Engineers next investigated the feasibility of balloon launches against the United States from the Japanese mainland, a distance of at least . Engineers sought to make use of strong seasonal air currents discovered flowing from west to east at high altitude and speed over Japan, today known as the jet stream. The currents had been investigated by Japanese scientist Wasaburo Oishi in the 1920s. In late 1943, the Army consulted Hidetoshi Arakawa of the Central Meteorological Observatory, who used Oishi's data to extrapolate the air currents across the Pacific Ocean and estimate that a balloon released in winter and that maintained an altitude of could reach the North American continent in 30 to 100 hours. Arakawa further found that the strongest winds blew from November to March at speeds approaching .
Engineers next investigated the feasibility of balloon launches against the United States from the Japanese mainland a distance of at least  Engineers sought to make use of strong seasonal air currents discovered flowing from west to east at high altitude and speed over Japan today known as the jet stream The currents had been investigated by Japanese scientist Wasaburo Oishi in the 1920s In late 1943 the Army consulted Hidetoshi Arakawa of the Central Meteorological Observatory who used Oishi's data to extrapolate the air currents across the Pacific Ocean and estimate that a balloon released in winter and that maintained an altitude of could reach the North American continent in 30 to 100 hours Arakawa further found that the strongest winds blew from November to March at speeds approaching 