Rolex, Sea-Dweller, "Double Red Mark IV", ca 1975.

Rolex 1665 is the original reference of the Rolex Sea-Dweller. When the model was introduced, it was the quintessential diver's watch, enabling divers to use the watch at greater depths thanks to a specially developed helium valve. During the first production years of the Rolex Sea-Dweller, the words "Sea-Dweller" and "Submariner 2000" were written in red on the dial, hence these models have been nicknamed "Double Red" and are sought after by collectors around the world. The dial is a correct Mark IV with "Closed 6". The case back is correctly marked "Rolex Patent" and has the serial number engraved.