Intercepted Radio Communication in World War II.

The messages transcribed for this project were intercepted, decrypted, translated, and sent from the German Naval Section of the Admiralty's Naval Intelligence Division at Bletchley Park to the division's Operational Intelligence Centre in the Admiralty.

Telecommunication is defined as communication over a considerable distance using technology such as  wireless telegraphy . With the Second World War came a rise in the need for secure message transmission.

Reliable radio technology  advanced in quality and quantity  throughout the war and, thus, the need to protect these messages became paramount. Both sides of the war began to develop methods of encrypted communication that kept radio messages indiscernible to unintended audiences.

For the Germans, this method of encryption was considered unbreakable to many. They relied on a machine known as the  Enigma , which could produce  highly encrypted text messages  with the use of rotors and a plugboard.

There were approximately  150 million million  different combinations possible for each intercepted message by the Allies.

Plain text messages that were sent through the machine came out seemingly entirely randomly scrambled but could be interpreted by a recipient with the correct rotor and plugboard settings.

Enemy messages were obtained by a chain of intercept stations called the  Y service  which were found across Britain and various other countries. Each station was called a Y station and could intercept wireless and radio telecommunications.

Intercepted messages were transcribed carefully by operators and then sent to Bletchley Park to be deciphered.

The map below contains detailed information regarding the precise and estimated locations of some Y stations. Additionally, this map contains information about advanced  Direction Finding  (DF) stations.

Despite its complex encryption system, an operator only needed to know the starting position, and order, of (at least) three rotors and the positions of the plugs in the plugboard in order to  send an enciphered message .

On the receiving end, the other operator would set the machine to the same rotor and plugboard settings to decipher the message. To communicate the rotor and plugboard settings, physical codebooks were distributed to operators to ensure identical Enigma settings across all machines for each day. 

Many historians, mathematicians, and cryptanalysts agree that the Enigma  might have remained unbreakable  had the Germans operated the machine perfectly. However, human error while operating the machine resulted in several hints that the British used to undermine the crypto-system. For example, commonly repeated phrases, such as weather reports, allowed cryptanalysts to guess where the words “weather report” might appear and determine what rotor settings were used for that day. Other situations, such as the British obtaining a codebook for that month, resulted in insight into Enigma's setting structure, such as the lack of repeated settings each month.

Each day was a race to find the rotor and plugboard settings in order to decrypt any ciphered messages by brute-force methods. Eventually, the need to mechanize this process was crucial for the Allied powers to win the war. With much progress initially completed by Polish mathematicians with their  Bomba , British mathematicians and scientists, including  Alan Turing , began work on the  Bombe  in 1939.

Named after the Polish bombas, the machine aimed to find the daily rotor and plugboard settings in order to crack the thousands of intercepted messages daily. With around 100 rotating drums, 16 km (10 miles) of wire, and about one million soldered connections, the machine started finding Enigma settings in  only a few hours . Members of the Women’s Royal Naval Service, or  WRNS , operated the machine for several hours at a time in extremely stressful conditions. By the end of the war, "the Admiralty had received an overall total of 271,118 such messages" (Harrison, 15).

The map above is a snapshot of the messages that would have been intercepted and read at Bletchley Park for about two weeks. All data transcribed is from between June 4th-17th 1944. Below include a diverse selection of intercepted messages that were used for the mapping data.

Because it was less pertinent, the 'to' and 'from' at the very top of each typed message was ignored as to only focus on the intercepted message at hand.

Though many of these messages center around the Mediterranean, the majority of the password communication occurred to or from radio stations in German occupied France.

The efforts of the Y service interceptors was pivotal for the Allied victory of the Second World War. Several messages with valuable intelligence were uncovered because of their work, such as German Naval Operation plans and password communication.

Focusing on a sliver of the intercepted messages was necessary, as there were around 500 messages across late May to late June in the National Archive's dataset. The data centered around a critical turning point in the war as well, as D Day occurred on June 6th 1944, which was an ambitious mission that  ultimately changed the outcome of the war .

The goal of this project was to highlight the codebreaking efforts of the Second World War while exploring the intercepted data in a modern context. Major developments in telecommunication and computing occurred in this period, and studying the digital records of interceptions allows us to gain context surrounding the breakthroughs in cryptography and intelligence gathering.