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Identity statement

Reference code(s)
ULTRA: British Intelligence Messages based on decoded German Signals, 1941-1945
Level of description
collection level
Extent and medium of the unit of description (quantity, bulk, or size)
139 reels


Name of creator(s)
Government Code and Cypher School, Bletchley Park, Buckinghamshire
Administrative / Biographical history
ULTRA was the British classification developed in 1940 to denote the new and highly secret intelligence material produced by the decryption of intercepted German and Italian radio messages enciphered in the ENIGMA cipher machine, transmitted on the German Geheimschreiber machine, or enciphered on the Italian C38m machine cipher. ULTRA was the collective term for the body of decrypted Axis messages. As such, it was not the product of a single cipher, but of many. By 1945 almost 200 ENIGMA variants were known, not all of which were broken. Government cryptographers formed the nucleus of the work-force at Bletchley Park, the remainder being filled mainly by mathematicians, mathematical theorists, and statisticians. Throughout the war and in one form another, ENIGMA was an integral component of German Armed Forces planning and communication, from land forces theatre communications to Supreme Command of the German Armed Forces (OKW) directives to the German Navy. The success of ULTRA was due to the fact that ENIGMA was thought by the Germans unbreakable and was used widely throughout World War Two, thus making it susceptible to decryption. In addition, there was a gradual dilution in the quality of German personnel operating the encrypting machines whilst the number of encoded messages increased exponentially from 1941-1945. As a result, by the end of the war, Allied intelligence personnel had decrypted thousands of Axis operational messages. The roots of what was eventually to become ULTRA lay with a group of Polish mathematicians. The ENIGMA machine was developed in Poland the 1920s, it rights later being bought up by the German Armed Forces. In 1931, a member of the German Foreign Ministry gave some sheets of the ENIGMA instruction manual to a French military cryptographic bureau, the first of many future transactions. The French then offered copies of the files to the Poles and the British, the latter of whom were initially disinterested. By the late 1930s, the Poles were reading a great deal of the traffic passed in the new cipher. Feeling the growing threat from Germany in Jul 1939, they presented both the French and the British with one of the machines they had constructed since 1931. By this time, however, mathematicians at the Government Code and Cypher School at Bletchley Park had advanced beyond the capabilities of the Poles. From Mar 1941, the Allies were able to decrypt and then read official correspondence derived from thoroughly reliable sources within the higher echelons of the German Armed Forces and Foreign Ministry. By necessity, it presented only a selection of German correspondence and messages, which then could be put into probable contexts. From 1940 to 1945, British cryptographers increased their understanding of the ENIGMA variants, and while the initial series of decryption appeared too late to affect the Battle of France, 10 May-22 Jun 1940, ULTRA did give general forewarnings of the state of German preparations for the invasion of Britain and the move of German forces east in preparation for the German invasion of the Soviet Union. From 1941 to 1945, there was regular daily decryption of ENIGMA messages, enough to allow for the dispersal of key information to field commanders. By 1944, Bletchley Park staff were also authorised to submit messages to Allied field commanders, which were then analysed by Special Liaison Units in the field. Special sections at Bletchley Park were also established for naval messages relating to North Sea and Mediterranean Sea operations and the protection of Atlantic supply routes from German U-boats. By Apr 1943, the first American cryptological and intelligence group arrived at Bletchley Park and, despite British misgivings about losing their secret, a formal agreement to share ULTRA with the US was concluded in May 1943.
Immediate source of acquisition or transfer
The National Archives, Kew, Surrey

Content & structure

Scope and content
ULTRA: British Intelligence Messages based on decoded German Signals, 1941-1945 is a microfilm copy of file copies of decrypted teleprinter messages held at the National Archives, Kew (DEFE 3), relating to operational intelligence from intercepted German and Italian radio communications, 1941-1945. These signals became known as ULTRA. The various series of the messages are of two distinct types: intercepted signals, decrypted, translated, and sent from the German Naval Section of the Admiralty's Naval Intelligence Centre in the Admiralty; and summaries of intelligence derived from such signals sent to the War Office, Air Ministry, and overseas commands. The collection includes translated messages relating to the German invasion of Yugoslavia, Greece, Apr 1941; forewarnings of the impending German invasion of Crete, May 1941; Operation CRUSADER, 8 Army operations in the Western Desert, Nov 1941-Jan 1942; German Air Force cover of Mediterranean transport operations, Nov 1941-Jan 1942; forewarnings of the advance in the Western Desert of German Armed Forces under the command of Col Gen Erwin Rommel, Aug 1941; German surface vessel and U-boat communications, Aug 1941-Feb 1942; Allied victory over German U-boats in the Atlantic, 1942-1943; the delay of 8 Army, under the command of Gen Bernard Law Montgomery, at Mersa el Brega, Libya, Dec 1942; the Allied campaign in Sicily, Jul 1943; the Italian surrender and the Allied landing in Italy, Sep 1943; Adolf Hitler's decision to stand on successive defensive lines in Italy, Oct 1943; forewarning of FM Albert Kesselring's decision not to advance beyond his attack at Anzio, Italy, Feb 1944; and collected intercepts which identified the German divisions manning the coastal defences in the Pas de Calais, France, Jun 1944.
System of arrangement
Arranged into series according to source of decryption and subject matter, and chronologically therein. For example, the first series relates to intelligence from enemy radio communications, Mar 1941-Apr 1945; the second series are decrypted German signals, Mar 1941-May 1945, which includes teleprinted translations of decrypted messages; the third series are Allied intelligence messages based on intercepted signals, Jul 1942-May 1945. All series in the microfilm collection have corresponding National Archives (DEFE 3) reference numbers.

Conditions of access & use

Conditions governing access

Open, subject to signature of Reader's undertaking form, and appropriate provision of two forms of identification, to include one photographic ID.

Conditions governing reproduction
Copies may be printed off the microfilm for research purposes and are charged at the cost to the Centre. Enquiries concerning the copyright of the original material should be addressed to the National Archives, Kew, Richmond, Surrey, TW9 4DU.
Language/scripts of material
Finding aids
Summary guide entry online and catalogue available in hard copy in the Centre's reading room.

Allied materials

Existence and location of originals
The National Archives, Kew, Surrey
Existence and location of copies
National Archives and Record Administration, Washington, DC.


Compiled Oct 1999

Description control

Rules or conventions

Compiled in compliance with General International Standard Archival Description, ISAD(G), second edition, 2000; National Council on Archives Rules for the Construction of Personal Place and Corporate Names 1997.

This catalogue is made available under the Open Data Commons Attribution License. This catalogue may be updated from time to time in order to reflect additional material and/or new understandings of the material.

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