Swiss lever for the U.S. Army Corps of Engineers Circa 1918

Silver open faced lever chronograph by Vacheron & Constantin
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A fine and interesting Swiss silver open faced chronograph keyless lever pocket watch made for the U.S. Army Corps of Engineers, circa 1918. Chrono 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, co axial chronograph button on the winding crown. Hinged silver cuvette. White enamel dial with bold Arabic numerals, outer minute and 1/5th seconds chronograph scales, Arabic five second numerals, subsidiary seconds, partially replaced black spade and lozenge hands. Plain case. Dial, case, cuvette and movement signed, case numbered.
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Diameter: 52 mm
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Signed: Corps of Engineers U.S.A. Vacheron & Constantin Genève