Review: Seiko “Tuna” 55th Anniversary SLA041J1 (SBDX035) Prospex 1975 Dive Limited Edition

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This is the year of the Prospex for Seiko. In addition to this 55th Anniversary release, they also released a Street Series of 4 Prospex “Tuna” Urban Safari novelties covered the press release earlier today. Here, we examine the recreation of the original diving watches – the Prospex 55th Anniversary re-creations, and dive deep into the “Tuna” re-creation – the Seiko “Tuna” 55th Anniversary SLA041J1 (SBDX035) Prospex 1975 Dive Limited Edition.

Seiko Prospex 55th Anniversary Limited Editions

55 years ago, Seiko introduced its, and Japan’s, first ever diver’s watch. This was the 62MAS, which has now become an icon of the industry and a collector’s item. With an automatic movement and water resistance to 150m, it proved its reliability when it was used by members of the Japanese Antarctic Research Expedition from 1966 to 1969.

Seiko’s plan this year, celebrating 55 years of the Japan’s first diver watch is a re-creation of three of these icons. Offered in the Prospex 55th Anniversary collection are:

  • the SLA037J1, a re-creation of the 1965 original 62MAS which had a 150m depth rating, extended to 200m in the new model
  • the SLA039J1, a re-creation of the 1968 model, then and now capable of 300m air diving model
  • the SLA041J1, a re-creation of the 1979 “Tuna” saturation diving model, now capable of 1000m, an extension from the 600m of the original.

The 1965 and 68 re-creations are powered by the high beat 8L55 movement while the 1975 re-creation has a Caliber 8L35. Both movements were developed and assembled specifically for diver’s watches at the Shizukuishi Watch Studio.

All the re-creation pieces are limited editions of 1,100 pieces each, and will be rolled out throughout 2020 with SLA037J1 released in June, SLA039J1 in July and SLA041J1 in August. Though the final release dates may be delayed due to the COVID19 situation, as highlighted by a recent Seiko Press Release.

A special box set of all three are available with spare black straps, and limited to only 100 pieces.

While the designs of each of three models remain faithful to the historic models that they are based on, they have very much up-to-date specs and modern materials. In this review, we focus on the “Tuna” – the SLA041J1.

Seiko Prospex SLA041J1

Seiko tells of the story of a letter from Hiroshima, where the correspondent, a professional diver, explained that he could not find any watch which could withstand the stresses and strains he experienced when working at depths greater than 300m. This inspired Seiko engineers to work on such a watch, and the years of research development paid off in 1975 with the introduction of the world’s first titanium cased diver’s watch: the Professional Diver’s 600m. The first Tuna.

The case, dial and hands

The case of the SLA041 follows the formula of the Tuna watches since. The case construction and dial layout are loyal to the original, as are the huge bezel, the hour markers, the crown and the unique shroud which protects the case. The case is a one piece titanium case the shroud in zirconia ceramic. A material which is 7 times harder than the steel case which the shroud protects, and have been used in some iterations of the Tuna.

In comparison to the original 1975 model, the new dial has a light blue hue, which does not appear in our photographs, perhaps due to our lighting.

The original Tuna had a depth rating of 600m in a saturation environment, but several subsequent models have sported 1000m rated cases, and the new SLA041 is so rated to the 1km depth mark, as well as for saturation diving. As is normal for Seiko saturating diving watches, there is no helium escape valve, choosing to solve the problem of helium explosion by the use of an L-shaped gasket and ultra strong crystal and case construction.

The case is enormous, measuring 52.4mm wide, inclusive of the shroud and 17.2mm thick. However, it does not look out of place as it is intended to look massive, super strong and ultra robust with its intended usage.

The watch boasts of a magnetic resistance rated at 40,000 A/m (not directly comparable, but roughly equivalent to a magnetic flux density of 500 Gauss). This rating, while not as impressive as the 15,000 Gauss used Omega’s METAS protocol, is sufficient for it to be practical for diving applications. The dial is made of a massive piece of steel, and though the Seiko literature does not clarify, we assume a soft iron cage is used within the case to ensure the movement meets its anti-magnetic claims.

The dial layout is typical of a diving watch. Very simple with good clarity, the markers are very large, with a polished metal frame infilled with a huge dollop of Lumibrite. Legibility is excellent, both in the dark and in good light. Apologies, we forgot to take lume pics when we had our hands-on with the watch, but regular readers will not be unfamiliar with Seiko Lumibrite lumes. The hands are large, also infilled with Lumibrite.

The dial is made of pure iron to form the protection needed for the 40000 A/m magnetic resistance.

