From 1965 to 1968, Seiko produced its very first dive watches. At that point, saturation diving (divers working at depths for extended periods), was an upcoming new concept. It necessitated dive watch design to be altered to prevent crystals from popping off when the watches filled with helium.
In 1975 Seiko produced an enormous 51mm dive watch with a protective shroud, 600m depth-rated, the first Seiko Tuna (ref. 6159-7010), as the result of more than 20 patents and world's firsts with ground-breaking features, to become industry-standard.
The ceramic shroud around the case, secured with three rivets offered extra protection to the bezel, particularly during deep-sea diving, prevented accidental impacts or jostling that could disrupt its crucial timing function underwater under extreme conditions. This shroud also gave the watch its nickname ‘Tuna’ due to its resemblance to a can of tuna encasing the watch case.
Seiko Tunas have since come a long way featuring a variety of high-end calibres in automatic, quartz and solar movements. The case sizes have shrunk from 51mm to 43.2mm.
The Steeldive homage’s overall dimensions and appearance (dial, indices, bezel font and pointers), primarily pay homage to the Seiko 7549-7010 Tuna Can, a.k.a. Baby Tuna, with a rated water resistance of 300m. The text on dial at 6 o'clock, is inspired by Seiko Prospex SBBN031's three-line nomenclature ('MARINEMASTER' 'PROFESSIONAL' '300m'), here 'MARINEENGINEER' 'AUTOMATIC' '300m' instead. I believe this watch is depth tested at Steeldive’s lab for the claimed water resistance depth.
While the original featured a Seiko 5-jewel, 7549-calibre quartz movement, a day/date window at 3 o'clock, tritium pointers, a bi-directional bezel, aluminium protective shroud and mineral crystal, the first homage (SD1975) is powered by Seiko's NH35 automatic movement featuring a date window (no day) at 3 o'clock, a 120-click unidirectional ceramic bezel, 316L stainless steel protective shroud and a sapphire crystal with AR coating. Case dimensions vary marginally by 0.5 to 1mm. Both watches feature a 22mm lug width and a slightly domed crystal.
The SD1975V varies from its sibling - date window at 4 o'clock (like the Seiko Prospex Solar Tuna Stainless Steel Diver SNE497P1), BGW9 blue lume (bezel graduation 21 to 59 minutes), Swiss C3 green (indices, pointers), and graduation from 0 to 20 minutes on the bezel with Swiss orange super luminous.
The screw-down crown and case back both with polished and brushed surfaces, bear the Steeldive logo - the case back announces the watch's chief characteristics around its etched logo.
Despite the 47mm dia. case, lug-to-lug measures just 44.5mm with recessed, downward lugs from the case appearing as tiny bumps beyond the shroud on its return sweeps. So those conspicuous gaps between your wrist and the watch case at the lugs are avoided.
The watch case is polished but the shroud is brushed. The bezel coin edge has brushing on the outer surfaces while the inners are polished. The ceramic insert of the SD1975V offers a distinct sportiness with dual-colour graduation.
The Tuna Can design shroud checks the movement of the bezel to small advancements in true design form. Bezel action is firm without back-play and perfectly aligns with the chapter ring.
The engineer-style, 5-link, solid, brushed finish bracelet with polished edges, is something to behold! The multi-links ply very well so the strap closely follows the contour of the wearer's wrist. It does not taper but boldly road-rolls its 22mm track all the way, complimenting the strength and durability that the case and shroud abundantly exude. The signed clasp is milled but the clasp lock could have been of a thicker gauge. The clasp has six micro-adjust points, ensuring fine adjustment to your wrist size, a must in the circumstances. The lugs are drilled and slots are provided at the spring-bars for easy accessibility.
With a NATO strap to match the dial, indices and bezel, my SD1975V is a beauty from the depths of the ocean with whom I am ready to take that deep dive!
The Steeldive homage checks all the boxes in my book - strong fundamentals (SS316L case/shroud & Seiko NH35 automatic), applied indices with long-lasting lume, finely finished pointers, a legible date window with lume surround, a precisely printed dial, firm bezel and a screw-down crown with smooth operation.
The watch dimensions (diameter 47mm, height - 14.4mm) and weight - 215 gms., make it impractical for daily wear. However, the 'Tuna' is an absolutely essential collectible, the design an integral part of dive watch history kept alive for half a century, and immortalized by homages from many micro-brands as also Seiko's Alba!