Uncrackable codes in WWII
By the time the United States entered World War II in late 1941, radio technology had vastly improved from the equipment available in the 1910s. Vacuum tube radios, which just thirty years ago were bulky and hard to carry, were now smaller. This paved the way for lighter weight, portable, battery-operated transistor radios, encased in metal, for military field use during World War II. In addition to hand-held use by US soldiers on the ground, radios were now an integral part of airplane, submarine, and tank communications. Transmissions went greater distances and were more reliable, and soon became a staple of the war effort.
In order to make radio transmissions more secure, the US Marines employed Navajo, one of the most complex Native American languages, to send messages during World War II. The pilot project began with just 30 Navajo “code talkers,” who soon helped develop a virtually uncrackable cipher based in their native language (including "Moustache Smeller" as a code name for Adolf Hitler).
The program was such a success, particularly against the Japanese, that the Navajo code talkers program grew to 420 men. Navajo code talkers became part of every US Marine assault in the Pacific theater and served in all Marine divisions. Though the Japanese eventually cracked the codes of the US Army and Air Corps, the Marine's Navajo code was never broken.