I hope your talking about WW1
No, Germany was not justified in attacking U.S. merchant and passenger ships during World War I. The attacks on American ships were part of Germany's unrestricted submarine warfare campaign, which aimed to sink all ships that entered the war zone around the British Isles, including neutral vessels. This campaign was a violation of international law, as Germany had agreed to abide by the rules of naval warfare established by the Hague Convention of 1907, which required belligerents to provide for the safety of non-combatant ships and passengers.
Germany's attacks on American ships ultimately contributed to the United States entering World War I on the side of the Allies in April 1917. President Woodrow Wilson had initially pursued a policy of neutrality, but the attacks on American ships, as well as Germany's attempts to encourage Mexico to join the war against the United States, led to a shift in public opinion and a declaration of war.
In conclusion, Germany's attacks on U.S. merchant and passenger ships were not justified and were a violation of international law. The resulting entry of the United States into the war was a significant turning point in World War I.