Subsequent attacks

Later during the War several other, small-scale, attacks were also made on Pearl Harbor .

In March, 1942, in Operation K-1, a preparation for the Midway invasion, two Japanese H8K flying-boats, based at Wotje in the Marshall Islands, were tasked with reconnaissance to see how repairs were progressing, and to bomb the important "Ten-ten" repair dock. The distance involved required refueling en-route, and was done from submarines at French Frigate Shoals, 500 miles north-west of Pearl Harbor . Poor visibility hampered the mission, and the bombs were dropped some miles from their target.

Five Japanese submarines supported the operation: I-9 as a radio beacon; I-19, I-15 and the I-26 to refuel the flying boats and I-23 to provide weather reports. However, the I-23 was lost without trace.

American ships were posted to the Shoals thereafter, which precluded another attempt using the same approach.

Immediate aftermath
American response

President Franklin D. Roosevelt signed the Declaration of War against Japan on the day following the attack.

Ninety minutes before the attack on Pearl Harbor began (December 8, 1941 Japan time, on the other side of the international date line), Japanese troops invaded British Malaya. This was followed by an early morning attack on the New Territories of Hong Kong and within hours or days by attacks on the Philippines, Wake Island, and Thailand and by the sinking of HMS Prince of Wales and Repulse.

On December 8, 1941, the U.S. Congress declared war on Japan with Jeannette Rankin casting the only dissenting vote. The United States was outraged by the attack and by the late delivery of the note breaking off relations, actions which it considered treacherous. Roosevelt signed the declaration of war the same day, and called the previous day "a date which will live in infamy" in an address to a joint session of Congress. Continuing to intensify its military mobilization, the U.S. government began converting to a war economy.

The Pearl Harbor attack immediately galvanized a divided nation into action. Public opinion had been moving towards support for entering the War during 1941, but there was considerable opposition up till the Pearl Harbor attack. Overnight, Americans united against Japan , and that response probably made possible the unconditional surrender position taken by the Allied Powers. For that reason, some historians believe that the attack on Pearl Harbor doomed Japan to defeat simply because it awakened the "sleeping U.S. behemoth", regardless of whether the fuel depots or machine shops had been destroyed or even if the carriers had been caught in port and sunk. U.S. industrial and military capacity, once mobilized, was able to pour overwhelming resources into both the Pacific and Atlantic theaters.

The perception of the treacherous nature of the attack on Pearl Harbor also sparked fears of sabotage or espionage by Japanese Americans and was a factor in the subsequent Japanese internment in the western United States, and Roosevelt signed United States Executive Order 9066 requiring all Japanese Americans to show up for arrest and internment.

Nazi Germany and Fascist Italy declared war on the United States on December 11, four days after the Japanese attack. Hitler and Mussolini were under no obligation to do so under the terms of the mutual-defense terms of the Tripartite Pact. However, relations between the European Axis Powers and American leadership had gradually deteriorated since 1937. Earlier in 1941, the Nazis learned of the U.S military's contingency planning to get troops in Continental Europe by 1943; this was the "Rainbow Five" plan and was made public by sources unsympathetic to Roosevelt 's New Deal, notably the Chicago Tribune. Hitler seems to have decided that war with the United States was unavoidable, and the Pearl Harbor attack, the publication of the Rainbow Five plan, and Roosevelt's post-Pearl Harbor address, which focused on European affairs as well as the situation with Japan, probably contributed. Hitler also underestimated American military production capacity beyond Lend Lease, the nation's ability to fight on two fronts and the time Operation Barbarossa would require. Similarly, the Nazis may have hoped the declaration of war, a showing of solidarity with Japan , would result in closer collaboration with the Japanese in Eurasia . Regardless, the decision was an enormous strategic blunder and it enraged the American public. It allowed the United States to immediately enter the European theatre of war in support of the United Kingdom and the Allied camp without much public debate about the relative lack of retaliation against Japan. Conversely, the Pacific theatre became Japan's focus of attention; overwhelming the Americans—and later, defending against them—undermined cooperative efforts against British holdings from Southeast Asia to the Middle East. Opening a second front against the Soviet Union , which never came to fruition, also would have been of value to the combined Axis' war effort.

USS Utah took a torpedo hit and capsized early in the battle. The wreck remains at Pearl Harbor.

President Roosevelt appointed an investigating commission, headed by U.S. Supreme Court Justice Owen Roberts to report facts and findings with respect to the attack on Pearl Harbor. Both the Fleet commander, Rear Admiral Husband E. Kimmel, and the Army commander, Lieutenant General Walter Short (the Army Air Corps had been responsible for aerial defense of Hawaii, including Pearl Harbor , and for general defense of the islands against hostile attack), were relieved of their commands shortly thereafter. They were accused of  'dereliction of duty' by the Roberts Commission for not making reasonable defensive preparations. This evaluation has been controversial in some quarters ever since. On May 25, 1999, the Senate voted to recommend both officers be exonerated on all charges of dereliction of duty, citing allegations of the denial to Hawaii commanders of vital intelligence which was available in Washington.

In terms of its own objectives, the attack on Pearl Harbor was a tactical success which far exceeded the expectations of its planners. In execution, it has few parallels in the military history of any era. Even the surprise British carrier strike on the Italian's Taranto naval base in 1940 had not been so devastating in terms of damage inflicted, although in successfully neutralising the Italian navy it had much greater strategic implications. Due to its losses at Pearl Harbor and in the subsequent Japanese invasion of the Philippines, the U.S. Navy and Army Air Corps were unable to play any significant role in the Pacific War for the next six months. With the U.S. Pacific Fleet essentially out of the picture for the moment, Japan was temporarily free of worries about the rival Pacific naval power. It went on to conquer Southeast Asia, the Southwest Pacific, and to extend its reach far into the Indian Ocean.

Although Pearl Harbor was the most notable attack on American soil during WWII, there were several others.