On 16 January 1917, German Foreign Minister Zimmermann sent the German Minister in Mexico an enciphered message with a proposal to be presented to the Mexican government. Zimmermann proposed a German-Mexican alliance, with the payoff being Mexico's recovery of the territory lost in the Mexican-American War. British intelligence intercepted and deciphered the message, and turned it over to the Americans on 24 February. Publication of the message raised considerable ire in the United States, and increased popular support for the U.S. declaration of war a few weeks later. See O'Toole, Encyclopedia, p. 508.
For an brief but authoritative version of the Zimmermann Telegram affair, see David Kahn, The Codebreakers: The Story of Secret Writing, rev. ed. (New York: Scribner, 1996), 282-297.
On 17 October 2005, "[c]opies of typescripts of two versions of the Zimmermann Telegram [were released to the British national Archives]. They include comments in Admiral Hall's writing, reading respectively: 'Main line - not exposed' and 'Inland cable on American soil - this was the one handed to Dr Page and exposed by the President'. The file also includes photocopies taken from HW 7/8 of the original manuscript decodes (in Nigel De Grey's handwriting) which led to these typescripts." http://www.nationalarchives.gov.uk/releases/2005/highlights_oct/oct17/default.htm.
Beesly, Patrick. Room 40: British Naval Intelligence, 1914-18. London & New York: Harcourt Brace Jovanovich, 1982.
Pforzheimer views this as the "most comprehensive history now  available of ... the British Admiralty's World War I codebreaking organization." The author "writes lucidly of organizational problems and lessons learned." For Sexton, the book sheds "light on Churchill's passion for and use of ULTRA."
Boghardt, Thomas. The Zimmermann Telegram: Intelligence, Diplomacy and America's Entry into World War I. Annapolis, MD: Naval Institute Press, 2012.
Goulden, Washington Times, 20 Nov. 2012, says the author is able "to dash some prevailing myths and to give a very readable account of the episode.... Boghardt does a superb job of stripping away a veil of misinformation that Britain draped over the story." This work "is a masterpiece of intelligence writing. By following the hard evidence rather than relying on historical assumptions, he provides an incisive case study on how intelligence can affect national affairs"
For Ehrman, Studies 57.2 (Jun. 2013), "Boghardt presents a meticulously researched and well-written account that clarifies the story of the telegram and likely will be the standard for many years to come." This work "is a fine example of how various historical disciplines -- intelligence, diplomatic, and political -- can be combined to tell a compelling story."
Ewing, Alfred W.
1. The Man of Room 40: The Life of Sir Alfred Ewing. London: Hutchinson, 1939.
According to Constantinides, this book, by Sir Alfred's son, does not discuss much about the contribution of the founder of the British navy's cryptanalytic bureau during World War I. Nonetheless, there is little elsewhere on Room 40's early work.
2. "Some Special War Work, Part 1. With an Introduction by David Kahn." Cryptologia 4, no. 4 (Oct. 1980): 193-203. "Some Special War Work, Part 2." Cryptologia 5, no. 1 (Jan. 1981): 33-39.
These articles deal with Sir Alfred's work in Room 40 and the solution of the German diplomatic ciphers in World War I.
Fenton, Ben. "Telegram that Brought US into Great War Is Found." Telegraph (London), 17 Oct. 2005. [http://www.telegraph.co.uk]
"An original typescript of the deciphered Zimmerman Telegram ... has been discovered. The document is believed to be the actual telegram shown to the American ambassador in London in 1917.... [T]he official historian of GCHQ found it while researching an 'official' history of the organisation."
Freeman, Peter. "The Zimmermann Telegram Revisited: A Reconciliation of the Primary Sources." Cryptologia 30, no. 2 (Apr. 2006): 98-150.
Abstract: "A critical examination of the primary sources (some published here for the first time) on the transmission, interception and decryption of the Zimmermann Telegram dispels some long-standing myths and misapprehensions, which are to be traced to inaccuracies in the accounts by the British protagonists in the affair."
Friedman, William F., and Charles J. Mendelsohn. The Zimmermann Telegram of January 16, 1917 and Its Cryptographic Background. Washington, DC: War Department, Office of the Chief Signal Officer, GPO, 1938. Laguna Hills, CA: Aegean Park Press, 1976 and 1994.
Chambers comments that this was the "first US account of the affair"; it is a "little wordy, but very good." According to Constantinides, Barbara Tuchman was unable to gain access to this study for the first edition of her book, and amended her account in a later edition after the 1965 declassification of Friedman and Mendelsohn's work.
Gathen, Joachim von zur. "Zimmermann Telegram: The Original Draft." Cryptologia 31, no. 1 (Jan. 2007): 2-37.
"The orignal Zimmermann telegram ... contains, in addition to the text..., instructions to forward it to Mexico, and minor [wording] variations ... and in punctuation.... [I]n addition, the draft provides valuable information about transmission and encryption."
