The celebrated Sea-Dweller reference 1665 launched in 1967 was the first wristwatch designed for use in saturation diving, fitted with a Rolex patent valve in the band and guaranteed waterproof to 610 meters depth. The valve was first developed on the Submariner model and allows helium and other gases to escape, enabling the watch to stand compression.
The present watch is from the second, so-called "Mark II" or "Mk 2" series of the "double red" Sea-Dweller, in production between around 1967-1970 and distinguished by the printing on its dial.
The "double red" designation is crisp and bright red and different in size; the second line, "SUBMARINER 2000", is smaller than the first line "SEA-DWELLER". The Rolex crown has a rather indistinct or smudged appearance, the spikes are slightly distorted and the small oval to the base is hardly visible.
Another particularity of the "Mark II" dial is its color, changing over the year from black to a chocolate-brown, such as the present watch.