December 7, 1941 was a "date which will live in infamy," according to Franklin Delano Roosevelt. The surprise attack on Pearl Harbor by the Japanese led the United States to enter World War II. 


  • On the morning of December 7, 1941, Japan attacked the US naval base at Pearl Harbor, Hawaii.
  • The surprise attack by some 350 Japanese aircraft sunk or badly damaged eighteen US naval vessels, including eight battleships, destroyed or damaged 300 US aircraft, and killed 2,403 men.
  • Across the nation, Americans were stunned, shocked, and angered. The attack turned US public opinion in favor of entering the Second World War. The United States declared war on Japan on December 8, 1941.
  • Japan’s allies, Germany and Italy, declared war on the United States on December 11. The United States responded in kind, and therefore entered World War II.

The Pearl Harbor attack

The Japanese surprise attack on Pearl Harbor began just before 8 a.m. local time Sunday morning, December 7, 1941. For over an hour, in two waves, some 350 Japanese aircraft—having taken off from six aircraft carriers 230 miles north of Oahu—attacked the naval base. Japanese forces wreaked havoc on US naval vessels and on US aircraft on the island’s airfield.1^1 In all, 2,403 Americans, including 68 civilians, died in the attack. In comparison, Japan suffered relatively light causalities—it lost only 29 aircraft and a few mini-submarines.2^2
Photograph of USS Shaw exploding at Pearl Harbor, December 7, 1941.
The USS Shaw explodes during the attack on Pearl Harbor, December 7, 1941. Image courtesy National Archives.
The American people were shocked, bewildered, surprised, and angered by the attack. On December 8, President Roosevelt addressed a joint session of Congress in the Capitol, his words broadcast on radio to the nation: “Yesterday, December 7, 1941—a date which will live in infamy—the United States of America was suddenly and deliberately attacked by naval and air forces of the Empire of Japan.”3^3
In his address, Roosevelt asked Congress to declare war against Japan, which it did that day. Three days later, Japan’s allies Germany and Italy declared war on the United States, and Congress reciprocated the same day. All previous domestic opposition to US entry into the war ceased. The United States was now immersed in a war it would conduct simultaneously in Europe and the Pacific.

Motive for the attack

The Japanese government decided to attack Pearl Harbor after the United States cut off US oil exports to Japan in the summer of 1941. Japan relied on the United States for eighty percent of its oil, and without US oil supplies its navy would be unable to function. In attacking Pearl Harbor the Japanese hoped to cripple or destroy the US Pacific fleet so that the Japanese navy would have free reign in the Pacific.4^4
Japan was also motivated strategically by ideas of creating an Asian co-prosperity sphere—“Asia for Asians”—in which Japan would take over the Asian colonial holdings of Europe and the United States. With the British, French, and Dutch caught up in the war in Europe, the Japanese believed the European powers would be unable to defend their Asian colonial holdings. Indeed, in the eight hours following the Pearl Harbor attack, Japan also attacked British-held Singapore, Hong Kong, and Malaya, and the US territorial possessions of the Philippines, Guam, and Wake Island.5^5

Forewarnings about the attack

The United States was caught unprepared for the attack on Pearl Harbor, but things might have turned out differently were it not for some bad luck. The United States had broken the Japanese diplomatic code in project “Magic,” and General George Marshall, having been handed a decoded Japanese message on the very day of the attack, had sent word to the US base at Pearl Harbor prior to the assault to “be on the alert.” Atmospheric conditions delayed transmission of Marshall’s message, and it did not arrive until after the attack.6^6
Moreover, the United States had known that a Japanese attack was imminent somewhere in the Pacific, but US military and government personnel had thought the Philippines or some other area of the South Pacific closer to Japan was the likely target. Pearl Harbor was 3,500 miles from Japan and had seemed to the US government and military an unlikely target.7^7
After Pearl Harbor, the United States rapidly mobilized for World War II.

What do you think?

What motives did Japan have in attacking the US naval base at Pearl Harbor?
What was the American response to the Japanese attack?
Do you think the United States would have entered World War II if the Japanese had not bombed Pearl Harbor? Why or why not?
Article written by John Louis Recchiuti. This article is licensed under a CC-BY-NC-SA 4.0 license.
  1. On the attack at Pearl Harbor and the events surrounding it, see David M. Kennedy, Freedom from Fear: The American People in Depression and War, 1929-1945 (New York: Oxford University Press, 1999), 500-526; Gordon W. Prange, At Dawn We Slept: The Untold Story of Pearl Harbor (New York: McGraw-Hill, 1981), 499-504.
  2. Kennedy, Freedom from Fear, 521-522.
  3. Franklin D. Roosevelt, “Address to Congress Requesting a Declaration of War with Japan December 8, 1941." Courtesy the American Presidency Project.
  4. Kennedy, Freedom from Fear, 512.
  5. See James L. McClain, Japan: A Modern History (New York: W.W. Norton & Co., 2001), 470.
  6. Kennedy, Freedom from Fear, 519.
  7. Kennedy, Freedom from Fear, 517, 525.