Code name

Margaretha Geertruida Zelle used the stage name Mata Hari and the code name H 21 when she worked for German Intelligence.

A code name is a secret name used to refer to a name, word, project or person. Spies are often referred to by their code name to make discovery more difficult. Code names may also be used in industrial espionage to protect secrets from business rivals.

Secrecy is not the only reason for their use. Standard words and phrases are easier to hear on radio channels like walkie-talkies.

Code names became numerous in World War II. Names like Operation Barbarossa and Operation Overlord and the Manhattan Project became famous.