German government felt that Americans

The German government felt that Americans had been fairly warned about the risks they assumed if they traveled on ships carrying arms and other materials to the Allies. Germany actually took out ads in U.S. newspapers warning Americans that they might be subject to submarine attacks under those circumstances. The Lusitania did have over 4 million rounds of ammunition as part of its cargo.

Was the sinking of this passenger ship a justified action? Why or why not? Be sure to justify your answer with evidence.