<P> The first American hostile action against Axis forces that resulted in physical destruction was on 14 September 1941, when USCGC Northland destroyed a German weather station in northeast Greenland . The action was based on an agreement with Danish Ambassador to the United States Henrik Kauffmann in April 1941 to patrol the Danish island . </P> <P> The first American - caused casualties occurred on 7 December 1941 when the USS Ward attacked and sank a Japanese midget submarine near the entrance to Pearl Harbor prior to the commencement of the Japanese air attack upon Hawaii later that day . As a result of the attack on Hawaii, America declared war on Japan on 8 December 1941 . Germany and Italy declared war on the United States three days later . </P> <P> The first planned offensive action by the United States in World War II came in January 1942 when the aircraft carrier USS Enterprise attacked Japanese bases in the Marshall Islands . </P>

Where did the us attack first in ww2