Although the Royal Navy’s Grand Fleet lost more tonnage than the Imperial High Seas Fleet at the Battle of Jutland, the Germans never sortied from port again. In response, they prepared for a policy of unrestricted submarine warfare to begin on 1 February 1917. If the Royal Navy couldn’t be beaten at sea then the country would be starved into surrendering. The sinking of the ocean liner RMS Lusitania in 1915 had almost brought the United States into the war on the Allied side; unrestricted submarine warfare in 1917 surely would. If the plan worked Britain would sue for peace before the US presence could make itself felt on the Western Front.

On 3 February 1917, the first victim of the new policy was spotted. U-53 stopped and boarded the cargo ship SS Housatonic off the southwestern tip of England. The Housatonic was sailing with a hull full of wheat from Galveston to Liverpool. The polite U boat captain ordered the ship abandoned then sank her with a single torpedo. He then towed the life boats toward shore and subsequently snuck away.

The Housatonic was the first of many ships sunk under unrestricted submarine warfare. The homely old steam freighter caused an uproar in the US Congress and inside the the Wilson Administration. President Wilson had just narrowly won the recent election on a platform of non intervention in the the war in Europe, even though he privately expressed his doubts that America could stay out of the war.
Great Britain knew it too, and was just waiting for the right time to inform America of a recent intelligence development. The sinking of the SS Housatronic provided the perfect opportunity.