According to Roosevelt is his "Fireside Chat #19", the effects of Japan's attack on Pearl Harbor were that many American warplanes were destroyed.
Pearl Harbor is a United States naval base near Honolulu, Hawaii. Pearl Harbor attack was perpetrated on December 7, 1941. It marked a surprise aerial attack on the U.S. naval base at Pearl Harbor on Oahu Island, Hawaii, by the Japanese that precipitated the entry of the United States into World War II.