Final answer:
The device used to help the United States decode Japan's radio transmissions during World War II was the use of the Navajo language by the Navajo code talkers. Their unique contributions aided secure communication in the Pacific Theater and were never deciphered by enemy forces.
Step-by-step explanation:
The decoding device that helped the United States decipher Japan's radio transmissions during World War II was not a single machine, but rather a group of individuals known as the Navajo code talkers. These code talkers utilized the Navajo language, which was unwritten and highly complex, to encode and transmit messages. The enemy was unable to decipher these communications as they were intelligently coded. The Navajo code talkers became a crucial part of the U.S. war effort, transmitting coded messages that were never broken by Japanese intelligence.
In addition to the use of the Navajo language for encoding messages, British code breakers also cracked Germany's Enigma radio cryptography during the war. This intelligence was vital for the Allies, helping to win crucial battles such as the Battle of the Atlantic.
The contribution of the code talkers demonstrates the innovative and strategic use of indigenous languages to maintain secure communications during wartime. Despite attempts by the enemy to crack these codes, the dedication and unique skills of the Navajo code talkers provided the Allies with a significant advantage in the Pacific Theater.