The u. s. military first experimented with native american languages in military intelligence

The correct answer here is the World War I.
Maybe the most recognizable and most famous code talkers in the US military history were the Navajo Code Talkers which operated during the World War II but this was actually pioneered in the World War I where we see the first instances of experimenting with the Native American Languages as a source for military code. In the World War I, Cherokee and Choctaw peoples were the ones to do this.