New geographical terminology was developed for the specific islands and regions where Marine operations were occurring or planned.

The substitution alphabet was refined and the multiple representations for each letter were standardized to reduce the potential for confusion under stress.

Each expansion of the code required corresponding expansion of the training program.

New recruits to the Code Talker program had to learn not only the original vocabulary but each subsequent addition, all entirely from memory.

The training curriculum grew more demanding as the code grew more comprehensive.

The men who trained the expanding cohort of Code Talkers were largely veterans of earlier deployments — men who had used the system in combat and who understood from direct experience where it was robust and where it required careful handling.