Harris, Charles H., III, and Louis R. Sadler. The Border and the Revolution: Clandestine Activities of the Mexican Revolution, 1910-1920. Silver City, NM: High-Lonesome Books, 1988. [pb]
Surveillant 1.3 notes that the authors' thesis is "that the modern American intelligence community began during the period of the Mexican Revolution." Archer, I&NS 7.3, comments that the chapters here were first published as separate essays, a fact made clear by the episodic nature of the book. This is not a comprehensive study of clandestine activities along the U.S.-Mexican border in the second decade of the 20th century. There is research here from previously unexplored sources, but the work "does not change major interpretations of the Mexican Revolution."
Hill, Larry D. Emissaries to a Revolution: Woodrow Wilson's Executive Agents in Mexico. Baton Rouge: Louisiana State University Press, 1973.
See review by Calvert, Journal of Latin American Studies 7.2 (Nov. 1975).
Hoy, Hugh C. 40 O.B.: Or, How the War Was Won. London: Hutchinson, 1932.
Constantinides: Much more is known today about Room 40's accomplishments than when this book was published. In its day, it was "an early disclosure of Admiral Hall's activities in British naval intelligence in World War I." Among matters covered are "the Zimmermann note, the case of Sir Roger Casement, the neutralizing of Trebitsch Lincoln, and the capture of Carl Lody."
James, William M. [Admiral Sir] The Eyes of the Navy: A Biographical Study of Admiral Sir Reginald Hall. London: Methuen, 1956. The Code Breakers of Room 40: The Story of Admiral Sir Reginald Hall, Genius of British Counterintelligence. New York: St. Martin's Press, 1956.
According to Pforzheimer, this is the biography of Britain's Director of Naval Intelligence in World War I by the officer in charge of communications intelligence part of that time. "It includes an interesting description of the exploitation of the Zimmermann telegram." Beesly's Room 40 is "perhaps a more useful study." Constantinides argues that although "James has written an important book on one of the outstanding figures of intelligence, not all has been revealed.... Friedman and Mendelsohn's research raises questions as to whether James's cryptanalytic account of the Zimmermann note is the full one."
Jones, R.V. "Alfred Ewing and Room 40." Notes and Records of the Rpya; Society of London 34 (Jul. 1979): 65-90.
Kahn, David. "Edward Bell and His Zimmermann Telegram Memorandum." Intelligence and National Security 14, no. 3 (Autumn 1999): 143-159.
Kahn provides biographic details on the U.S. diplomat who liaised with British intelligence in London with regard to the Zimmermann Telegram. Included are two memoranda by Bell and one by Nigel de Grey, the Room 40 solver of the telegram.
Katz, Friedrich. The Secret War in Mexico: Europe, the United States, and the Mexican Revolution. Chicago: University of Chicago Press, 1981. 1984 [pb]
From publisher: This book "is far more than a diplomatic history of the 1910-1920 era. It is a penetrating analysis of the social basis and leadership of the Mexican Revolution, woven into the story of how Mexican factions used and were used by Europeans and North Americans in the period immediately preceding and during the First World War."
Kelly, Saul. "Room 47: The Persian Prelude to the Zimmermann Telegram." Cryptologia 37, no. 1 (2013): 11-50/
From Abstract: "During the First World War, Persia was the scene of early British cryptanalytical successes against German diplomatic codes and ciphers under the auspices of Room 47.... It is the contention of this article, based on newly discovered archival material, that there is a strong, and previously undetected link with the Zimmermann Telegram."
Nickles, David Paul. Under the Wire: How the Telegraph Changed Diplomacy. Cambridge, MA: Harvard University Press, 2003.
Kruh, Cryptologia 28.2, notes that this "interesting study by a knowledgeable author ... includes an excellent discussion of the Zimmermann Telegram incident." To Steury, Studies 48.3 (2004), the author's "arguments are thought-provoking and he never fails to interest.... Nickles draws the appropriate security lessons from the Zimmerman[n] episode and highlights [head of Royal Navy signals intelligence Rear Admiral Sir Reginald 'Blinker'] Hall's success in deceiving both the US and Imperial German governments about how he obtained the telegram."
Tuchman, Barbara W. The Zimmermann Telegram. New York: Viking Press, 1958. London: Constable, 1958. New York: Scribner, 1966. New York: Bantam, 1971. [pb] New York: Ballantine, 1985. [pb] London: Phoenix, 2001.
Constantinides sees the British interception and deciphering of the Zimmermann telegrams as "one of the greatest and most significant cryptanalytic successes in history." Tuchman's account suffers from having been written before the 1965 declassification of Friedman and Mendelsohn, The Zimmermann Telegram of January 16, 1917 and Its Cryptographic Background (1938). Pforzheimer says this book is "[r]eadable and well documented," and "provides an outstanding example of the impact of intelligence on the course of history."
U.S. Congress. Senate. Committee on Foreign Relations. Investigation of Mexican Affairs, Reports and Hearings. 2 vols. 66th Cong., 2nd sess. Sen. Doc. 285. Washington, DC: GPO, 1920. [Petersen]
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