Geronimo

 
The Apache leader Geronimo died on this date in 1909 at the age of approximately 80.  THC came across the story of how Geronimo became the U.S. paratrooper yell when jumping out of aircraft.   According to b-westerns (found via VA Viper), it originated spontaneously in 1940, possibly inspired when Private Aubrey Eberhardt and three other paratroopers in training saw the film Geronimo:

After the movie and a drink at the nearby beer garden, the foursome began their walk back to their lowly tents on the airfield. During that fateful mile they would stumble into a conversation that would ultimately bring Geronimo into a whole new genre. One of the group asked Eberhardt if he thought he could jump out of the plane the next day without fear. Eberhardt, not used to having his confidence questioned, responded that he would not be scared and to prove it, he would let his fellow paratroopers know that he could keep his presence of mind by yelling something to them right after he jumped out. Although the group would be separated by hundreds of feet, with some in the air and some on the ground, Eberhardt insisted he could yell loud enough to be heard by all. When asked what he would yell, he thought for a few moments for a good word to choose - one that was distinctive enough that no one else would be using it. It is probable that he dismissed common salutations such as, "Hey!" or "It's me!" because he would take no chance that anyone would think his shout could be someone else. In the few moments it took him to think of such a unique word, his mind must have gone back to the movie and the inspiring sight of Chief Thunder Cloud. "Geronimo" was the word he chose.

The next day he fulfilled his promise. Eberhardt's fellow paratroopers heard the word, "Geronimo" repeatedly fill the air from the moment he jumped out until his feet touched the ground! Others in the platoon picked up on the idea in their subsequent parachute jumps and the beginnings of a tradition formed in the skies above Lawson Army Airfield as more of the platoon mimicked Private Eberhardt's bold, mid-air yell. 

The most interesting part to THC was how the use of Geronimo became more formal and widespread with the permission of his family:

Major William Miley, [commander 501st Parachute Infantry Battalion], gave the Geronimo tradition an important endorsement by choosing "Geronimo" as the motto on the 501st PIB unit insignia, a device worn on the dress uniform of every soldier in the unit. Maj. Miley even had sergeant major locate relatives of the real chief Geronimo to ask their permission for use of the chief's name in the unit insignia. He located them with the help of the Bureau of Indian Affairs and they granted permission with pride.

Since WWII, the name of Geronimo has been used to signify bravery in the military services and the U.S. even has an Apache helicopter.  For this reason it raised some understandable consternation within the Apache nation when it was learned that Geronimo was the U.S. government code name used for Osama bin Laden during the 2011 raid in which he was killed.