Pearl Harbor Remembrance Day.
Sixty-two years ago today, on 7 December 1941, the US naval base at Pearl Harbor, on the island of Oahu, in the territory–later the state–of Hawaii, was attacked without warning by the Empire of Japan. (*) Over 2,400 Americans were killed. (†) (‡) Afterward, some Americans were trapped inside battleships, only to slowly starve to death because they could not be freed. (§)
After that day of infamy, the US entered World War II, and the course of history was changed forever.
Update: 3 March 2004. The White House proclamation. (**)