allowing heavy shells to be fired from relatively lightweight guns. Fonó submitted his invention to the Austro-Hungarian Army, but the proposal was rejected. After World War I, Fonó returned to the subject. In May 1928 he described an "air-jet engine" as suitable for high-altitude supersonic aircraft, in a German patent application. In an additional patent application, he adapted the engine for subsonic speed. The patent was granted in 1932 (German Patent No. 554,906, 1932-11-02).

Soviet Union