Introduced in 1966/67, reference 1680 was the company's first Submariner with date, also featuring a "Trip Lock" crown as well as crown guards. The bezel has minute divisions for the first fifteen minutes and shows a silver triangle at the 60 unit.
The watch on offer here is a fine example of a reference 1680 MKI with nice ivory-tone numerals and hands, displaying a flawless dial.
Reference 1680 is prominently described and illustrated in Rolex Submariner Story by Franca & Guido Mondani and Lele Ravagnani, pp. 90-103.