Deep Dive Review of the Seiko Prospex Tuna Can Watch
Ignatius Quiaoit
14 October 2023 | 11 min read
As with many hobbies, scuba diving started as a military need. With the onset of various navies and marine forces, the need to conduct underwater operations pushed militaries around the world to develop instruments that could handle the pressures of the ocean.
With innovations and the introduction of more affordable equipment, the hobby of scuba diving blew up in the 50’s. Now, almost everybody can experience the wonders of the ocean at a relatively attainable price point.
Watch brands jumped on the new hobby and created watches that could accompany both professional and hobby divers.
However, as man’s thirst for adventure drove them deeper and deeper, brands needed to catch up (or sink) to the level that these new divers were going. Thus, the saturation dive watch.
Among the current choices of saturation dive-ready watches is the Tuna Can Seiko.
Join us as we take a dive through the history of the Tuna Can in this article.
I. Short History of Seiko
The Seiko brand started as the “K. Hattori” shop in Tokyo, Japan. Founded in 1881 by Kintaro Hattori, the brand started by selling the watches of other brands.
Coming from his apprenticeship and experience with several other watch brands like F. Perregaux & Co., Hattori then moved to watch manufacturing under the new name, Seikosha.
Coming out with various pocket watches, the brand developed Japan’s first wristwatch in 1913, the Seiko Laurel.
What followed was a series of innovations that would shock the watch world. From in-house movement firsts to beating the Swiss at their accuracy trials, Seiko has earned its right to become one of the juggernauts of the watch world.
Among the technical innovations the brand has brought forth, none of them were as groundbreaking as the introduction of the quartz movement. What followed was none other than the infamous Quartz Crisis.
What started as a pursuit of high-accuracy battery-powered movements turned into a mammoth of an upset for the watch world.
Brands scrambled to find an alternative to their current (outdated) mechanical offerings.
What set Seiko apart was their innovation in not just creating the quartz movement but in manufacturing it in high quantities to call for lower and more affordable prices.
For a more in-depth look at the history of the Seiko brand, we point to our article Seiko Takes on the World: Japanese Dragon vs Swiss Monopoly.
II. History of the Seiko Prospex Tuna Can
In 1965, Seiko presented their first purpose-built dive watch. This came in the form of the 62MAS, Seiko’s first diver’s watch. Featuring an automatic movement and a water resistance of 200m, this was Seiko’s first foray into purpose watches after trailing behind the Swiss for a good amount of time.
However, in 1975, a saturation diver from the historical naval town of Kure City in the Hiroshima Prefecture of Japan complained to Seiko that their current dive offerings were not up to par with the profession of saturation diving.
For one, saturation dives require professional divers to stay underwater for longer periods, all while experiencing more extreme conditions than the normal scuba diver.
These circumstances mean that saturation divers need a watch that can withstand the high pressure of saturation diving.
These comments rattled Seiko.
One of the complaints thrown was the susceptibility of the current watches to the helium gas problem. This is something that newer and more modern saturation-ready dive watches have already addressed.
Seiko engineers, led by Ikuo Tokunaga, set out to produce a watch that would fit all the needs of a saturation diver. What came out was something new and magnificent.
Nicknamed the “Tuna,” the Seiko 6159-7010 Professional looked like nothing else on the Seiko lineup. This was the first Seiko Tuna.
Protected by a titanium case material and enshrined in a titanium and ceramic shroud, the Seiko Tuna boasted a water resistance of 600m.
This is triple the water resistance of the already famous Seiko 62MAS. To make the watch more adherent to the wrist of divers, Seiko introduced a vented rubber strap to go with it.
Ensuring that the watch could reach 600m was no easy feat. To develop such a capability, the engineers at Seiko introduced an L-shaped helium gasket. What does this exactly do?
During dives, when a diver goes deeper, there is a build-up of helium gas within pressurized areas. One of these areas is the inside of a mechanical watch.
Once this build-up occurs, there is a need to decompress the inside of a watch to ensure the integrity of the case.
The helium escape valve does exactly this. Upon a pressure difference, the valve will automatically open to allow the release of helium gas.
This, matched with the all-black casing and darkness associated with the use of titanium materials, gives us a whopping image of a watch. The original Tuna came in a 50.5 mm diameter, definitely something humongous at the time of its release.
