Philip Johnston, a missionary's son, grew up on a Navajo reservation. In WWII, the Japanese cracked every code the Americans could encrypt. Johnston knew that the Navajo language had no alphabet or written record, and was near impossible to learn if you weren't immersed in it as a kid. He alerted the military of this, staging a demonstration. Because of him, the Navajo Code Talker program began, the only undecipherable code in modern military history.