Extremely fine French platinum keyless dress watch Circa 1940

Platinum open faced lever pocket watch
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An extremely fine and rare French, extra thin, keyless platinum dress watch, circa 1940. A solid, brushed case, knife edge, curved bezel, oval pendant. Matte and engine-turned moire silver dial with painted radial Arabic numerals, outer minute track. Blued steel Breguet hands. A frosted gilt movement, 18 jewels, straight-line lever escapement, cut bimetallic compensation balance, blued steel flat balance spring, index regulator. Dial and case signed, case stamped with the Cartier inventory number.
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Diameter: 53 mm
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Thickness: 4 mm
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Signed: Cartier  Paris
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The dial is slightly scratched.
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Cartier sourced their Couteau watches from several suppliers. These included, as of 1935, Jaeger who had just invented a movement of 7.75 douzièmes, and Vacheron & Constantin, who from 1940 utilized a movement which was seven douzièmes or 1.31 mm thick. This allowed them to produce incredibly thin watches, as is the case with the present watch. This watch, less than 4 mm. thick, is one of the thinnest mechanical watches ever produced. It is also of an unusually large diameter for its type.