Giving the Tuna its name is the case that shrouds the movement within. This case provides the wearer with only two access points to move the bidirectional dive bezel.
This ensures that the dive bezel will not accidentally move while in use underwater, providing any wearer with the confidence needed in their instruments.
Protecting the movement is undoubtedly important for Seiko, especially for the movement they chose to house within it. This movement is the 6159A, a Grand Seiko-derived 36,000-vph automatic movement.
That is right. Seiko decided to up the ante with this dive watch by including a high-beat movement usually reserved for Grand Seiko dress watches.
Now, the Tuna has been in production ever since its inception. The collection has expanded and has been featured in various film showings.
Of course, who could forget the action-packed and alien-filled movies of Arnold Schwarzenegger? Yet, why mention Arnie without mentioning the watch that was given the same name, the Seiko H558-5009, the Seiko Arnie?
Debuting in Schwarzenegger’s movies Commando (1985) and Predator (1987), the Seiko Arnie is one of Seiko’s own quartz watches that hit the big screen.
Looking minuscule compared to the monstrous arm of Schwarzenegger, the watch braved many battles and fights, all while the second hand kept on ticking.
The Arnie was introduced to the Japanese market with an alarm and chronograph function and was the first hybrid diver to go 150m underwater. During the watch’s development, Seiko engineers tested the watch to withstand temperatures of -40C and 60C.
It was also a watch that was able to scale up Everest along with the explorations of both the North and South Pole. The Arnie quickly became a popular Seiko Tuna.
What separates the Arnie from other special Tuna Cans is the fact that the crown is located at 3 o’clock instead of the usual 4 o’clock position.
When using the Seiko Arnie, the upper left button on the left side of the case activates the digital display light. The lower left pusher allows you to scroll through the various functions like the date, local time, second timezone, alarm, and chronograph.
From these features alone, we can see that the Seiko Tuna Can packs a lot of features.
To change the setting of any function, you first scroll to the function you want, then unscrew the crown to the second stop, and turn the crown to adjust the setting. Pulling out the crown to the farthest position will let you change the hands of the watch.
In 2019, Seiko reintroduced the Arnie with the Seiko SNJ025. Sporting a solar movement, the watch continues the legacy of professional diving standards from the original Arnie.
With its 47.8mm black durable case, the watch showcases the manufacturing process that Seiko possesses in producing excellent value timepieces.
Known for his early use of Rolex Submariners and his current brand partnership with Omega, James Bond can be seen wearing an example of the growing power of Japanese watchmaking.
Sir Roger Moore can be seen wearing several Seikos throughout his reign as 007. In For Your Eyes Only (1981), Moore was filmed wearing a Seiko 7549-7009 “Golden Tuna.”
Although less refined as compared to the previous Rolex showings, this marks the certain departure that watchmaking was experiencing at the time.
Interestingly enough, this specific piece seemed to be owned by Sir Roger Moore himself. It was seen on his wrist in another movie he did called North Sea Hijack (1980).
Getting its name as the “Golden Tuna,” the Seiko 7549-7009 sports golden accents on the crown, inner case, screws, and case back.
This is a departure from the usual black plastic or stainless steel that we see with the previous iterations of the Tuna Can.
III. Current “Tuna Can Seiko” Selections
Aside from the current iteration of the Seiko Arnie, Seiko realized the potential of the Tuna Can design and has spawned several new collections that share the same design elements. The brand has released various Tuna models.
For one, we have the Seiko SUT403P1. Moving away from the super-utilitarian use of the original Tuna Cans, the SUT403P1 is part of Seiko’s “Street Series.”
This collection takes inspiration from the design of the original Tunas, but updated the look and feel to give it a more apt sense of the urban, according to Seiko.
With that, the SUT403P1 sports a smaller case size of 38.7mm. This makes the watch wearable on even smaller wrists. Included with the watch is a mix of blue and khaki colour coding. Seiko gave the watch a blue dial, with the hour markers sporting some khaki lume.
The dive bezel is split between blue and khaki, with the first 20 minutes having the khaki and the remaining 40 minutes the blue. This gives the watch a more subtle and relaxed feel, a certain contrast to the overall case size of the watch.
The timepiece is powered by the V131 solar movement and has a depth rating of 200m.
