The ref. 1680 was the first in Submariner’s history to feature a date and, to ease the reading, the “cyclops” lens on the plexy, allowing for a 2.5x magnification. The 1680 is labeled as waterproof up to 200 meters.
The caliber inside is a 1575, who’s actually a 1570 with a date disc.
Fun fact: you’ll never find a movement labeled as “1575” because, regarding of the actual version of the movement, they were both inscribed as “1570”.
From 1971, the movement was equipped with “hacking seconds”: when you want to set your Submariner’s time, the seconds hand stops allowing you for a more precise setting. The date mechanism is “Quick switch” and “Slow set”.
This 1680 is a “WHITE ”feet first MK3. This is the dial type that Rolex sold between 1977 and 1979, with all white graphics.