The British designation for intelligence obtained by breaking the enemy's most important communications at Bletchley Park.
Description based on the Crypto Museum's crypto glossary. The International Spy Museum describes Ultra as the code name for intelligence obtained from decrypting German messages enciphered on the Enigma during the Second World War.1,2
The starting point was the work of Polish cryptologists. According to the Foreign Office historian Gill Bennett, on 26 July 1939 at Pyry near Warsaw the Poles revealed to the British and the French that they had been reading Enigma traffic since 1933; Dilly Knox of Bletchley Park recognised the importance of the Polish achievement, which shortened the British attack on Enigma by at least a year.3
Ultra intelligence supported, among other things, Britain's deception game: according to MI5, the Bletchley Park codebreakers provided indispensable support for the Double-Cross System. According to GCHQ, breaking German communications, especially those enciphered on Enigma, contributed significantly to the Allied victory.4,5
Sources
- Crypto Museum, Crypto glossary
- International Spy Museum (Washington, DC), Language of Espionage (glossary)
- Gill Bennett, blog of the UK Foreign Office historians (history.blog.gov.uk), What’s the context? Polish cryptologists reveal they have cracked the Enigma code, 26 July 1939 (26.07.2019)
- MI5 (Security Service), MI5 in World War II
- GCHQ, 100 years of GCHQ (2019)
Checked: 4 November 2026