Ultra (sometimes capitalised ULTRA) was the name used by the British for intelligence resulting from decryption of encrypted German radio communications in World War II. The term eventually became the standard designation in both Britain and the United States for all intelligence from high-level cryptanalytic sources. The name arose because the code-breaking success was considered more important than the highest security classification available at the time (Most Secret) and so was regarded as being Ultra secret.
Much of the German cipher traffic was encrypted on the Enigma machine, hence the term "Ultra" has often been used almost synonymously with "Enigma decrypts". However, in terms of the intelligence value, Lorenz SZ 40/42 decrypts were more important.
Until the name "Ultra" was adopted, there were several cryptonyms for intelligence from this source, including Boniface. For some time thereafter, "Ultra" was used only for intelligence from this channel.
