Ref 2555 is an uncommon one on the market. The one-piece case, initially produced in 1954, features a water-resistant screw-down case back made by master Antoine Gerlach (identifiable by the key-shaped punch No. 4), which is perhaps the most interesting feature of this particular reference. Successor to the Calatrava ref 96, the thick, flat coin bezel is certainly a familiar feature. The special feature in this case lies in the dial; in fact, it can be seen that the color is black, a much sought-after feature on Pateks of this era, and it also bears applied Breguet numerals.Accompanied with an excerpt from the Patek Philippe archives confirming the production of this timepiece in 1956 and subsequent sale in 1957, this is a great opportunity for vintage Calatrave lovers to acquire one of the earliest “Etanche” references.