ROOM 40: British Naval Intelligence and the Zimmermann Telegram

Lesson Author
Lesson Abstract
Students role play British intelligence experts who must examine the decoded Zimmerman Telegram and determine the best way to handle this potentially explosive information and act accordingly.

Cooperative learning through Student Role Play and Primary Source Analysis

District, state, or national performance and knowledge standards/goals/skills met

Missouri Standards

6. Relationships of the individual and groups to institutions and cultural traditions

7. The use of tools of social science inquiry (such as surveys, statistics, maps, documents)


Kansas Standards

Benchmark 1: The student uses a working knowledge and understanding of individuals, groups, ideas, developments, and turning points in the era of the emergence of the modern United States (1890-1930).

6. (A) analyzes the reasons for and impact of the United States’ entrance into World War I.

Benchmark 5: The student engages in historical thinking skills.

1. (A) analyzes a theme in United States history to explain patterns of continuity and change over time.

2. (A) develops historical questions on a specific topic in United States history and analyzes the evidence in primary source documents to speculate on the answers.

Fully describe the activity or assignment in detail. What will both the teacher and the students do?

Background: By 1917, the First World War had been raging for three years and the outcome seemed uncertain. The main belligerents were, on one side, the German and Austro-Hungarian Empires (the ’Central Powers’) and, on the other, the British, French and Russian Empires (the ’Entente’ or ’Allies’).  Despite American frustration and outrage over the “rape of Belgium” and German submarine warfare, including the sinking of the British passenger liner The Lusitania, the United States, much to the disappointment of the Allies, remained a neutral country.  What would it take to bring her into this stalemated conflict?

British Naval Intelligence and Cryptanalysis: Early in the war, British Naval Intelligence sought the help of Sir Alfred Ewing, an amateur cryptanalyst, to crack secret German codes. Ewing then enlisted the help of others he believed to be gifted at solving puzzles.  In time, the British cryptanalysts managed to break several key German codes thus making Room 40, where they were housed, the most efficient code breaking establishment in the world. Great Britain’s ability to decipher German coded messages being sent during WWI has proved invaluable for British intelligence allowing them to respond to German movements as necessary. However, the information gained must be used sparingly, for should Germany grow suspicious and change codes, British intelligence could suffer a setback that could adversely affect the outcome of the war.

Your Role:  You are one of Great Britain’s most highly prized intelligence experts and chief naval officer in charge of Room 40. Your job is to oversee the deciphering of codes and make strategic recommendations.  On the morning of January 16, 1917, Room 40 received a German message intercepted on the Swedish Roundabout (neutral Sweden’s telegraphic link with the United States). The skilled staff immediately recognized the code and set to work deciphering the message. (See ARC documents: 302025 & 302024)   A few hours later, an identical coded message was obtained from the United States cable.  Both messages were addressed to German Ambassador to Washington, Johann Heinrich von Bernstorff and contained a secret message from the German Foreign Secretary Arthur Zimmermann which was to be recoded and sent to Eckhardt, the German Ambassador to Mexico. When enough of the telegram was deciphered it revealed political dynamite—Your job is to examine the decoded message and determine the best way to handle this potentially explosive information and act accordingly.  (See ARC document: 302022)


The Zimmerman telegram appears to be the evidence needed to bring the United States into the war and save the beleaguered Allies. Select your course of action.

Course of Action # 1

Immediately reveal the Zimmermann telegram to the United States


  • The Swedes, whose cable Room 40 was not to read, would be deeply angered.
  • The Americans, whose cable Room 40 was not to read, would be deeply angered.
  • Germany would be keenly aware that the British had cracked the code and would stop using it resulting in a serious intelligence setback for the British.
  • The Americans might dismiss the telegram as British propaganda aimed at bringing the United States into the war.

Course of Action # 2

Keep the information a British intelligence secret


  • The Swedes and Americans will have no idea that messages sent on their telegraphic links are being decoded by the British. 
  • Germany will continue to use the code because they will remain unaware that it has been broken by the British. 
  • The Allies who are in desperate need of vital American aide will have to wait for unrestricted submarine warfare to draw the United States into the conflict.

Course of Action # 3

Wait and see if the Feb 1, start of unrestricted German submarine warfare brings the United States into the conflict. While waiting, perfect the translation of the Zimmerman telegram. The delay would also allow British intelligence time to contact an agent in Mexico City and try to obtain a copy of the actual Western Union telegraph sent to German Ambassador to Mexico Eckhardt. Such a copy, if obtained, could be revealed as the source of the information thus protecting the efforts of Room 40. Such a copy would also help prove that the telegram was legitimate and not mere propaganda. If America fails to enter the war quickly the Zimmermann telegram should then be revealed in the hope that it brings the United States into the war.


  • The Swedes and Americans will not know that their telegraphic links are being decoded by the British.
  • Germany will think that the telegram had been lifted from Eckhardt’s office.  They will continue to use the code because they will remain unaware that it has been broken by the British.
  • The Allies who are in desperate need of vital American aide will have to wait and see if unrestricted submarine warfare draws the United States into the conflict, if not hope that the revelation of the Zimmerman telegram will finally draw the US into the war. However, many Americans may remain suspicious that the telegram is nothing more than British propaganda.

Select your course of action:    #_____





Based on the course of action you selected, predict whether of not the United States will enter WWI.  If you believe that America will join the war how long do you think it will take?




How did your decision on how to handle the Zimmermann telegram compare with history?  Examine the documents and discuss your findings (ARC documents: 302022, 302023, & 187110)














How did the release of the Zimmermann telegram affect the United States?  Examine the following political cartoon and answer the questions below.



The Dallas Morning News, 2 March 1917.


Political Cartoon Questions:


  1. Describe in detail how Germany is depicted in the above cartoon?



  1. Describe how Mexico is depicted?


  1. Where do you think this cartoon is set?



  1. What is being offered?



  1. Why do you think such an offer was being made?



  1. What do you think the American reaction was to the offer?



Read and discuss Woodrow Wilson’s April 2, 1917 Address to Congress: (

Online Collection