Final answer:
The Navajo code was the method that helped the U.S. intercept Japanese communications during WWII. It used the complex Navajo language, which made the code virtually unbreakable. Alan Turing, while key in decrypting the Nazi Enigma code, was not related to the Japanese communication interception efforts.
Step-by-step explanation:
The decoding device that helped the United States decipher Japanese radio communications during World War II was the Navajo code. This was not a physical device but a method of communication using the Navajo language, which was spoken and understood only by the Navajo people. Utilizing their indigenous language, the Navajo Code Talkers were crucial for sending top-secret messages that could not be deciphered by enemy forces. It was a code based on the complex and unwritten Navajo language that made it virtually unbreakable. The use of the Navajo language as a military code came after the successful use of choctaw language in World War I, and it was particularly effective during the Pacific campaigns.
The British mathematician Alan Turing was instrumental in developing an electromagnetic device called the Bombe, which was used to decrypt the Nazi Enigma code, although this was not directly related to Japanese radio communications during World War II. The efforts of the Code Talkers and scientists like Turing contributed significantly to the development of modern computing and cryptography.