The British code breaking triumph of January 1917

As World War I raged across Europe, the revolution that began in Mexico in 1910 continued to rip the country apart. The revolutionary forces commanded by the media savvy Francisco (Pancho) Villa controlled much of northern Mexico. As the military alliances of Mexico’s feuding political factions shifted, the fighting along the border raised apprehension in the United States. As conditions grew worse, American citizens living in Mexico were urged to leave. In January 1916, sixteen Americans were grabbed from a train near Santa Isabel and executed. In early March 1916, Villa attacked Columbus, New Mexico killing 10 civilians and eight U.S. soldiers. Two American civilians and six soldiers were wounded. The raiders burned much of the town, stealing horses and mules.

In a violation of Mexican sovereignty, an angry President Wilson sent Gen. John J. Pershing’s expedition into Mexico to hunt Villa down. Although they chased and routed Villa’s forces, they were never able to capture Villa. Somewhat disappointedly, Pershing’s force returned to the United States in February 1917. As the contending Mexican factions continued to jockey for power, the bad border security situation and the threat of war with Mexico often pushed the war news from Europe from the front pages of American newspapers.

At the time, America was edging closer to entering the war in Europe on the side of the nearly exhausted Allies. Between 1915 and 1917, the Allied Powers borrowed $2.5 billion from American bankers, 85 times the amount loaned to Germany. The British blockade of the ports of the Central Powers was proving effective, it cut off the trade of neutral nations with the enemy. Unrestricted submarine warfare had been a point of contention between the U.S. and Germany since the Lusitania had been sunk in May 1915. After a pause, Germany announced it would resume unrestricted submarine warfare in February 1917 in an effort to disrupt Allied supply lines.

In this edgy environment, Britain’s military code-breaking operatives provided America the jolt needed to abandon neutrality and join the Allied war effort. The British intelligence agents had secretly tapped into a cable relay station in England, gaining access to every message transmitted over America’s trans-Atlantic telegraph cable. The British military cryptographers were skilled, able to decode most of the coded cables sent by foreign governments. They were reading President Wilson’s communications and everything else that passed over the system.

America’s leaders lacked a clear understanding of what the British were doing because prior to the U.S. entry into the war, little thought had been given to communications security. There was no government agency capable of reading the secret diplomatic traffic and cipher telegrams of foreign governments. The War Department lacked the capacity to intercept and decode enemy military messages.

The British cryptographic analysts intercepted and decoded a diplomatic directive sent on January 19, 1917 from the German Foreign Office to the German Ambassador in Mexico. It instructed the ambassador to propose a military alliance between Germany and Mexico if America entered the war on the side of the Allies. Although financially stretched to the limit, Germany would provide Mexico with financial aid. In return for the military support, Mexico would be able to regain some of her lost territory, specifically the states of Texas, New Mexico and Arizona.

After devising a cover story on how the information was obtained, the British handed the text of the infamous “Zimmermann Telegram” to the American Ambassador in Britain on February 24. On March 1, the Wilson administration released it to the press. The publication triggered immediate public outrage, helping to boost popular support for the declaration of war on Germany. On April 6, 1917, Congress approved a resolution for war with the Central Powers.

In Mexico, the unsteady government of President Carranza mulled over the German military alliance proposal, deciding it was unworkable. Mexico declined the German offer on April 14. It was a major diplomatic flub on the part of Arthur Zimmermann, Germany’s Foreign Secretary. His ill-conceived attempt to tie down American troops in a war with Mexico had failed. The U.S. would provide the hard pressed Allies with the winning advantage as loans, war supplies and soldiers poured into Europe. The U.S. sent two million troops to France, 1.3 million would see combat. At the end of the war, American casualties totaled 320, 518. America’s emergence as a creditor nation was among the many unanticipated consequences brought by the war.