Rare Swiss sterling silver lever navigation watch Circa 1940

Sterling silver open faced pocket watch
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A rare Swiss sterling silver open faced navigation pilot observation watch with indirect center seconds made for the South American market by Longines Francillon S.A. in Geneva, circa 1940. Delivered to Panair do Brasil. The ½ plate movement with 21 jewels, a piston tooth lever escapement, stop device for the seconds, Glucydur screw balance and adjusted to temperature and five positions. Black enamel dial with an inner 24 hour track, an outer minute track with Arabic five minute numerals and spade hands. The plain case with a screw back. Dial marked GCT Swiss, movement numbered and signed Longines Watch Co. Swiss, the case back numbered and signed Panair Do Brasil S.A. L 49  and the inside case back numbered and signed cased and timed in U.S.A. by Longines, movement and case back with matching numbers.
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Diameter: 52 mm
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Weight: 106 g
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Signed: Longines Watch Co. Swiss
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Panair Do Brasil S.A. was a Brazilian airline based in Rio de Janeiro. Between 1945 and 1965, it was considered the largest airline not only in Brazil but in all of Latin America.
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The term GCT, short for Greenwich Civil Time, was introduced in America because conditions had been quite confusing up to that point. In nautical science, 12 noon was the end of the day, and in astronomy the beginning of the day in question.
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In 1884, the International Meridian Conference in Washington expressed the hope in Article VI of its resolutions that “as soon as possible both the astronomical and the nautical day should begin everywhere at midnight.” So Greenwich Civil Time was nothing other than Greenwich Mean Time, but the day now started at midnight.
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One of the few protests against this came from the Royal English Navy, which feared confusion. For her, GCT was the abbreviation for “Gunnery Control Tower”.