The ''Communications Machine'', or "CM", is a mechanical device used by the

United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

for most of the 1920s. It used a sliding alphabet system. It was developed by Agnes Meyer Driscoll and William Gresham. In 1937 the United States Congress recognized the achievement of these two by awarding them both $15,000.

References

Encryption devices {{Cryptography-stub