To maintain legibility, Seiko has often used black dials to differentiate the hour and minute hands properly. This ensures the diver that they can see the time as best as they can.
However, Seiko has lately been experimenting with various dial options and colours (one should look no further than their numerous limited editions). One of these is the SRPH77 Special Edition, sporting a special “Save the Ocean” dial.
The Save the Ocean Initiative is an advocacy dedicated to the preservation and conservation of our planet’s oceans.
Seiko has been a long supporter of this initiative with their various limited editions, as is the case here.
The limited edition dial shares the features of the deep blue ocean with its gradient ocean blues and brush strokes.
A closer look at the dial shows us the waves and textures that go around the dial, showcasing the various contours that an ocean may have.
Penguin silhouettes are strewn across the dial, showcasing the initiative’s focus on the conservation of marine life.
The watch is powered by the automatic 4R35 movement with 41 hours of power reserve. The 4R35 movement has been touted as the replacement to the legacy workhorse movement of early Seiko divers, the 7S26.
The watch comes in the usual Tuna Can case design with a 43.2mm case diameter with a hardlex crystal.
Following famous nicknames and naming conventions, Seiko released the SBBN047, otherwise known as the “Darth Tuna.” Following the design formula of the Tuna Can but coming in a larger format, the Darth Tuna comes in at 49.4mm.
However, with the Tuna Can case design, there are nonexistent lugs that make every Tuna Can Seiko look smaller than they really are.
The Darth Tuna receives its name from the colourway present with the watch. The watch comes with a monochromatic black look.
From the case to the bezel to the black dial, almost everything is black. The monotony is broken up by the presence of the white-lumed hour markers and minute and hour hands. The white chapter ring divides the black bezel from the rest of the dial.
The Darth Tuna is rated to withstand a total of 1000m of water resistance. Powering the Darth Tuna is the Seiko 7C46 quartz movement. This is the most common movement used in the Seiko Tuna Cans.
The movement has a rated life of five years on a single battery. The rated accuracy of the watch is +/- 15 seconds a month.
This is better than most mechanical movements out there.
Sadly, the Darth Tuna is a JDM-specific model, meaning that this collectable watch is even more collectable than others.
Although the Tuna Can is already one of the more feature-ridden watches within Seiko’s lineup, there are Tuna Cans within the collection that up the ante of everything that they already offer. One of these is the Seiko SBDX014, otherwise known as the “Emperor Tuna.”
Seiko did not cheap out with any of the design elements with the Emperor Tuna.
Seiko pulled out the titanium materials to shroud the casing and movement while also encasing the entire thing in a rose-gold-plated ceramic case with the rose gold following the crown and the screws around the watch.
This watch is rated to be a Marinemaster, meaning that this watch showcases the best of the best watchmaking that Seiko develops for their dive watches.
One of these things is the fact that the Emperor Tuna is rated for 1000m.
To house all the technology and high-quality watchmaking, the Emperor Tuna measures 52.4mm in case diameter.
The watch is powered by one of the mid-range movements within the Seiko lineup, yet, even if it is the mid-range, the movement is derived from the Grand Seiko calibre 9S55 movement.
That movement is the caliber 8L35. The 8L35 is an entirely proprietary movement from Seiko, developed and manufactured at their Shizuku-ishi Watch Studio.
The movement beats at 4Hz and is regulated to +15 / -10 seconds a day.
IV. Summary
Tackling the Tuna Can Seiko gives us a glimpse into the design thinking that is within the Seiko brand. From the start, they developed the amazing 62MAS that featured dive specifications enough for divers at the time.
Yet, when presented with proper criticism of their current specifications, Seiko decided to do the innovative thing and develop an even better watch.
Thus, the Seiko Tuna Can was born. Featuring a case design that gave birth to its own nickname, the watch pushed the technical boundaries of saturation dive-ready watches at the time.
Some people can judge the success of a watch through the numerous iterations that have come about after the original watch’s inception. With that measure, the Tuna Can Seiko exceeds every expectation and standard.
The numerous models and even special editions that this watch has spawned are too many to list in one article.
Not to mention the cultural significance the watch has in terms of the big screen, being showcased in various films.
The Seiko Tuna Can is as iconic as the people who wore it. If anyone is thinking of purchasing or collecting a specific line within the Seiko lineup, what better collection to get into than the Seiko Tuna Can?