The Junkers J 1, nicknamed the Blechesel (Tin Donkey or Sheet Metal Donkey), was an experimental monoplane aircraft developed by Junkers. It was the first all-metal aircraft in the world. Manufactured early in the First World War, an era in which aircraft designers relied largely on fabric-covered wooden structures braced with wires, the J 1 was a revolutionary development in aircraft design, making extensive use of metal in its structure and in its outer surface.
The J 1 originated from the work of pioneering aeronautical designer Hugo Junkers. The experimental aircraft never received an "A" or "E-series" monoplane designation from IdFlieg, the Army inspectorate of military aircraft and The Imperial German Air Service (Die Fliegertruppen des deutschen Kaiserreiches).