Admiral Isoroku Yamamoto, Commander-In-Chief of Japan's Combined Fleet, had to be careful of his country's position in the Pacific. If he concentrated his forces too much in the Pacific Islands, then the mainland would be more susceptible to attack from Europe and even the United States. Yamamoto devised a plan that involved an opening blow to the United States Pacific Fleet at the same time as their offensive against British, American, and Dutch forces in Southeast Asia. He planned to cripple the United States while he quickly conquered much of Southeast Asia and gathered their natural resources. He hoped that his attack against the Pacific Fleet would demoralize the American forces and get them to sign a peace settlement allowing Japan to remain as the power in the Pacific. A month after the British attack on Taranto harbor, Yamamoto decided that if war with the United States was unavoidable he would launch a carrier attack on Pearl Harbor. In January of 1941, Yamamoto first began to commit to this strategy by planning out his attack and showing it to other Japanese officials.

Yamamoto developed the following eight guidelines for the attack:

(1) Surprise was crucial.
(2) American aircraft carriers there should be the primary targets.
(3) U.S. aircraft there must be destroyed to prevent aerial opposition.
(4) All Japanese aircraft carriers available should be used.
(5) All types of bombing should be used in the attack.
(6) A strong fighter element should be included in the attack to provide air cover for the fleet.
(7) Refueling at sea would be necessary, and
(8) A daylight attack promised best results, especially in the sunrise hours.

Many of Japan's Navy General Staff were in opposition to Yamamoto's plan, but they continued to prepare for the attack. All of the necessary training was given to troops, and all of the fighters and submarines were prepared. On December 6, 1941, President Roosevelt made an appeal for peace to the Emperor Hirohito of Japan. Not until late that day did the U.S. decode thirteen parts of a fourteen part message that presented the possibility of a Japanese attack. Approximately 9:00 a.m.(Washington time) on December 7,1941, the last part of the fourteen part message was decoded stating a severance of ties with the United States. An hour later, a message from Japan was decoded as instructing the Japanese embassy to deliver the fourteen part message at 1:00 p.m. (Washington time.) The U.S., upon receiving this message sent a commercial telegraph to Pearl Harbor because radio communication had been down.

At 6:00 a.m.(Hawaiian time) on December 7,1941, the first Japanese attack fleet of 183 planes took off from aircraft carriers 230 miles north of Oahu. At 7:02 a.m., two Army operators at a radar station on Oahu's north shore picked up Japanese fighters approaching on radar. They contacted a junior officer who disregarded their sighting, thinking that it was B-17 bombers from the United States west coast. The first Japanese bomb was dropped at 7:55 a.m. on Wheeler Field, eight miles from Pearl Harbor. The crews at Pearl Harbor were on the decks of their ships for morning colors and the singing of The Star-Spangled Banner. Even though the band was interrupted in their song by Japanese planes gunfire, the crews did not move until the last note was sung. The telegraph from Washington had been too late. It arrived at headquarters in Oahu around noon (Hawaiian time), four long hours after the first bombs were dropped.