Sea-Dweller 16600 Tritium

The Sea-Dweller was developed in the late 1960s in partnership with COMEX, the French deep-sea diving company, for saturation divers who spent extended periods in hyperbaric chambers breathing helium-oxygen mixtures. The helium escape valve — a Rolex patent that allows helium molecules to exit the case during decompression without blowing off the crystal — was the Sea-Dweller's defining innovation and the feature that separates it from the Submariner. Rated to 1,220 metres (4,000 feet) in its current form, the Sea-Dweller has always been the Submariner's more capable, less glamorous sibling — a watch designed for professionals who needed more than 300 metres of water resistance and weren't concerned with whether it had a Cyclops lens.

Introduced in 1988, the Sea-Dweller 16600 is the heavy-duty brother of the Submariner 16610 of the same era. Compared to the Submariner, its case -now fitted with a helium escape valve- is slightly thicker. The glass does not feature the cyclops. The 16600 was replaced by the Deepsea 116660 in 2008. The watch pictured has a dial with Tritium indexes as used up to 1998.