According to paratrooper Gerard Devlin, this exclamation dates from August 1940 and is attributed to Private First Class Aubrey Eberhardt, member of parachute test platoon at Fort Benning.
On the eve of their first jump, the platoon decided to calm their nerves by spending the day before taking in a film at the Main Post Theatre and a night at the local beer garden.
To prove to you that I'm not scared out of my wits when I jump, I'm gonna yell Geronimo loud as hell when I go out that door tomorrow!"
It was said that one day Geronimo, with the Army in hot pursuit, made a leap on horseback down an almost vertical cliff, a feat that the posse could not duplicate.
[6][7][8] By then, the coverage of the paratroopers' exploits during World War II had made the cry "Geronimo" known to the wider public, and its use spread outside the military and U.S. Army.