The Seiko Prospex – What is the Baby Tuna and Why it is so Great!

When you see any watch Seiko puts out, there is a known quality attached to it. The Japanese watchmaker spares no details, never cuts corners, and ensures that each piece is perfect from the moment it rolls out of the factory’s floors. You will see the same extreme attention to detail in traditional Japanese swordmakers who make the finest katanas. A masterfully crafted one is flawless—and the same can practically be said about Seiko’s timepieces.

The Seiko Prospex Automatic Diver is one of those engineering pieces that scream of Japan’s dedication to their craft. Given the nomenclature of the “Baby Tuna” because of its offshoot design from the higher-tier MarineMaster Tuna, this watch is a true horological masterpiece. The Prospex line has some of the finest machinery in a diver’s watch range, and you know Seiko did not spare anything from this masterfully crafted timepiece.

Being the little brother of the Tuna, this watch costs a bit less, but it still nonetheless has the specifications of a great dive watch. Seiko holds the honor of designing the dive watch, which is why they place extreme focus on the line.

The Baby Tuna’s Chunky Bezel, Dial, And Movement

Immediately, what stands out with the Baby Tuna is the brushed steel bezel that has boldly defined numbers at the 3, 6, and 9 o’clock positions, with a luminous ball at the 12 o’clock position. The bezel rotates with the numbers 15, 30, and 45 on their respective positions to signify the number of minutes a diver has before needing to resurface. The choice of a silver bezel with black lines makes even darker dives much easier thanks to its great visibility when a light is shone on it.

The dial shows off the same kind of energy on this model, showcasing its large and defined luminous icons at each hour mark and a double-sized one at the 12 o’clock position. With a dark blue dial tone, the luminous marks shine brightly in the foreground for amazing visibility in the dark.

The hands are extremely unique, sporting a luminous stubby hour hand that does not cover any of the luminous markings, nor the minute indicators underneath them. The minute hand is the same as most watches, luminous and of a larger but thinner size. Meanwhile, the seconds hand is a bright yellow with a little luminous patch towards the end of the moving marker.

Topping off the dial is the existence of a day and date function, which is controlled by Seiko’s great automatic movement. The heart that keeps the Baby Tuna ticking is a 24 jewel automatic 4R36 made in-house by the Japanese manufacturer and holds a 41-hour power reserve.

The Baby Tuna’s Scallop-Reminiscent Case

At a whopping diameter of 50mm, the Baby Tuna is not exactly a baby at all. This dive watch is for bigger wrists, with the size needing to be quite large for added visibility underwater. A 50mm watch will stand out anywhere you go, and the design is slightly curved, reminiscent of a scallop to keep things comfortable while worn. The crown is uniquely placed at the 4 o’clock position with a screw-on design for maximum watertight sealing.

The case has no protruding lugs, giving the case a smooth feel all around, which is a necessity for divers to avoid snagging on anything while deep down underwater. Its bezel is easy enough to rotate, producing a satisfying clicking sound that isn’t obtrusive with each movement. With the ability to reach an impressive 200 meters underwater, this watch means serious business.


For a watch that is bold, has amazing features, and was constructed by the master craftsmanship of the best Japanese engineers and watchmakers, it does not get talked about enough. You will never go wrong when it comes to buying a Seiko watch—and with people not giving the brand enough credit, it is practically a sin that these timepieces don’t get enough support! When dealing with anything related to Seiko mod parts and creating your very own personalized timepiece, SeikoMods is your premium option. Whether you have an SKX, a Baby Tuna, or a 5KX, we have the best mod parts that will surely convert you to the cult of Seiko and its amazing moddable qualities. Get in touch with us and browse through premium mod parts for your Seiko today!

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