THE ROLEX SEA-DELLER, introduced in 1971, is a heavier-duty version of the Submariner in steel, with a thicker case and crystal. The Sea-Dweller incorporates a helium escape valve which allows helium and other gases to escape, enabling the watch to withstand decompression. The Sea-Dweller (model ref: – 16600) is guaranteed waterproof to 1220 m/4000 ft. The Sea-Dweller was superseded by the Deep Sea Sea-Dweller in late 2008 with the last few 16600 Sea-Dwellers produced running into the V-series (late 2008).