Barth tells of how he and his fellow crew members in an interview conducted by Jason Heaton back several years ago, while undergoing decompression in a decompression chamber, would hear a quick “pop” sometimes only to find that the crystal of someone’s fake watch – Submariners, Blancpain’s, and Tudors, mostly – had come off. The basic problem was the helium in the breathing gasses used in SEALAB. Helium forms very small molecules, which can over time penetrate the seals of a dive watch and build up in the case. Divers would spend a few days in a decompression chamber, where air pressure would gradually be lowered from that at working depth, to air pressure at sea level. The helium would not be able to leak back out of the watch case quickly enough and the result was increasingly greater pressure inside the watch case – often, enough to pop the crystal off. It was the SEALAB missions that first called for a helium escape valve, which was introduced within the fake Rolex range on the Sea-Dweller and remains a staple of this model to this day. 
There are a few early Sea-Dwellers that have only one line of red text on the dial. These “Single Red” Sea-Dwellers are exceedingly rare, feature a depth range of 500m instead of 600m, and often times do not have a helium escape valve. These are prototypes and generally fetch hundreds of thousands of dollars at auction, such as this one did in 2013.
The Rolex Sea-Dweller replica watch was introduced in 1967 as Rolex’s biggest, badest, most capable dive watch. It was water-resistant up to 610 meters and featured two lines of red text reading “Sea-Dweller / Submariner 2000”. The crown was a Trip-Lock; the watch featured a date (useful to saturation divers who could spend days in a decompression chamber) and it was the first time a Rolex diver would feature the complication, predating the 1680 Rolex Submariner ever so briefly. 
The bracelet had an extension clasp that allowed the owner to quickly open up the bracelet to allow it to fit on the outside of a diving suit. What’s more, the crystal was domed and cyclops-less. This is how the replica Sea-Dweller watch was born and how it remained for some time and over the years we would see continual improvements to water-resistant engineering in Rolex’s most professional line. Of course, we know it, actually after the Rolex replica killed the Sea-Dweller.
Captain Bob Barth’s Best fake Rolex Submariner Model
