Sea-Dweller

The Sea-Dweller was designed for a kind of diving in which coming back up could be as troublesome for a watch as going down.

During saturation work, divers live in a pressurized habitat and breathe a gas mixture containing helium. Over time, helium can enter a watch case. When the pressure outside is reduced during decompression, the gas trapped inside may not escape quickly enough. It can damage the watch or force the crystal out.

Rolex introduced the Sea-Dweller in 1967 with an automatic helium escape valve. The valve lets excess internal pressure out while preserving the case's water resistance. It solves a different problem from the thick case and crystal that resist water pressure.

The original depth rating was 610 meters, increased to 1,220 meters in 1978. The family remained closely associated with professional diving, including Rolex's work with the French underwater engineering company Comex.

The Deepsea, introduced in 2008, extended the pressure-resistant construction much further. Its Ringlock system supports the thick sapphire crystal and case back around a strong internal ring, with a rating of 3,900 meters. The large case is the visible consequence of that construction.

The 43-millimeter Sea-Dweller 126600 and the 44-millimeter Deepsea generations therefore occupy different branches. The Sea-Dweller has a magnifying lens over its date and a 1,220-meter rating. The Deepsea has the more elaborate pressure structure, no date magnifier and a much thicker crystal.