The German submarine attacks were seen as viscous attacks against the US. The cartoonist represents the German submarine as a shark, showing that the Germans are viciously attacking the U.S. who are represented by a sunken boat.
This poster was used as propaganda during WW1 to convince people to ration food and to not be wasteful with how much they eat and how much they make. By doing this you would be helping our American soldiers defeat the Kaiser and his U-boats.This made people think that the little things that they do at home can help out the war effort and those people who are at the front lines.
This propaganda poster shows a German soldier/Kaiser with a bloody sword that represents a German U-boat tearing through the ocean that is filled with dead people ( the American victims who were killed on the Lusitania). This poster also reads "ONLY THE NAVY CAN STOP THIS" meaning if you want to stop the sinking of American ships by German U-boats and stop the Germans in general than you need to join the Navy or the military at least, again trying to recruit for the war by inspiring the people.
This cartoon shows a German U-boat looking at an American boat which was not involved in the war yet. The American boat says Lusitania on the front of it showing that it is about to be sunk because that is what happened to it. On the boat shows John Bull who is using the American Flag for protection because he doesn't want the weapons that are being brought over to Britain to be destroyed.