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

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

for the 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