The Seiko Prospex Mini Tuna SUT403P1 is part of the iconic and recognised watch case designs that feature the ‘tuna-can’ style. Introduced in 1975 to mainly combat the issue of helium gas penetrating the case, it has symbolised their dive watches ever since and has a cult following and a cult dislike.

Whichever side of the fence you sit on it still dominates many of Seiko’s collection of watches today. One of those collections which lend itself perfectly to the tuna style case is the ‘street series’ which debuted a couple of years ago.

As with a lot of watches I like, they are too big for my wrist. I’ve always loved the ‘tuna’ style case but struggled with the size. Now you can get one of these street series watches in either 44m or 38mm diameters. The Seiko Prospex Mini Tuna SUT403P1 comes in a green and champagne or a deep blue and champagne colourway. These are distinctive watches utilising a Solar movement and 200 metres of water resistance. So very capable tool watches even if the marketing isn’t aimed at this.

I pined for the deep blue and champagne colourway in 38mm and was very impressed by the many details and unique features Seiko squeezed into this midsize watch. You have bold baton style applied indices which have a faint trace of vintage patina on the outer edge of the lume plots, which you don’t notice initially. A lumed Baton style handset to match these to give a very clean, modern feeling and legible dial.

The second hand on the Seiko Prospex Mini Tuna SUT403P1 is particularly quirky with an arrowhead and black tail harking back to Seiko dive watches of old. The blue dial has a little trick up its sleeve with a subtle sunburst effect which is always nice to catch a glimpse of, as with so many other dive watches you just get a plain coloured dial, and a thin rehaute with minute track gives a subtle appearance of depth.

The dial text is kept to a minimum with the familiar ‘prospex’ logo giving this watch a hint of its intended functional purpose. And finally, an ever so slightly domed hardlex crystal, which you hardly notice. The standout feature for me is the bezel, overflowing with gorgeous details, like a lume plot at 12 o’clock, engraved minute markers and numerals at 3, 6 and 9. All on top of concentric grooved ridges giving a matt appearance, but throwing that off ever so slightly in varying light conditions.

Looking at the watch as a whole, you have a lot of textures and surfaces at play adding to the wrist presence. Polished lugs, brushed outer case with polished cutout sections for bezel operation. Polished hex-screws and the standard crown at 4 o’clock. You could argue this is all too much and I honestly would’ve preferred a complete matt/brushed finish all over. But it works in the context of the collection it is intended for.

Overall, with a lug to lug of only 41mm and case depth of just 11mm this watch wears small, even smaller than the stated dimensions as the dial aperture is compromised by the tuna case design and unidirectional 120 click bezel. It takes some getting used to, but legibility and bezel/crown operation are not compromised.

The Seiko Prospex Mini Tuna SUT403P11 comes with the classic Seiko wave engraved case back which is such a lovely feature and drilled lugs so you can experiment with the look of this watch as it works very well on a rubber strap, bracelet or a nato. Overall finishing is typically Seiko, very good for the price.

There’s no date on this model, but the 44mm variant has that at the 4 o’clock position.

Daily wearing is a breeze. It’s so slim and hugs the smallest of wrists with ease. The accompanying strap is supple and not overly long but the buckle and metal keeper are of basic construction and nothing special.
Overall, it’s nice to see Seiko continue with this recognisable case design and give it a fresh rethink outside the dive watch aesthetic it’s so famous for and with a smaller case size to widen that appeal.