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Germany’s decision in January 1917 to resume unrestricted submarine warfare, thus bringing the United States into World War I, is unquestionably one of the most important events in 20th century military history. Unlike Adolf Hitler’s declaration of war on the United States on Dec. 11, 1941—an act of obvious lunacy—Germany’s move to unleash its submarines in 1917 seemed at first a calculated risk that might win the war for the Central Powers before the United States could tip the scales in favor of the Triple Entente.

German U-boats were not necessarily the instruments of a carefully calculated strategy, however. Instead, their depredations on neutral merchant shipping served notice to the world that the nature of the war had undergone a fundamental shift in politics, war aims and technology. After this, there would be no turning back. The war had become a fight to the finish.

A few months earlier, in the autumn of 1916, it seemed the war might end in a negotiated peace. The bloodbaths at Verdun and the Somme had convinced politicians on both sides that further fighting would only bring Europe to ruin. In December German Chancellor Theobald von Bethmann-Hollweg put out tentative peace feelers, and President Woodrow Wilson asked both sides for statements on war aims as a precursor to negotiation.

Unfortunately, democracy in Germany was on its last legs. Bethmann-Hollweg, who had steadfastly opposed unrestricted submarine warfare, had become isolated. Frustrated by growing hardships caused by the British blockade, Germans became more supportive of military rule and ruthless war aims. German generals angrily rejected peace initiatives and openly despised the chancellor. They overthrew moderate Foreign Minister Gottlieb von Jagow and named the belligerent Arthur Zimmerman as his replacement. They withdrew peace feelers to the Entente and silenced other critics.

German military leaders also became increasingly confident that total military victory lay within their grasp. Massive triumphs in the Balkans and the rollback of the last-gasp Brusilov Offensive had convinced them that Eastern Europe, including Russia, was ripe for conquest. German war aims, which had been relatively moderate in 1914, expanded into visions of a vast new “Greater Germany” in the east.

On the Western Front prospects for a German land victory seemed remote. The stalemate in France and Belgium was total. New technology, however, seemed to offer a way out. At the beginning of the war Germany had only 28 operational U-boats. Moreover, submarines were small, carried few torpedoes, could spend relatively little time underwater and had a limited cruising range. In short, they were completely inadequate for establishing a blockade of Great Britain. That is one of the reasons Germany, in the wake of its May 7, 1915, sinking of RMS Lusitania, acquiesced to Wilson’s demands to restrict submarine targets to belligerent vessels, sparing passenger liners and neutral merchant ships.

By early 1917, however, Germany had nearly tripled its fleet of U-boats from the previous year. More important, its submarines were larger, carried 12 torpedoes, and could cruise farther and spend more time underwater. They also carried new armaments, such as deck guns and explosive charges with which to finish off enemy ships. With these new U-boats at hand and many more under production, High Seas Fleet Admiral Reinhard Scheer proclaimed he had the tools to starve Britain into submission and win the war.

Field Marshal Paul von Hindenburg, chief of the General Staff, and his deputy, Maj. Gen. Erich Ludendorff, agreed with Scheer the time had come to end restrictions on submarine warfare. A “U-boat movement” of intellectuals, businessmen and right-wing politicians lobbied for the same cause in the Reichstag. On Jan. 8, 1917, German military and naval representatives met with the kaiser and brought him around to their point of view. Bethmann-Hollweg was not even invited to the meeting. Germany, by now essentially ruled by a military dictatorship, prepared for a new war in which the only options were total victory or total defeat.

On April 6, 1917, in response to the resumption of unrestricted submarine warfare and other provocations, the United States declared war on Germany. While more than a year would pass before American ground forces had an impact on fighting on the Western Front, the economic boon of American intervention was immediate, as a massive infusion of American dollars helped prop up the tottering French and British economies. The submarine blockade, meanwhile, got off to a strong start but eventually withered, thanks to the convoy system and vigorous antisubmarine measures. With the end of the U-boat menace, Germany’s defeat became only a matter of time.


Originally published in the January 2012 issue of Military History. To subscribe, click here.