The Rolex Submariner reference 1680 was introduced in the late 1960's. Its arguable but most say the 1680 was introduced in 1969 and was produced until 1978 when it was replaced by the reference 16800. 

The 1680 was the first submariner to feature a date function via the loved (or dreaded) cyclops in the Plexi-glass crystal. To accommodate this Rolex modified the 1570 movement to include a date function, becoming the 1575. 

What makes this watch so much fun for collectors are the variety of dial variations available. Altogether, there are 7, designated by collectors as Mark I-VIII (Mark II/III are usually coupled as one type).  

The earliest versions of the 1680 featured the word "SUBMARINER" in Red. These are the most desirable versions of the 1680. 

Photo courtesy of Bob's Watches

The 1680 is a great starter watch for those looking for a vintage submariner to start with. Prices are on the rise, however there are plenty of dial variations available for below the $10k mark.