The Republic of Ireland used for its secret diplomatic communications the British Government Telegraph Code, a five-letter, one-part, 84,000 group system. This was used unenciphered for low level messages and enciphered for more important traffic. The Germans had managed to capture a copy of the Government Telegraph Code from the British consulate in Bergen, Norway in 1940.
The section of Pers Z that was responsible for Irish codes was Dr Ursula Hagen’s group. This covered England, Ireland, Spain, Portugal and Latin American countries. Technical Assistant (Wissenschaftliche Hilfsarbeiterin) Dr. Ursula Hagen was born March 23, 1901. She entered Pers Z S on October 1, 1922 and by 1939 (and through 1945) she was head of the group which was responsible for work on England, Ireland, Spain, Portugal, and Latin American countries. In 1942 her group had 12 people assigned to it (1).
Irish codes were also worked on by Goering’s Forchungsamt. The Forschungsamt’s Abteilung 7 had considerable success (‘ziemlich laufend’) with Irish codes up to the end of the war (2). Abt. 7 covered: USA, England, Ireland, South America, Spain, Portugal, Turkey, Egypt and Far East. Personnel were roughly 60-70.
More details on the Irish codes are given in TICOM I-172 ‘Interrogations of Hagen and Paschke of Pers Z S’, p3-4
HAGEN described the work done by Pers Z S on Irish Diplomatic substitution recoding tables for use with G.T.C. There were 26 hatted alphabets, each group being taken from one alphabet. The alphabets were not necessarily used in order but always systematically. The last group of a telegram indicated the system to be used in the next message, e.g, if the last group was recyphered with alphabet 5, then this alphabet would also be used for the first group of the next message. The tables changed at irregular intervals - only about four times during the war. Different keys were used for various posts, e.g. Berne, Rome, Berlin, Paris, Madrid. The traffic became more difficult to read in 1942-43, when there was insufficient material and not enough staff. Then the Forschungsamt started work on it and solved the Berlin and Madrid links. Pers Z S took over the keys from the Forschungsamt in 1944. The first three figures of the message gave the page number, the fourth figure the number of the block, and the fifth and sixth figures the line-numbers. This new system used a 300-figure subtractor; each end of the link was allotted 25 such keys, e.g. 25 Dublin-Berlin and 25 Berlin-Dublin, etc. If the length of the message exceeded 300 figures, the key was repeated, but a new key was used for each new message, always in the order 1 to 25.
Messages consisted of reports from the Irish minister on the state of affairs in Germany. The Staatssekretär was interested in diplomatic reports on the trend of events, air-raids; etc. The traffic was regarded as valuable by Ribbentrop and some messages were shown to Hitler. HAGEN said that with any luck six fairly long messages were sufficient to break a new substitution recoding table, and this work took less than a week.
Irish messages in plain G.T.C. did not provide information of any value.
Translated Pers Z reports from 1941 and 1942 confirm these statements (3). The 1941 report says that ‘all the Irish telegrams can be read completely’ and 223 decoded telegrams were published. In 1942 126 decoded telegrams were published.
Some decrypted Irish telegrams from 1944 can be found in the TICOM collection of the German Foreign Ministry’s Political Archive (4), for example:
(2). TICOM report I-54 ‘Second interrogation of five members of the RLM/Forschungsamt’, p2-3
(3). British national archives HW 40/180 ‘PERS Z-S, the Diplomatic Decryption Bureau of the German Ministry of Foreign Affairs: reports and POW interrogations’ (Annual report of section dealing with British empire, Eire, Thailand, Portugal, Spain and Latin America).
(4). German Foreign Ministry’s Political Archive - TICOM collection – File Nr. 795 Irland 1944 Entschl. Verkehr (übersetzt) zw. d. versch. Irischen Botschaften