At a war council in Pless Castle, German military leaders convinced the Kaiser that unrestricted U-boat attacks could starve Britain into surrender within months, before American intervention could matter. The decision, taking effect February 1, sank Allied and neutral shipping indiscriminately and became the single most direct provocation drawing the United States into declaring war that April.
German naval strategists, chiefly Admiral Henning von Holtzendorff, presented Wilhelm II with statistics claiming that sinking 600,000 tons of shipping per month would bring Britain to its knees in five to six months — comfortably before America could mobilize meaningfully. Chancellor Theobald von Bethmann-Hollweg, who feared American entry above all else, was overruled after months of resisting the same proposal.
The gamble unraveled almost immediately. Woodrow Wilson had already severed diplomatic relations with Germany the previous February over similar U-boat provocations, and the resumption in 1917, compounded by the intercepted Zimmermann Telegram proposing a German-Mexican alliance, pushed American public opinion decisively toward war.
By April 1917 the United States had declared war on Germany, bringing fresh troops, industrial capacity, and naval resources that tipped the exhausted stalemate of the Western Front. The submarine campaign did sink enormous tonnage — over 500,000 tons some months — but Britain adapted through convoy tactics, and the strategic bet that seemed decisive at Pless Castle ultimately hastened Germany's own defeat.
Key people: Kaiser Wilhelm II, Henning von Holtzendorff, Theobald von Bethmann-Hollweg