Interesting Swiss silver chronograph lever military watch Circa 1918

Silver open faced military chronograph by Vacheron & Constantin
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A fine and interesting Swiss silver open faced chronograph keyless lever military pocket watch, circa 1918. Made for the U.S. Army Corps of Engineers, issue No. 2566 to J.B. Barnes. Matte gilt movement, 20 jewels, straight-line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring, swan-neck micrometre regulator, visible chronograph work, co axial chronograph button on the winding crown. Silver hinged cuvette. White enamel dial with bold Arabic numerals, outer minute track and fifths of a second chronograph divisions, subsidiary seconds and original dial luminous steel skeleton hands. Solid, polished case on the back with Corps of Engineers inscription. Dial, case, cuvette and movement signed, case and movement numbered.
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Diameter: 52 mm
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Signed: Corps of Engineers U.S.A. Vacheron & Constantin Genève
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This watch was produced especially for the U.S. Army Corps of Engineers, founded in 1775 by the Continental Congress. The Corps requested a watch for field use, with a silver case, a white dial with luminous Arabic numerals and hands, and a simple chronograph movement without counter.