The Seiko Tuna line has been gradually refined and upgraded over the last few decades, and now being fair to acknowledge it as one of Seiko’s most solid collection
Seiko Tuna is the name given to Seiko's range of watches designed for scuba and professional diving. In particular, Seiko made these watches with saturation diving or greater depth diving in mind. All of the watches in the Seiko Tuna range are characterized by protective screwed-on shrouds that have earned them the nickname of “Tuna”.

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Seiko Prospex Professional 300M Tuna Ref. SBBN045 / S23629J1 |
The Seiko Tuna collection boasts of many firsts. The collection was the first to feature a titanium/stainless steel shroud, a monocoque case, an L-shaped gasket, and a vented rubber strap. Primarily built for functionality, the Seiko Tuna watches can withstand great depths as tools for professional divers.
Built in 1975, the first Seiko Tuna watch was created in response to a letter the company received in 1968. A saturation diver from Kure City in the Hiroshima, Japan sent a complaint regarding Seiko divers watches, which the company had been making since 1965. These pre-Tuna models were not robust to impact and could not withstand exposure to deep underwater pressure for prolonged periods.
Seiko engineers took on the challenge to create the “ultimate professional diver’s watch. These engineers, led by Ikuo Tokunaga, decided to develop the new Seiko Tuna watches for saturation diving from the start. Tokunaga and his team began development in 1968 and released the first Seiko Tuna watch seven years later with more than 20 patents.

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Seiko's iconic high tech quartz movement, 7C46
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Today, the SBBN045 shares the identical case profile of both previous iterations: the SBBN031 and 033, while upon taking a closer look, aesthetically they're quite different.
The Prospex Professional 300M Tuna Ref. SBBN045 is powered by Seiko's iconic high tech quartz movement, 7C46. The 7 jeweled movement with extremely hi-torque tolerances and high efficiency enables the gears and pinions to move and turn the hands in perfect sync to the energy-pulse, with much less kinetic effort via the electronic step motors that power them. Thus making for a highly accurate and efficient full size quartz machine to perform strongly with much less resistance resulting in longer battery life.
The 47.7mm stainless steel case might sound intimidating at first glance. But because of the "lug-less" design, the case is only 48mm lugs to lugs. That means this "Tuna" sits so comfortably on the wrist. In fact we think it fits more like a conventional 42mm watch with lugs. The stainless steel case and shroud is fine satin brushed for a up-market feel. We will let the pictures convince you.

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Stainless steel shroud with super hard coating
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The distinctive domed crystal and dial's hands are what set’s it apart from its precursors. The curved crystal only to be found on the 300m Tunas, is now being upgraded from the Hardlex mineral crystal to a solid sapphire one. Respectfully, right underneath Seiko has brought back the brushed silver handset that was found on the original 1975 Tuna Ref. 6159-7010, replacing the “Prospex” hands that was found on the SBBN031/033. Both the hour markers and hands are treated with Seiko's Lumibrite for awesome low light visibility. Dual-curved Hardlex for added toughness.
Furthermore, gone are the “Marinemaster” text at the bottom, swapping out to the “X” shaped Prospex logo, adhering this Tuna within the professional sports watch category, alongside with the other elites, like the SBDX023 and the SBDB027 LX.
The final touch to complete the sporty professional look of this Tuna is its black silicone strap which has an accordion design. This waterproof strap also flaunts excellent durability and resistance to wear and tear. Admire the seamless design of this rubber strap that tapers down to its tips, preventing the timepiece from being overly bulky and subtly elevating its Tuna case shape.
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Seiko's Lumibrite needs no introduction |
Overall, the latest Tuna 300m is a premium upgraded addition to the Prospex collection. This Seiko timepiece has won me over with its vintage design and superior tuna-can case, I can't get my hands off it! This exquisite watch presents a compelling set of specs and as quantities aren't limited, it is less difficult to get in on the action.