Top Secret Messages of World War II. During World War II U.S. forces had to keep battle plans and othertop secret information out of the enemys hands. Coded messageswere often used, but secret codes could be broken. To solve thisproblem, the U.S. military turned to an unexpected source to createan unbreakable code. The Navajo people spoke a complexlanguage that few outsiders knew how to speak. Several Navajosoldiers were recruited to develop a code based on the Navajolanguage. The result was a complex code that could not be brokenby the enemy.