In World War II, the US military organized paratroopers to conduct air combat. The night before paratroopers organized skydiving, I happened to watch a feature film about geronimo. In order to boost morale, they agreed to shout "geronimo ~" when they started dancing the next day. This has since become a tradition of American airborne troops. Perhaps, paratroopers will encounter unpredictable situations after parachuting, and they need courage and wisdom like geronimo. Nowadays, many western troops or people will shout "geronimo ~" when parachuting.