The Sea-Dweller ref. 1665 was the firms first ever wristwatch to feature a helium gas escape valve to release pressure in a single way during deep explorations at the sea to conquer larger depths. In the late 1970’s, Rolex stopped its production for the Double Red Sea-Dweller which featured two lines of text in red on the dial and replaced it with the “Great White” dial, which no longer uses red lines of texts on the dial. The present example is fitted with a MK I dial, witnessed by the perfect alignment of the first two lines of texts on the bottom of the dial as well as featuring an “open 6”. The MK I dials were produced amongst the 5.18m to 6.2m serial, the present example bearing a 5.2m case fits perfectly within its production period and dates back to 1977. Boasting a strong case, the dial features luminous material that have aged evenly with an attractive pale yellow patina. An attractive example with beautiful vintage charisma, the bezel insert has furthermore faded into a gun-metal colour with grey blue hues that contrast nicely against its matte black dial.