Lumibrite is a luminous paint, developed by Kenzo Nemoto in 1941. During World War II, he supplied aircraft and submarines with lumed gauges and meters. After the war, he had the idea use this product on clocks in civilian homes. It was not until 1993 when Nemoto commercialized the product as LumiNova, and licensed to the Swiss under the brand name Super-LumNova, now widely used in the watchmaking industry. The Seiko version, which also appeared sometime in 1993, is called Lumibrite.

The shroud in the new model is Zirconia Ceramic similar to the one used in the Emperor Tuna SBDX014. And the accordion style strap is thick, and very robust.

The movement – the Seiko C. 8L35

The movement used in the SLA041 is made in Seiko’s Shizukuishi Watch Studio. As is typical in a dive watch, especially one rated to 1000m for saturation diving, the case back is sealed and the movement is not visible.

These movements are found in many Seiko watches, including the other watches in the Tuna series and the Marinemasters. The movement is very well designed and executed to

The Seiko 8L35. Photo from, where more information is available.

However, we have had several opportunities to examine the 8L35 during our visit to the Seiko facilities. The 8L35 is mechanically identical to the 9S55, with a lower level of decoration and is not adjusted to the same levels. We found that the even though it is not at the level of the GS caliber, it is proficiently executed. Finishing is rated to be a very good engineering level. Overall the movement works very well, and is very robust. Accuracy is rated at -10/+15 seconds per day in normal temperature conditions (5-35 °C), but in our experience with other watches with the same movement, it typically leaves the factory with a tighter tolerance, and easily meet chronometer specifications.

The competitive landscape

We compare the Seiko to two of the most formidable diving watch brands on the planet – the Rolex and the Omega. Both designed for saturation diving, and both icons in their own right. Among the first diver watches to be made, both firms offer extraordinary products at a similar price point, but more than double of the S$6k that Seiko asks for the SLA041, which makes it a rather good value proposition.

Any saturation diving watch will face the formidable Rolex Sea Dweller (S$15,670) as a competitor. Rated to 1,200m with a massive 43mm Oystersteel case, the watch is legendary, with a strong history to back its claim to the crown. But as many readers have constantly reminded us, comparisons to Rolex sports watches are often moot, as the watches are very difficult to procure from an Authorized Dealer.

Omega Seamaster Ploprof 1200 (S$16,300 in titanium case and mesh bracelet) perhaps is a good representation from Omega. The watch is massive, and rated to 1200m, but sufficiently handsome to take some points in the good looks department. The current Ploprof (PLOngeur PROfessional – professional diver in French) is also a re-creation of an original saturation diving watch from 1970. The movement is the advanced Omega 8912 calibre with a Co-Axial escapement and Master Chronometer certification, approved by METAS, and interestingly is visible from the sapphire case back. The helium escape valve is a huge affair and balances visually with the equally large crown and crown guard on either sides of the case.

Closer to home, and from the same stable is the Grand Seiko Hi-Beat 36000 Professional 600m Diver’s SBGH257 (S$19,600), a saturation dive capable watch but is only rated to 600m. The finishing on the GS is, needless to say at another level, especially as it is executed in titanium and with the famous Seiko zaratsu technique. And equipped with the high beat Caliber 9S85.

Concluding thoughts

The overall fit and finish is excellent, and exudes an air of confidence and competency which is quite important for a diving watch, where one’s life may depend on it. Even in these days, where diving computers are the main instruments utilized.

For a watch this massive. There is no way to hide that bulk and it does stick out from the wrist quite a lot. But on the flip side, it does wear rather comfortably. In our testing, we found it to be totally in place on top of a diving suit (or so we speculate, having not donned a diving suit while trying on the SLA041), or even with casual clothing and used as a tool watch. We do think that the SLA041 is a bit expensive for a Seiko, but compared to the competition with similar features, one could perhaps make a case that the asking price is not excessive.

Seiko Prospex SLA041J1 (JP Ref SBDX035) Specifications

Caliber Number: 8L35
Movement Type: Automatic with manual winding capacity
Accuracy: +15 to -10 seconds per day
Duration: Approx. 50 hours

Case Material: Titanium with Ever-Brilliant Steel with shroud in Zirconia Ceramic
Crystal: Sapphire
LumiBrite: Lumibrite on hands, indexs and bezel
Band Material: Silicone

Other Details
Water Resistance: 1000m / 3300ft for saturation diving
Case Size
Thickness: 17.2㎜
Diameter: 52.4㎜
Length: 53.5 ㎜

Other Specifications
Limited Edition – 1100 Pieces World Wide
Magnetic resistance:40,000A/m
One-piece structure
Screw-down crown
Serial number engraved on the case back
Unidirectional rotating bezel

Other Features
26 jewels
Date display
Stop second hand function


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