In the late 1960s, Rolex worked in collaboration with the deep sea diving company Compagnie Maritime d’Expertise, or COMEX, to develop the helium escape valve – and the basis for the Sea-Dweller. While working inside pressure-controlled diving chambers, the tiny helium atoms of the air mixture that COMEX divers breathed would penetrate the case and get trapped inside, causing their watches to burst upon resurfacing. The helium escape valve was a brilliantly simple solution that allowed the helium to easily escape. Rolex produced a batch of approximately 300 reference 1665 Sea-Dwellers for COMEX between 1977 to 1981. Their dials featured the COMEX logo printed in black inside a white box. Their casebacks were engraved with a prominent issue number and inside, the full serial number was engraved. The present example includes its original COMEX dial noted by the 600 m depth rating. The dial’s luminous hour markers have gracefully aged to a pleasing ivory-colored tone, identically matching the color of the original luminous hands.