一九一七年,第一次世界大战交战双方陷入艰苦的阵地战已经两年了。协约国和同盟国在战场上都未能取得进展。英国人企图实行海上封锁,困死德国人。德国人则企图以潜艇战来切断英国的供给线。在东部战场,虽然俄国人的抵抗减弱了,但美国对协约国的援助却日益加强。此时,德国人别无出路,唯一的就是必须把协约国的所有供应舰船击沉。但这样一来,有可能会引起美国参战。为了避免这一点,德国外交部长阿瑟尔 In 1917, it was two years since the warring parties of the First World War got into a strenuous battle. Allies and allies failed to make progress on the battlefield. The British tried to impose a sea blockade and sleepy Germans. Germans attempt to cut off the UK supply line by submarine warfare. In the eastern battlefield, although the resistance of the Russians has weakened, the U.S. assistance to the Allies has been steadily increasing. At this point, the Germans have no other way out, the only thing is that all the supply ships of the Allies must be sunk. But this way, it may cause the United States to enter the war. To avoid this, German Foreign Minister Asssel