Final answer:
The main difference between codes in WWI and WWII was that WWII codes, such as those by Navajo code talkers, were more complex and employed a highly sophisticated system utilizing unique elements of the Navajo language.
Step-by-step explanation:
One difference between the codes used by Native American code talkers in World War I and World War II was the structure and complexity of the codes. In World War I, soldiers like the Choctaw code talkers transmitted messages using their indigenous languages in a relatively straightforward manner, without a formalized code system. By World War II, specifically with the Navajo code talkers, the code system had been developed into a highly sophisticated code beyond the mere use of native languages. This new code integrated Navajo words that, when translated, had an English equivalent starting with the same letter necessary to encode a message, such as "iron fish" for "submarine". Moreover, the Navajo language's lack of a formal alphabet and few non-native speakers added to the code's indecipherability to Axis power intelligence.