The Attack on Pearl Harbor: The Beginning of American Involvement in World War II

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: The European Theater in WWII: The Eastern Front, Western Front & Fight for North Africa

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:08 Japan Rivals the US
  • 2:02 Undeclared War
  • 4:07 Warning Signs
  • 6:01 December 7, 1941
  • 8:40 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Alexandra Lutz

Alexandra has taught students at every age level from pre-school through adult. She has a BSEd in English Education.

On December 7, 1941, the Empire of Japan launched a surprise attack against Allied possessions in the Pacific, including the American military base at Pearl Harbor, Hawaii. After decades of conflict between the two nations, the U.S. declared war.

Japan Rivals the U.S.

'Yesterday, December 7th, 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.'

But, to say it came as a complete shock would not be the whole story - the United States and Japan had been at odds for decades. First of all, just after the turn of the century, both nations were competing for political and economic influence throughout the Pacific. Then, after World War I, Japan laid claim to former German colonies in the East, expanding the Japanese Empire and emerging as a serious rival to America's position in Asia.

In 1922, the world's nine largest naval powers (including Japan and the United States) signed a series of treaties limiting warship capacity, agreeing to consult each other in any disputes over China and respecting the territorial integrity of that nation. But certain classes of ships weren't restricted by the Nine Power Treaty, leading to an arms race until the loopholes were closed.

Then, in 1931, Japan blatantly violated these agreements by invading Manchuria and other parts of China. With the Nine Power Treaty now broken, America increased its naval power in the Pacific and several nations began funneling aid to China through their colonies in Asia.

Undeclared War

Continued Japanese aggression for the next decade, including the invasion of China in 1937, their alliance with the Axis powers of World War II and the invasion of French Indochina resulted in escalating American involvement without a declaration of war. Concerned American pilots formed an independent air force called the Flying Tigers and worked with the Chinese government to prepare defenses over that nation's airspace. The U.S. government also joined its allies in seizing Japanese assets and placed embargoes on steel, oil and other raw materials needed for war production.

Running short on supplies, Japan had two choices: submit to foreign demands by abandoning the invasion of China or seize the resources it needed by attacking even more territory. Japan chose the latter. With the European powers already embroiled in World War II, it looked like the only thing standing in Japan's way of controlling the entire Pacific Rim was the United States.

The Empire of Japan devised an elaborate plan to simultaneously attack Allied territories throughout the Pacific, including Hawaii, the Philippines, Wake Island, Guam, Malaya, Thailand, Hong Kong and Midway. In one sweep, they could secure desperately needed resources, discourage foreign interference and cripple America's increasing military strength in the Pacific.

To Pearl Harbor alone, Japan sent 30 ships, including 6 aircraft carriers. There was a separate force of submarines tasked with sinking any American ships that might escape the harbor. The top-secret Japanese fleet set sail on November 26, 1941, and by avoiding shipping lanes, moved into position without being spotted.

Warning Signs

Although the Allies had not yet broken the Japanese naval encryption code, there were suggestions of an impending attack. Beginning as early as January 1941 and periodically throughout the year, Washington sent warnings to fleet and field commanders in Hawaii, the Philippines, Alaska and the Panama Canal Zone. But many American decision-makers believed that Japan did not have the military capacity to pull off a major strike.

The day after the Japanese fleet embarked, a message went out to all Pacific stations reading, 'Consider this dispatch a war warning.' Many expected an attack on the Philippines to be most likely. However, minimal steps were taken in Hawaii. Most importantly, the aircraft carriers were all sent out, and in a fatal miscalculation, the Army commander lined up his planes as a protection against sabotage.

In order to achieve complete surprise, Japan violated international law and diplomatic protocol by attacking without first sending an ultimatum. Still, in the wee hours of December 7, 1941, there were at least three clues of imminent danger.

First, an American patrol spotted a submarine periscope as it followed a cargo ship through the anti-submarine nets into Pearl Harbor. A nearby destroyer, the USS Ward, fired at the mini-sub and sank it. Second, a radar operator noticed the incoming Japanese air force, but officers were expecting planes from California that morning and dismissed the sighting. Third, Washington forwarded credible intelligence of an attack, but it didn't reach the commander at Pearl Harbor until hours later.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account