ROLEX.A MEN'S STAINLESS STEEL AUTOMATIC WRISTWATCH "DOUBLE RED, MARK IV"Model: Sea-Dweller (Mark 4 dial)Date: 1978Case reference: 1665Movement: Signed, 26-Jewels, Cal. 1530, No. D420954Dial: Signed, black, applied luminous hour markers, white outer minute division, silvered Mercedes hands with luminous insert, centre seconds hand, date aperture at the 3 o'clock position, centre red "Sea-Dweller Submariner 2000"Case: Signed, brushed and polished stainless steel Submariner Case, bi-directional bezel with black bezel insert, screw down crown, screw down back, back engraving "Oyster Gass Escape Valve Rolex Patented", first generation Gass Valve on the left side of the case at the 9 o'clock position, No. 5017329Strap: Generic brown leather strapCase size: 38mm, bezel 39mmDuring the 1960's, the divers started working at deeper atmospheres for prolonged periods of time. Due to the change in their working conditions, they were having problems when they were using the Rolex Submariner 5513. The deeper the divers went and the longer they spent under water, the more gasses they would absorb. This meant that their bodies required more timeto safelyrelease those gasses before they could reach the surface.To save time during such process, the divers started using the saturationtechnique with a Helium-Oxygen mix instead of plain air, whichis made of nitrogen (inducing narcosis) and oxygen. Helium is released by the body faster, requiring thus less time for them to decompress. As a result, the divers were able to return to the surface in pressurised chambers and stay inside them until it was time to dive again. In this way, they just had to decompress once, increasing the time they could spend working.During that time the divers were breathing the Helium-Oxygen mix in the pressurised chamber and the helium molecules started to penetrate the acrylic crystalof the watch. At the end of the work periodthe divers were brought back to atmospheric pressure faster and the pressure inside the watch pushed thecrystal out destroying the watch.Comexasked Rolex to find a solution to release the pressure inside the watch and in 1967, the first gas escape valve was patented.In 1967 the new Rolex Sea-Dwellermodel 1665 was fitted with thicker lenses, which enabled the watch to perform at a depth of 610 meters (2000 feet), aSubmariner case and a very high standing bezel. Later that year a thicker case was introduced, and on the back of the case 1665, you were able to read Patent Pending instead of Patented which is seen on later examples.The first Sea-Dwellers are described on the dial in red print as Submariner Sea Dweller 2000.This particular style was used just during the following 6 years, to be later replaced with an all-white print dial that carried only the Sea-Dweller.After that, all the Comex's saturation divers were issued with a 1665 case, white dial print Sea-Dweller which displayed the Comex logo on it instead of the word Sea-Dweller.The Comex's divers achievedmany world records until the 1990's when both companies finished their collaboration.Today the first 1665 Sea-Dwellers are highly sought after. The watch wasn't a big seller for Rolex during that periodand since Sea-Dweller were used by divers as working tools, few survive in good conditions.The same model and case reference watch was sold at Sotheby's, 24th September 2019, Lot 77 for £27,500