Rolex introduced the Submariner 5508 in 1958, preceded by about half a dozen other models. All of these models were released in just five years since the introduction of the Rolex Submariner, which would be hard to imagine today as we are used to Rolex producing the same model for at least a decade. The company experimented with the design of the Submariner in the 1950s, trying to strike the perfect balance between legibility, durability and performance to produce the ultimate dive watch. This was not to create the world's most luxurious sports replica watches but rather in the pursuit of making the most reliable tool watch for underwater divers. Those early Submariner models from the 1950s varied in terms of water resistance, dial details, and crown size. Prior to the 5508, there were incongruities in the dials of the Submariner. Some dials had hour markers - similar to those of contemporary Submariners - while others had Explorer-style dials with 3, 6, and 9 indicators. Many collectors divide these vintage 1950s submarines into "large crown" and "small crown" groups. The replica Rolex Submariner ref. 5508 is a "small crown" variety, featuring a 6 mm crown (for comparison, the "large crown" submarines include an 8 mm crown) and a slightly slimmer case. Rolex produced Submariner 5508 until 1962, and its production cycle overlapped with other models such as Submariner 6538, 5510, and 5512. Another key adjustment that came along with the 5508 was the change of the Rolex Submariner reference number to the 55xx string, which lasted into the 1990s.