The British ship Lusitania is sunk by a German U-boat. Although the Lusitania was a passenger ship, it was carrying a supply of munitions. Germany had previously declared the waters around Great Britain were a war zone, and all merchant ships were legal targets. The 1,201 people who drowned in its sinking included 128 Americans. The incident prompted U.S. President Woodrow Wilson to send a strongly worded note to the German government demanding an end to German attacks against unarmed merchant ships. By September 1915, the German government had imposed such strict constraints on the operation of the nation’s submarines that the German navy was persuaded to suspend U-boat warfare altogether.