National Pearl Harbor Remembrance Day, also referred to as Pearl Harbor Remembrance Day or Pearl Harbor Day, is observed annually in the United States on December 7, to remember and honor the 2,403 Americans who were killed in the Japanese surprise attack on Pearl Harbor in Hawaii on December 7, 1941, which led to the United States declaring war on Japan the next day and thus entering World War II. On Pearl Harbor Day, the American flag should be flown at half-staff until sunset to honor those who died as a result of the attack on U.S. military forces in Hawaii. Pearl Harbor Day is not a federal holiday – government offices, schools, and businesses do not close. Source: National Pearl Harbor Remembrance Day & Collins Flags All flags flying with the US Flag should also be lowered. If you have a flag that cannot be lowered, respect for the day can be shown by tying a black cord or ribbon to the top of the mast.