1960's Wittnauer Super Compressor (Ref. 8007)

The Super Compressor case was developed by Ervin Piquerez S.A. (EPSA) in the late 1950s with production lasting into the 1970s. The term "Super Compressor" comes from a Patented design that Ervin Piquerez S.A. (EPSA) created in which the case sealing method actually became more watertight with increased pressure as a result of increasing depth. The design is complex yet simple in that the deeper in-depth that the watch when the more watertight the watch would become as a result. The increased pressure by design would allow the case-back to press against the O-ring gasket within the mid-case again increasing water resistance. Super compressors leverage two crowns, one that operates the winding and setting of the watch and one that operates an inner rotating bezel ring which is also a unique design feature specific to super compressors that allows for greater security of setting the inner timing bezel inside of the watch instead of externally whereas if the bezel was located externally it could be bumped out of position rendering an accurate measurement of elapsed time. 

Brands that utilized the super compressor cases included Longines, Hamilton, Universal Genéve, and Enicar. The Super Compressor cases came in two sizes: 42mm, as seen in vintage Longines Skin Divers, and 36mm, as seen in watches like this Wittnauer 8007.