The year is 1942. The U.S. is fighting in World War II—the deadliest war in history. Japanese troops have taken over much of the Pacific Ocean. American forces are battling to win back the territory. Communication is a big challenge. The U.S. Marines rely on radio to transmit important battle strategies. But the American forces don’t want their plans to be discovered by the opposition. They use cryptography—the science of secret writing—to create coded messages. Unfortunately, the Japanese military has many skilled code breakers. They intercept and decipher these encrypted radio messages, figuring out America’s every move. The Marines need to create a code their enemy can’t break.