The Seiko Tuna began as a practical answer to a saturation diver’s complaint: Seiko’s existing 300m watch could not cope with the conditions of deep-sea work. Seiko introduced the Professional Diver’s 600m in June 1975, pairing a titanium case with a protective outer shroud and a design intended for demanding underwater use. “Tuna” came later as a nickname for its cylindrical, can-like shape—not from any fish-related feature.
What is a Seiko Tuna watch?
“Tuna” is the familiar name for a family of Seiko professional dive watches distinguished by a cylindrical case and an outer protector, or shroud. The original watch was officially called the Professional Diver’s 600m, not the Tuna. Seiko’s design account says the can-like form inspired the “Tuna Can” nickname; Seiko’s anniversary history also uses “Tuna” for the watch.
| # | Preview | Product | Price | |
|---|---|---|---|---|
| 1 |
|
SEIKO SRPF03 Automatic Dive Watch for Men - Prospex Special Edition | $440.00 | Buy on Amazon |
| 2 |
|
SEIKO SRPL53 Automatic Diver Watch Men's Prospex - Green | $520.00 | Buy on Amazon |
| 3 |
|
Seiko 22mm Width Diver for Urethane watchband DAL1BP | $25.40 | Buy on Amazon |
The unusual silhouette reflects the original brief. Seiko describes the outer protector as a protective element designed to reduce the risk of ropes or other objects catching on the watch during deep-sea work. Its lugless outline, shroud and case were conceived as parts of a functional design, rather than as decoration added to a conventional diver’s watch.
Why did Seiko develop the original 600m diver?
In 1968, Seiko received a letter from a professional diver who described working at 350m with a diving bell. The letter, reproduced in Seiko Museum Ginza’s historical account, said Seiko’s existing 300m watch was not fit for those conditions. The writer is not named in the museum account, so the complaint is best understood as an unnamed working diver’s report, not a named endorsement.
The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →#1 Best Overall
- WATER-RESISTANT: these water-resistant men's dive watches are ISO scuba-approved to depths of 200 meters
- AUTOMATIC: these self-winding, automatic men's watches are powered by your movement, with a power reserve of 41 hours
- STAINLESS STEEL: features a durable 43.8mm stainless steel watch case and bracelet.
- LUMIBRITE DISPLAY: this men's automatic watch features a highly-legible display with LumiBrite hands and markers
- 4R35 CALIBER: equipped with the reliable caliber 4R35 automatic movement, this accurate men's watch keeps precise time
Seiko’s response was to rethink the watch for saturation diving, rather than simply increase the water-resistance figure on its existing design. The museum account is attributed to Taro Tanaka, the development leader and designer of the Professional Diver’s 600m. Tanaka later described the first-generation watch as the result of pursuing a new design in response to customers’ unfiltered needs.
What made the 1975 Professional Diver’s 600m different?
Seiko launched the original Professional Diver’s 600m in June 1975. Its one-piece titanium case and outer protector formed a distinctive, robust-looking package, while a specially developed L-shaped gasket was intended to prevent helium from entering the watch without relying on an escape valve. Seiko also equipped it with an accordion-style strap.
Rank #2
- STAINLESS STEEL CASE built to endure with style, making this watch your perfect daily companion
- AUTOMATIC MOVEMENT for seamless precision in every tick of this watch
- SCRATCH-RESISTANT CRYSTAL to maintain a pristine look even with daily wear and tear on your watch
- LUMINESCENT HANDS for effortless readability in low-light conditions, ensuring you never miss a moment with this watch
- WATER RESISTANT DESIGN ensuring your watch is ready for any adventure, rain or shine
The shroud’s shape was part of the engineering response: it provided protection and was designed to help keep ropes and other objects from snagging during deep-sea work. Seiko Museum Ginza says the development involved more than 20 patents, utility model and design registrations. The watch was rated to 600m, a specification that belongs to this original model and should not be confused with the higher rating of a later development.
How did the Seiko Tuna evolve?
| Year | Development | Key distinction |
|---|---|---|
| 1975 | Professional Diver’s 600m launches | Mechanical movement, titanium case, outer protector and 600m rating. Seiko Museum Ginza records an initial Japanese retail price of ¥89,000 in June 1975. |
| 1978 | Cal.7549 quartz version | The line shifted from a mechanical movement to quartz. Projections on the outer body at 12 and 6 o’clock were shortened to reduce weight, and the hands were changed to improve visibility. The museum records a Japanese retail price of ¥120,000 at the time. |
| 1986 | Cal.7C46 1,000m development | The outer-body material changed to high-strength black ceramic and the stated pressure-resistance rating rose to 1,000m. The museum records a Japanese retail price of ¥133,000 at the time. |
The prices in the table are historical Japanese retail prices in nominal yen, not current prices or converted estimates. The 1978 quartz transition and 1986 1,000m development are distinct stages in the family’s history; neither changes the original Professional Diver’s 600m rating.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
What makes a Tuna different from an ordinary dive watch?
- A case built around a shroud: The outer protector gives the Tuna its recognizable shape and serves a protective, snag-reduction purpose described by Seiko.
- A saturation-diving origin: The design followed a report that an existing 300m watch could not meet a professional diver’s working conditions.
- A specific helium approach: Seiko says the original’s L-shaped gasket was designed to prevent helium ingress without an escape valve.
- A lineage, not one specification: The family includes mechanical and quartz movements and different stated depth ratings. Sharing the Tuna nickname does not make every model interchangeable or establish suitability for professional diving.
Which Seiko Tuna models are available now?
Seiko’s UK Prospex Diver’s collection lists Tuna as a collection category, confirming that the name remains part of the brand’s current product taxonomy. That does not establish which references are currently in stock or sold in another country. Availability and model selection vary by market and over time, so check the relevant Seiko market page for live listings and the exact model specification.
Modern examples span different constructions and movements. A 2025 overview by Fratello discusses the quartz SBBN047 and automatic monocoque examples SBDX038/SLA042, but its account of the international lineup is dated and is not proof of current availability in any particular market. When comparing references, check movement, water-resistance rating, case and shroud materials, construction, dimensions, and whether the watch is an original-era model, a reissue or a current interpretation.
Quick Recap
Sources and historical context
- Seiko Museum Ginza: “Professional Diver’s 600m Watch: The Black Face of the Deep Sea” — development account, historical specifications, dates and Japanese prices.
- Seiko Watch Corporation’s 2020 anniversary release — the complaint context, titanium case, L-shaped gasket, strap and Tuna name.
- Seiko Design 140: “1975 The Professional Diver 600m” — the saturation-diving purpose and protective design.
- Seiko Design: “The Tuna Can Story” — the nickname and can-like form.
- Seiko Boutique UK: Prospex Diver’s collection — official collection taxonomy for the UK market.
- Fratello Watches’ 2025 monocoque Tuna overview — secondary discussion of selected modern references.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
