The Rolex Sea-Dweller and its extreme-depth successor, the Deepsea, represent the outer limits of the brand's dive watch engineering. The original Sea-Dweller, introduced in 1967 in partnership with the professional diving company COMEX, addressed a critical limitation of the Submariner: helium molecules that penetrated dive suit seals during saturation diving would expand during decompression and destroy watch crystals. Rolex's solution was the patented Helium Escape Valve, a feature that has defined the Sea-Dweller ever since. Early references including the 1665 "Great White" are now serious collector pieces. The modern ref. 116600, introduced in 2014 with the Rolex text reintroduced to the dial, caused a collector frenzy. The Deepsea, reference 116660 and its successor 126660, is rated to an astonishing 3,900 meters, employing a Ringlock System and sapphire crystal of extraordinary thickness. The Sea-Dweller 50th Anniversary ref. 126600 with its red text is among the most discussed recent releases. Pre-owned examples of both lines offer deep technical heritage. DeMesy & Co. in Dallas has authenticated pre-owned Sea-Dweller and Deepsea references since 1987.