During the 60s, commercial activities in the oceans and seas from professional organizations required long dives. So Rolex designed safety clocks for very deep immersion operations.

With an official depth of 4000 feet (1220 meters) for the Sea Dweller and 12800 feet (3900 meters) for the Sea Dweller Deepsea, these watches are capable of tackling the greatest depths of the planet.
Down there abysses are no longer blue, they're black. Like a Black Venom.