1977 Rolex Great White Sea-Dweller (Ref. 1665) "Rail" Dial

In the early 1960s deep-sea diving, particularly mixed gas diving, was advancing at a rapid rate. The Rolex Submariner was the quintessential diver at the time, born out of the late 1950s, which set the design standard for most all dive watches that came after. The Rolex Sea-Dweller was first introduced in 1967, through the collaboration with COMEX, a French deep-sea diving company. Comex is sometimes referred to as the NASA of the deep seas and was the foremost pioneer in mixed gas saturation diving.

In typical Rolex fashion, meaning form following function. Most of the Sea-Dweller design was born out of the need to comply with the commercial ISO 6425 diving standard, which defines test standards and features for watches suitable for diving with underwater breathing apparatus in depths of 100 m (330 ft) or more. Rolex developed a rather simple and practical mechanism to solve this issue by developing a helium escape valve on the side of the case that allowed the helium particles to escape while still maintaining an ISO 6425 diving standard and water resistance rating.

While the first few prototype ref. 1665 Sea-Dweller models featured a single red line of text, the typeface design was quickly altered to feature two lines of red text, these models are most commonly referred to as "double red Sea-Dwellers". However, the Rolex Sea-Dweller ref. 1665 the dial configuration was updated in 1977. This new dial configuration is often named the "Great White" as the two lines of red text were removed and replaced with a single, but very bold line of white text that simply reads "Sea-Dweller"

Amongst the "Great White" dial variations within the production run of the ref. 1665, the "rail" dial variation receives the praises of collectors more than any other dial. This extremely uncommon dial features the same well-organized typeface that is seen in the issued COMEX watches of the same era. Interestingly, this dial was only produced for 2-years by the Stern Company for both civilian and professional use, as a select few were set aside specifically for COMEX printing while the rest made it into general production, though at a very limited number.

The Sea-Dweller was undoubtedly the most advanced among the diving watches of its time, and the model remains at the forefront of advancement today.