The historic event that occurred on December 7, 1941, prompting U.S. entry into WWII, was the surprise military attack by Japan on the U.S. naval base at Pearl Harbor in Hawaii. This assault led to significant losses in naval vessels and personnel, shocking the American public and prompting an immediate response. Just a day later, President Franklin D. Roosevelt asked Congress for a declaration of war against Japan, famously calling it "a date which will live in infamy." This event marked a turning point, as the United States shifted from isolationism to active involvement in both the Pacific and European theaters of the war.