Interesting Swiss silver pocket watch with chronograph Circa 1918

Silver open faced lever pocket watch
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A fine and interesting Swiss, keyless, silver pocket watch with a chronograph, circa 1918. Corps of Engineers USA by Vacheron & Constantin, Genève. Made for the U.S. Army Corps of Engineers. A polished case, hinged silver cuvette engraved: To a damn good boy on his 21st birthday, Nov. 26th 1939, dad. White enamel dial with bold Arabic numerals, outer 5-minute/seconds Arabic and 1/5th seconds chronograph scales, sunk subsidiary seconds dial. Blued steel skeleton hands. A rhodium-plated movement, partial oeil-de-perdrix decoration, 20 jewels, straight-line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring, swan-neck micrometre regulator, chronograph button on the winding crown. Dial, case and movement signed.
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Diameter: 52 mm
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Signed: Vacheron & Constantin  Genève