In 1971, Rolex released the Explorer II, reference 1655. This model was aimed at speleologists, and produced as a 'tool' watch, not a luxury watch. This is consistent with Rolex's roots, as the company first made a name for itself by producing high-end watches that were seen more as items of necessity than luxury accessories. The Rolex 1655 was only offered in stainless steel, and did not offer gold or two-tone variations.
As it stands today, the Rolex Explorer II, reference 1655 is somewhat of an oddball in Rolex's history. It was made explicitly for cave explorers, yet promoted by actors and professional athletes. Its sales were disappointing while in production, however it is now one of the more popular and rare vintage Rolex references. Even the watch's face and brightly colored, 24-hour hand, which were previously criticized, are now the defining characteristics that give it such value. Since nearly every Rolex is a classic, even when they miss, they hit the mark… it just may take a few decades to catch on.