In the mid-1960s the French commercial-diving company COMEX (Compagnie Maritime d'Expertises) was pioneering saturation diving: divers worked for weeks at a time at depths of 200m or more, living in pressurised helium-rich habitats, decompressing slowly over days. Conventional dive watches failed. Helium atoms are small enough to slowly seep through case gaskets during pressurisation; on slow decompression, the trapped helium expanded faster than it could escape, popping crystals off cases. The Submariner was an early casualty. Rolex and Doxa independently solved the problem in 1967 by developing a helium escape valve, a one-way pressure-release valve in the side of the case that vents helium during decompression without compromising water resistance.
The first Sea-Dweller, ref. 1665, launched in 1967 for COMEX use and went into commercial production around 1971. It was rated to 610m / 2,000ft. The early dial featured the SEA-DWELLER and SUBMARINER 2000 text in red on the matte black dial; collectors call this the "Double Red Sea-Dweller" or DRSD (1967-77). After 1977 the dial wording moved to white only ("Single Red" is collector slang for transitional pieces; "Great White" for the all-white dial). The 1665 is a vintage cult reference, and well-preserved examples sell for USD 25,000-100,000+ depending on dial condition and provenance.
The ref. 16660 (1978-89, Cal. 3035 then 3035) introduced sapphire crystal and pushed water resistance to 1,220m / 4,000ft. The ref. 16600 (1989-2008, Cal. 3135) is the longest-running Sea-Dweller, a 21-year production run that overlapped with the launch of the Sea-Dweller Deepsea ref. 116660 in 2008, a 44mm 3,900m monster with a Ringlock case construction. The standard Sea-Dweller line was discontinued briefly between 2008 and 2014, then revived as the ref. 116600 (2014-17), and replaced by the 43mm ref. 126600 in 2017, which added a Cyclops magnifier (a first for the Sea-Dweller, which had always omitted it for clean dial geometry under high pressure).
The current Sea-Dweller ref. 126600 (43mm steel) and 126603 (two-tone steel + 18k yellow gold, the first non-steel Sea-Dweller in catalogue production) carry the Cal. 3235, a 70-hour power reserve, and 1,220m water resistance. The Deepsea has continued to evolve in parallel with the ref. 136660 (2022, 44mm titanium-and-steel Ringlock). The Sea-Dweller remains a working tool watch, owned by serious commercial and recreational divers, and never quite as fashion-forward as the Submariner; this is the point. James Cameron wore one to the Mariana Trench (technically the Deepsea Challenge prototype, but the lineage runs through the Sea-Dweller).
