Blockade of Germany
Under military pressure on Germany early in 1917, the Kaiser declared full unrestricted submarine warfare once more. Some German diplomats believed that the Americans would avoid war at all costs, and if not, germany could hopefully Germany bring Britain to its knees before American power made much difference in Europe. In February, 86 vessels were sunk, followed by 103 in March and then 155 in April. The US finally declared war on Germany in April 1917 after the Zimmermann Telegram. The Americans and the British together later defeated the U-boats.