. Instead of being press-fit or attached via screws in its rim, the bezel is held securely in place by a pair of retaining clamp in between the lugs that are secured onto the case from the back.

This unusual construction makes the watch something of a hybrid between standard Marinemaster models and the “Tuna” divers that feature an outer case to protect the inner case and bezel.

The Marinemaster features an unusual case construction.

The Marinemaster’s bezel insert is made of steel coated in diamond-like carbon (DLC), as opposed to the more-common aluminum or ceramic. This combination offers the look of ceramic – the coating gives it six times the hardness of steel – but the durability and cost-effectiveness of steel.

The 1965 and 1968

The 1965 and 1968 models sit at the more affordable end of the spectrum. The 1965 model is based on the 62MAS diver and its distinctive flat-fronted case, while the 1968 is inspired by the 1968 professional diver’s watch. The two are based on existing models, but facelifted with wave-patterned dials inspired by a traditional Japanese motif.

The Prospex 1965 Heritage Diver’s Watch SPB511

Both models are presented in stainless steel finished with  “super-hard coating” that results in superior scratch resistance. The two are powered by 6R series movements, a family of workhorse automatic movements widely employed in the Prospex range. The calibres have a useful 72-hour power reserve.

The 1968 Heritage Diver’s GMT SPB509 is notable for being both a dive watch and a second time zone. However, the GMT function is an independently adjustable 24-hour hand, also known as a “caller” type GMT, as opposed to an “true” GMT with an adjustable local-time hand.

The 1968 Heritage Diver’s GMT SPB509

Key facts and price

Seiko Prospex Marinemaster Professional Diver’s Watch 60th Anniversary Limited Edition
Ref. SLA081

Diameter: 45.4 mm
Height: 16 mm
Material: Titanium and stainless steel
Crystal: Sapphire
Water resistance: 600 m

Movement: Cal. 8L45
Functions: Hours, minutes, seconds, and date
Winding: Automatic
Frequency: 28,800 vibrations per hour (4 Hz)
Power reserve: 72 hours

Strap: Matching bracelet

Limited edition: 600 pieces
Availability: Starting July 2025
Price: US$4,600

Seiko Prospex 1968 Heritage Diver’s GMT 60th Anniversary Limited Edition
Ref. SPB509

Diameter: 42 mm
Height: 13.3 mm
Material: Stainless steel
Crystal: Sapphire
Water resistance: 300 m

Movement: Cal. 6R54
Functions: Hours, minutes, seconds, date, and GMT
Winding: Automatic
Frequency: 21,600 vibrations per hour (3.5 Hz)
Power reserve: 72 hours

Strap: Matching bracelet

Limited edition: 6,000 pieces
Availability: Starting June 2025
Price: US$1,750

Seiko Prospex 1965 Heritage Diver’s Watch 60th Anniversary Limited Edition
Ref. SPB511

Diameter: 40 mm
Height: 13 mm
Material: Stainless steel
Crystal: Sapphire
Water resistance: 300 m

Movement: Cal. 6R55
Functions: Hours, minutes, seconds, and date
Winding: Automatic
Frequency: 21,600 vibrations per hour (3.5 Hz)
Power reserve: 72 hours

Strap: Matching bracelet

Limited edition: 6,000 pieces
Availability: Starting June 2025
Price: US$1,400

For more information, visit seikowatches.com.

This was brought to you in partnership with Seiko.