This is a 40xxxx-serial, Mark IV 1665 double red seadweller from the first owner’s family.
The watch appears to be unpolished. It was purchased in 1976, with the owner’s details stated on the punched paper.
The watch also comes with a service receipt from Rolex London in 1977, when it was sent for a water pressure test.
Such documentation is rarely seen with a vintage seadweller, and makes this watch highly desirable.