World War I: Communications-British Signals Intelligence


Figure 1.--

The British during World War I did not have a centralized code breaking effort. The Army and Royal Navy had theior own separate signals intelligence agencies. The Army unit was MI1b. The Royal Navy unit was NID25 (Room 40). The Russians obtained a major intelligence prize early in the War. They found a code book on the the German cruiser Magdeburg which had run aground in the Baltic. The vRussians turned it over to the British. This gave the British insights into German secure communications for most of the War. Naval intelligence during the War, however, was primarily assessing the direction and volume of transmissions. One of the most important examples of code breaking was the British decryption of the Zimmerman Telegran, a factor in bringing America into the War. The American public was outraged. When Germany resumed unrestricted submarime warfare, there waslittle opposition to entering the War.

Cryptographic Units

The British during World War I did not have a centralized code breaking effort. The Army and Royal Navy had theior own separate signals intelligence agencies. The Army unit was MI1b. The Royal Navy unit was NID25 (Room 40), also referred to Old Block. NID25 was run by Cpt. Hall. This was tghe group that managed to crack 0075 and the Zimmermann Telegram.

German Diplomatic Codes

The German Foreign Ministry had no way of communicating with its embassuies in The United States and North America. They had to use cables that went through Britain. Thus they coded the messages. One of those codes 0075. This code system was judged to be impossible to crack, It contained about 10.000 phrases and individual words. One codebook was used to transmit and another to decode. They proved to be very wrong. This was the code used for the famous Zimmerman telegram. This was surely one of the greatest cryptographic fiascos in history.

German Naval Codes

The Russians obtained a major intelligence prize early in the War. The German cruiser Magdeburg ran aground in the Baltic. A series of German misteps allowed the Russians to get their hands on the the ship's codebook. The Russians turned it over to the British. The Imperial German Naval code was thus an open book to the British who already had an overwealming superority. And even worse the Germans did not know or convinced themselves that their code had been compromosed. This gave the British major insights into German secure communications for much of WorldWar I. Naval intelligence during actual combat opetations, however, was primarily traffic analysis, assessing the direction and volume of transmissions without actually being able to read them.

German Army Codes


Zimmerman Telegram

One of the most important examples of code breaking was the British decryption of the Zimmerman Telegran, a factor in bringing America into the War. Britain controlled the trans-Atlantic cable links to America. The Germans used the cables to send telegram messages to their diplomatic missions in America. The Germans encoded sensative messages, assuming the British could not read them. German Foreign Minister Arthur Zimmerman sent a coded message to the German Ambassador in Mexico von Eckhardt (January 16, 1917). It instructed him to inform the Mexican Government that Germany would soon resume unrestricted submarine warfare which in a few months would knock Britain out of the War. The Germans assumed this would cause America to declare war. Zimmerman offered Mexico U.S. territory if Mexico would join Germany in the war. We are unsure about the German decession-making process. Surely the failed Mexican expedition must have been a factor. The telegram read, "We intend to begin on the first of February unrestricted submarine warfare. We shall endeavor in spite of this to keep the United States of America neutral. In the event of this not succeeding, we make Mexico a proposal or alliance on the following basis: make war together, make peace together, generous financial support and an understanding on our part that Mexico is to reconquer the lost territory in Texas, New Mexico, and Arizona. The settlement in detail is left to you. You will inform the President of the above most secretly as soon as the outbreak of war with the United States of America is certain and add the suggestion that he should, on his own initiative, invite Japan to immediate adherence and at the same time mediate between Japan and ourselves. Please call the President's attention to the fact that the ruthless employment of our submarines now offers the prospect of compelling England in a few months to make peace." Signed, ZIMMERMANN." It was possible the most blatantly incompetent diplomatic approach in history. We are not sure to what extent the Kaiser was involved, but Zimmerman would not have made this offer without the Kaiser's approval. British Naval Intelligence cryptographers using a captured German codebook decoded the message. were surprised when a encoded German transmission came across their desks. German actions in the War, especially in Belgium and on the highseas had brought most Americans over to the Allied side, although public opinion still opposed entry in the war. The British turned the telegram over to the American Embassy in London (February 24, 1917). The Wilson Administration released the telegram to the press (March 1). Some at first thought the telegram a forgery which the Germans and Mexicans first claimed. Zimmerman inexplicteldly admitted he had sent the message (March 3). The American public was outraged. Public opinion shifted toward a declaration of war. [Tuchman] Despite substantial pascifist sentiment, there waslittle opposition to entering the War.

Code and Cipher School (1919)

The British Government created the Code and Cypher School (GC&CS) in the aftermath of World War I (November 1919). The British after the War made many adjustments as the wound down the massive military effort. Officials burdened with a massive War bebt looked at how various war time operations could be cutback to reduce costs. The Cabinet's Secret Service Committee, chaired by Lord Curzon, recommended that a single, centralized peace-time codebreaking agency should replace the separate service cryptology units. The Director of Naval Intelligence, Hugh Sinclair was assigned the task of leading the new GC&CS. Sinclair merged the staff of the war time Naval NID25 and Army MI1b units to create the new organization. It was a relatively small organization, about 25–30 officers and a comparablr number of clerical support staff. Victor Forbes in the Foreign Office chose the name to desguise the agency's purpose. GC&CS was ininitally assigned to the Admiralty in facilities at Watergate House, Adelphi, London. The function for public consumption was to "to advise as to the security of codes and cyphers used by all Government departments and to assist in their provision." Ther was a secret directive to "study the methods of cypher communications used by foreign powers." In the new peacetime enviroment, GC&CS focused primarily on diplomatic traffic. As a result, at the suggestion of Lord Curzon, the agency was transferred to the Foreign Office (1922).






HBC







Navigate the Boys' Historical Clothing Web Site:
[Return to Main World War I signals intelligence page]
[Return to Main World War I intelligence communications page]
[Return to Main World War I intelligence page]
[Return to Main World War I page]
[Return to British World War II code breaking]
[Introduction] [Activities] [Biographies] [Chronology] [Clothing styles] [Countries]
[Bibliographies] [Contributions] [Essays] [FAQs] [Glossaries] [Images] [Links] [Registration] [Tools]
[Boys' Clothing Home]



Created: 10:19 PM 2/24/2011
Last updated: 5:28 PM 3/21/2011