Navajo code talkers
US Marines who ran WWII radio traffic in a code layered on top of the Navajo language — one the Japanese never broke.
The idea came from Philip Johnston, an engineer raised on a reservation who knew that almost nobody outside it spoke Navajo. The first 29 recruits arrived in 1942 and built the code themselves: everyday words stood for letters (wol-la-chee, ant, for A) and military terms got descriptive stand-ins — a submarine was an "iron fish", a tank a "tortoise". Around 400 men served in all.
The point was speed rather than cryptographic strength: a message that took half an hour on a cipher machine went through in seconds. At Iwo Jima in 1945, six code talkers sent more than 800 messages without an error. The programme stayed classified until 1968, and the Congressional Gold Medal only arrived in 2001. The Army had already tried the same trick with Choctaw speakers in 1918.