Rolex Sea-Dweller 16660

In 1967, Rolex launched the Sea-Dweller for saturation divers—professionals living in pressurised underwater habitats for weeks, breathing helium-oxygen mixtures at depth. When they decompressed, helium molecules trapped inside standard dive watches expanded and blew crystals off cases. Rolex's solution: a helium escape valve. Patent 3,203,252. A one-way valve allowing helium to exit without compromising water resistance. The Sea-Dweller became the only watch commercial divers actually needed.

This 16660—nicknamed "Triple Six" by collectors—represents the reference's final production years. Launched in 1978, it remained in production until 1988, though 1989-dated examples exist from remaining stock. Forty millimetres. Unidirectional aluminium bezel. Glossy black dial with white gold surrounds on the hour markers. The text reads "SEA-DWELLER" in red, "SUBMARINER 4000" below it. Twelve hundred metres depth rating—4,000 feet. Cyclops magnification over the date window at 3 o'clock. Sapphire crystal.

Inside: Calibre 3035, Rolex's high-beat automatic movement introduced in 1977. Twenty-seven jewels, 28,800 vibrations per hour, 42-hour power reserve. COSC-certified chronometer. The 3035 was Rolex's workhorse through the 1980s—reliable, serviceable, proven. Hacking seconds, quickset date, Chronergy escapement. This movement powered Submariners, GMT-Masters, Explorers. Utterly dependable.

The helium escape valve sits at 9 o'clock—a small protrusion with Rolex's patented spring-loaded mechanism. During saturation diving, helium molecules (smaller than water molecules) permeate the case. During decompression, internal pressure builds. At roughly 3-5 bar differential, the valve automatically releases helium. Simple, mechanical, foolproof. No diver intervention required.

"Well loved" means this watch worked for a living. The aluminium bezel insert shows fade—once jet black, now grey or charcoal depending on light. The pearl at 12 o'clock might be aged or replaced. The case lugs show polishing from decades of service intervals. Bracelet stretch is inevitable after 35 years. The dial, if original, displays warm patina—cream-coloured lume rather than bright white. These aren't flaws. They're provenance.

The 16660 matters because it's the last Sea-Dweller before Rolex modernised the line. The next reference, 16600, arrived in 1988 with upgraded movement (Calibre 3135) but looked nearly identical. Then in 2008, Rolex expanded the case to 43mm, added ceramic bezel, discontinued the red "SEA-DWELLER" text. The Triple Six represents old-school tool watch design—built for purpose, sized appropriately, worn until it couldn't be worn anymore.

Full set means box, papers, warranty booklet, hang tags—documentation proving this watch left an authorised dealer in 1989. For vintage Rolex, provenance matters. The papers confirm authenticity, date of sale, original configuration. Well-loved condition with full documentation is preferable to pristine condition without it. This watch has history. Wear it accordingly.