Sussex pledge

The Sussex pledge was a promise made in 1916 during World War I by Germany to the United States prior to the latter's entry into the war. Early in 1916, Germany had instituted a policy of unrestricted submarine warfare, allowing armed merchant ships – but not passenger ships – to be torpedoed without warning. Despite this avowed restriction, a French cross-channel passenger ferry, the Sussex, was torpedoed without warning on March 24, 1916; the ship was severely damaged and about 50 lives were lost. Although no U.S. citizens were killed in this attack, it prompted President Woodrow Wilson to declare that if Germany were to continue this practice, the United States would break diplomatic relations with Germany. Fearing the entry of the United States into World War I, Germany attempted to appease the United States by issuing, on May 4, 1916, the Sussex pledge, which promised a change in Germany’s naval warfare policy. The primary elements of this undertaking were:
 * Passenger ships would not be targeted;
 * Merchant ships would not be sunk until the presence of weapons had been established, if necessary by a search of the ship;
 * Merchant ships would not be sunk without provision for the safety of passengers and crew.

In 1917 Germany became convinced they could defeat the Allied Forces by instituting unrestricted submarine warfare before the United States could enter the war. The Sussex pledge was therefore rescinded in January 1917, thereby initiating the decisive stage of the so-called First Battle of the Atlantic. The resumption of unrestricted submarine warfare and the Zimmerman Telegram caused the United States to declare war on Germany on April 6, 1917.