The Rolex watch introduced in 1967 as the first commercially available wristwatch designed for saturation diving was the Sea-Dweller.
Professional divers working in saturation habitats faced a problem during decompression: helium atoms could enter a watch during long periods in a helium-rich environment. When the diver returned to normal pressure, the trapped gas could force the crystal off the case.
Rolex developed the helium escape valve to release that internal pressure. The Sea-Dweller combined the valve with a robust Oyster case and greater water resistance than the Submariner. Early examples were produced for professional diving operations before the model became commercially available.
The Sea-Dweller is often confused with the later Deepsea. Deepsea is a more extreme Rolex dive-watch line with substantially greater rated depth; Sea-Dweller identifies the earlier saturation-diving design.