Interesting Swiss silver military watch with chronograph Circa 1918

Silver keyless lever military watch
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An interesting Swiss, silver keyless pocket watch with a chronograph, circa 1918. Made for the U.S. Army Corps of Engineers. A polished case, hinged silver cuvette. White enamel dial with bold upright Arabic numerals, outer Arabic minute and chronograph ring and subsidiary seconds. Blued steel skeleton hands. A frosted gilt brass movement, 20 jewels, straight-line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring, swan-neck micrometre regulator, chronograph with visible work, and the 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