The Reference 1680 was introduced 10 years after the Submariner 5512 came to market and 16 years after the Submariner made its debut and was the eventual successor to one of Rolex’s longest serially produced references. The 1680 brought a major innovation to the Submariner line, with the addition of a date window underneath the "Cyclops" date magnifier. Also the Ref. 1680 is labeled as waterproof up to 200 meters and has a chronometer status.
The calibre inside is the 1570 with a date disc (already featured in the Datejust and GMT-Master). 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".