The story of the DOXA SUB 300T

by Brent Robillard

The Cousteau Connection

I have fond memories of watching Jacques-Yves Cousteau on the CBC when I was a kid. I grew up in a household of four boys in a town along a river, and most of our summers were spent at a nearby lake. We lived in the water. I could probably swim before I could walk.

Despite that fish-like childhood, deep water always made me uneasy. Maybe the film Jaws had something to do with it. Watching Cousteau through our grainy television set helped soften that fear. His underwater world felt calm and fascinating rather than threatening.

At the time I had no idea Cousteau had any connection to DOXA. I also had no idea what a dive watch was.

That discovery would come much later.

DOXA SUB 300T with diver gear — DOXA SUB 300T @calibre321

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In the beginning

Years down the road I fell into the familiar rabbit hole of watch enthusiasm and eventually became a recreational diver myself. Somewhere along that path I learned the story of the DOXA SUB series, and it immediately stood out.

In 1967 DOXA released the SUB 300, a dive watch developed with input from professional divers, including members of Cousteau’s team. The watch introduced several practical ideas that still define DOXA today.

The bright orange dial was the most obvious. DOXA tested colours underwater and concluded that orange remained visible longer than most other dial colours as depth increased. The watch also carried a distinctive bezel that combined elapsed dive time with no-decompression limits based on U.S. Navy dive tables. For divers, that meant fewer calculations and quicker decisions during a dive.

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The SUB 300 Conquistador

In 1968 DOXA followed up with the SUB 300T Conquistador. The new watch addressed a problem that had begun to appear in saturation diving. Divers living in pressurized environments discovered that helium molecules could enter a watch case during decompression. When pressure dropped, the trapped gas sometimes forced the crystal off the watch.

DOXA’s solution was straightforward. The SUB 300T introduced a helium release valve that allowed the gas to escape safely. It became the first publicly available dive watch equipped with this feature.

That was a significant development at the time.

DOXA SUB 300T on wrist and amid adventure gear, maps — More than just a desk diver @calibre321

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DOXA SUB 300T on wrist, highlighting legibility — A tribute to the Conquistador @calibre321

The contemporary SUB 300T

More than fifty years later, the modern SUB 300T still follows that blueprint.

The current version, introduced in 2019 as a tribute to the original Conquistador, keeps the familiar design while updating the construction. The case is made from 316L stainless steel and measures 42.5 mm across with a height of 13.65 mm. Water resistance is rated to 1,200 metres, which places it firmly in professional dive-watch territory.

A scratch-resistant sapphire crystal replaces the acrylic found on vintage models. The patented unidirectional bezel remains one of the defining elements of the watch. Its engraved scale still incorporates DOXA’s no-decompression dive calculator based on U.S. Navy tables.

Inside beats a Swiss ETA 2824-2 automatic movement running at 28,800 vibrations per hour with a power reserve of about 38 hours. The layout is straightforward: hours, minutes, central seconds, and a date. A screw-down crown, screw-down caseback, and helium release valve complete the technical package.

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Our review example arrived on DOXA’s stainless steel beads-of-rice bracelet with a folding clasp and ratcheting wetsuit extension. The bracelet is closely tied to DOXA’s identity and has been associated with the brand’s dive watches for decades. Frankly, I have a soft sport for this type of bracelet and own several other timepieces with this configuration. The watch is also available on an FKM rubber strap for those who prefer something lighter in the water.

A wristcheck with the DOXA SUB 300T — Now available in 8 colourways @calibre321

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I had the chance to handle pieces from the larger SUB 750T collection earlier this year, and I’ve always admired the vintage tool watch character of the SUB 300. The SUB 300T sits further along the professional spectrum. It is thicker, more robust, and clearly built with demanding conditions in mind.

That said, very few divers rely solely on mechanical watches anymore. Even when I dive recreationally, I double-wrist with a dive computer on my left and a mechanical watch on my right.

But that isn’t really the point.

A lumeshot of the DOXA SUB 300T — Super-LumiNova @calibre321

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A pocketshot of the DOXA SUB 300T with a clear view of the dual-purpose bezel — Surprisingly comfortable on wrist @calibre321

Final Thoughts

The SUB 300T reminds me of summer. It brings back memories of lakes, Cousteau documentaries, and those early impressions of the underwater world. As I write this, we are preparing for a mid-March storm front expected to bring twelve hours of freezing rain. A watch that calls to mind warm water and open skies is a welcome distraction.

On the wrist the SUB 300T wears better than its diameter might suggest. My wrist measures about 6¾ inches, yet the cushion case distributes its weight well. The relatively short lug-to-lug measurement helps, and the case shape keeps the watch balanced.

The bezel deserves special mention. Its sharp edge makes it easy to grip, and the action is firm and precise. It feels exactly like what it is: a dive watch designed to be used.

And despite the sapphire crystal, modern machining, and updated movement, the watch still feels remarkably close to the SUB 300T introduced in 1968. The dial remains simple. The hands are bold and easy to read. The bezel still carries dive tables.

Sometimes a design sticks around because it works.

The SUB 300T is one of those watches.

You know what they say, “If it ain’t broke…”