The Rolex Sea-Dweller was introduced in 1967.
Rolex developed the Sea-Dweller for professional saturation divers who worked at depths beyond the practical limits of the Submariner. The early model was rated to 610 metres and was designed around the pressure challenges of prolonged underwater work and decompression.
Its defining innovation was a helium escape valve. Divers living in pressurized habitats could breathe a helium-rich mixture, allowing tiny helium atoms to enter a watch case. During decompression, trapped gas could force the crystal off; the valve allowed helium to escape while preserving water resistance.
There is an important timeline distinction. The Sea-Dweller was developed and introduced as a model in 1967, but the first version available to the general public appeared in 1971. Early 1967 examples also lacked the helium valve, which Rolex patented later. That distinction explains why some histories mention both 1967 and 1971, but 1967 is the standard answer to the introduction-year question.