A century after the fact, we have to reflect on the German declaration of unrestricted submarine warfare on 18 February 1915, and the British official release of the Zimmerman Telegram text to the United States on 23 February 1917 two years and five days later as little more than a coincidence. At the time it was little remarked on, but still it gives pause, and raises a question: what joins these two events?
The answer is American relations with Germany. By the end of 1914, it was clear to German planners that their earlier calculations for army planning and fleet building were based on gross miscalculations. The army was too small to fight France (and its colonies), Russia and the British Empire all at once, and once Belgium was added the ground manpower advantage was nearly 3:1 against Germany. Their long-dead architect of the “beat France, then Russia” motto of German strategic thinking, Alfred Von Schlieffen, would have been aghast at Helmuth von Molke’s dilution of the first offensives of 1914, and the arrival of a strong BEF at the frontiers had been, in his time, impossible to predict.
Worse, Alfred Von Tirpiz’ “risk fleet” theory that kept the German fleet just large enough to worry but not (theoretically) threaten Britain depended on a Royal Navy close blockade of the European coasts, so that the occasional German sortie could thin them out. But, this didn’t happen. This meant that German warships would always be outnumbered, and that the distant blockade of Europe, from the outset, was more effective at denying Germany vital foodstuffs and raw war materials. While Europe could withstand a protracted war, Germany could not, either by design or by temperament.
But Britain was also dependent on food and raw materials from overseas. In declaring that her submarines would no longer be bound by “cruiser” rules, Germany expected to be able to warn neutrals off of carrying cargoes to Britain, and to sink enough imperial shipping to bring Britain to the conference table with more sensible demands. Though some Germans, notably Chancellor Theobald von Bethmann Hollweg, also felt that such a move would antagonize the United States, the risk was worth the gain…if it worked.
Unfortunately, a lucky shot on 7 May 1917 brought forth the very worst in the Americans. Off Old Kinsale Head, Lusitania caught a torpedo from U-20 and sank, killing over a thousand people, including over a hundred Americans. Germany had promised it would observe cruiser rules in regard to the fast liners; in turn, Lusitania was listed on the German identification books as a merchant cruiser or troopship (which she was to become had she survived). Who was at fault here?
The American public and President Woodrow Wilson said Germany was. After the sinking of Arabic with the loss of three American lives on 15 August 1915, the German government demanded that submarines observe cruiser rules with all ocean liners, and on 18 September the Imperial High Seas Fleet withdrew the submarines from commerce warfare.
American rage over policies “worse than piracy” lingered, for the most part, until Germany declared unrestricted submarine warfare again on 1 January 1917. But shortly afterwards, the Americans and British, at about the same time, became aware of a German plot to involve Mexico in a war against the United States. The German Foreign Secretary, Arthur Zimmerman, transmitted a telegram to the ambassador from Germany, Heinrich von Eckardt, In it, Zimmerman mentioned a plan for Mexico to go to war against the United States, with German help, so that they could reacquire lands that the Americans had won in the Mexican War four generations before. On 23 February 1917, the British Foreign Minister, Arthur Balfour, delivered the text to the American ambassador to Great Britain, Walter Page.
It has been claimed that a precursor to the National Security Agency had already intercepted the cable (sent through a diplomatic wire via New York) and was waiting for the British to say something official. In the shadowy worlds of signals intercept and wartime diplomacy, this is credible. But the reaction to the content, when released to the public on 28 February, was nothing short of astounding. Germany at first denied it, but finally admitted that the message was genuine. But it had all the international credibility and validity of a treaty scribbled on a cocktail napkin. Nothing was settled, Mexico had no knowledge of the overture and had not solicited any such alliance or agreement. But the die was cast, and the road to war for America was, from that time onward, short.