United States Inverted Jenny, 1918

The Inverted Jenny is a twenty-four cent United States airmail postage stamp, originally issued on 10 May 1918 to inaugurate regular airmail service between Washington, D.C., Philadelphia, and New York City. Designed by Clair Aubrey Huston and engraved by Marcus Baldwin, the issue served as the first airmail stamp released by the United States Post Office. The stamp is distinguished by a production error in which the central aeroplane image was printed upside down relative to its outer frame.

Production of the stamp was carried out under tight deadlines, with engraving commencing on 4 May and printing on 10 May 1918. Printed on a flat-bed press in sheets of one hundred, each sheet required two separate impressions to apply the two ink colours. The red frame was printed first, followed by the blue vignette. An error occurred either because a sheet of printed frames was placed into the press upside down for the second run or because the vignette plate was mounted inverted. While three misprinted sheets were detected and destroyed during production, a single sheet of one hundred inverted stamps passed unnoticed into circulation and was obtained at a post office by collector William T. Robey on 14 May 1918.

The design features an ornamental red frame surrounding a blue Curtiss JN-4HM biplane, a model modified with increased fuel capacity and the removal of a pilot seat to accommodate mailbags. The perforated stamp depicts aircraft number 38262. In examples where the blue vignette is printed off-centre and overlaps the border, the blue ink lies on top of the red ink, demonstrating the sequence of the two printing passes.