Entitled: "Only the Navy can stop this". Poster showing a florid German soldier, wearing pirate skull and crossbones and brandishing a bloody sword as he wades in a tide of women's and children's bodies. United States Navy operations during WWI began on April 6, 1917, after the formal declaration of war on Germany. The American navy focused on countering enemy U-boats in the Atlantic Ocean and the Mediterranean Sea while convoying men and supplies to front lines in France and Italy. Because of United States' late entry into the war her capital ships never engaged the Germans and few decisive submarine actions occurred. Artist William Allen Rogers, 1917.