On Feb. 3, 1917, the United States broke off diplomatic relations with Germany, which had announced a policy of unrestricted submarine warfare, the same day an American cargo ship, the SS Housatonic, was sunk by a U-boat off Britain after the crew was allowed to board lifeboats. In 1867, Crown Prince Mutsuhito became Japan’s 122nd emperor at age 14 four days after the death of his father, Emperor Komei .