The attack on Pearl Harbor occurred on the morning of 7 December 1941 when the Imperial Japanese Navy launched a surprise air attack against American military facilities at Pearl Harbor in Hawaii. Pearl Harbor was the principal base of the United States Pacific Fleet and contained battleships, cruisers, destroyers, submarines, aircraft and extensive naval infrastructure. The Japanese strike force had approached Hawaii across the northern Pacific while maintaining radio silence. It consisted principally of aircraft carriers and their supporting vessels.
Japanese aircraft launched in two major waves. The first wave attacked shortly after 7.45 in the morning local time, while the second wave followed later. The attack targeted American battleships and airfields as well as other military installations. The United States suffered 3,435 casualties according to National Archives figures, while 188 American aircraft were destroyed or severely damaged and numerous ships were sunk or damaged.
The first Japanese wave achieved tactical surprise because American forces had not expected an attack of this scale at Pearl Harbor that morning. Japanese aircraft attacked from several directions, striking ships in the harbour and military airfields around Oahu. American aircraft were particularly vulnerable because many had been parked closely together, partly to reduce the risk of sabotage. This arrangement made them easier targets for Japanese aircraft.
Battleships became the most visible targets because they represented the traditional concentration of American naval power. Japanese aircraft used torpedoes adapted for the shallow waters of Pearl Harbor as well as high explosive and armour piercing bombs. The attack demonstrated the increasing importance of carrier based air power and showed that aircraft could inflict devastating damage on major warships even when those ships were inside a supposedly secure naval base.
Several American battleships were badly damaged or sunk. USS Arizona suffered a catastrophic explosion after an ammunition magazine was detonated, killing more than 1,000 members of its crew. The ship became one of the most enduring symbols of the attack and remains at the site beneath the USS Arizona Memorial. USS Oklahoma capsized after being struck repeatedly by torpedoes, trapping many sailors inside the hull.
Other battleships, including West Virginia, California and Nevada, were sunk or heavily damaged but were subsequently repaired in many cases. The Japanese attack therefore caused severe short term damage to the American battleship force. However, the Japanese did not completely destroy American naval capabilities at Pearl Harbor. Several important ships were absent, particularly the Pacific Fleet's aircraft carriers, which were at sea when the attack occurred.
American airfields were also attacked. Japanese aircraft struck facilities associated with the United States Army Air Forces and the US Navy, destroying or damaging large numbers of aircraft on the ground. The attack reduced American air power on Oahu and complicated the immediate response. American personnel attempted to resist with anti aircraft fire and whatever aircraft could be launched, but the initial Japanese advantage was overwhelming.
The Japanese operation was designed to achieve surprise and prevent American aircraft from interfering with the strike force. The destruction of aircraft on the ground was therefore an important component of the operation. Nevertheless, the survival of runways, fuel facilities and repair infrastructure was crucial because the Americans were able to restore operations and continue using Hawaii as a major base.
The second Japanese wave concentrated on additional ships, airfields and military installations. By the time it ended, the Japanese had inflicted enormous damage but had also suffered losses of their own. Japan lost 29 aircraft and several midget submarines, while fewer than 100 Japanese personnel were killed according to the National Archives summary. The Japanese strike force then withdrew before American forces could mount a major counterattack against the carriers.
This was an important feature of the operation because the Japanese aircraft carriers themselves remained outside the harbour and were not attacked by American aircraft. The absence of the American carriers became strategically important during the following months because carrier aviation rather than battleships became central to the Pacific naval war.
The attack had immediate political consequences. President Roosevelt addressed Congress on 8 December 1941 and requested a declaration of war against Japan. Congress approved the declaration, bringing the United States formally into the war against Japan. Germany and Italy subsequently declared war on the United States on 11 December, and the United States responded with declarations of war against Germany and Italy. The Pearl Harbor attack therefore transformed the war from a conflict in which the United States had provided substantial support to the Allies while remaining formally outside the European war into a conflict in which American armed forces directly participated on a global scale.
Pearl Harbor also generated major questions about American preparedness and intelligence. The United States had intercepted and decoded some Japanese diplomatic communications, and American commanders knew that relations with Japan were extremely dangerous, but the information available before the attack did not provide a complete and timely tactical warning of the exact target and time. Military intelligence, command structures and communications all became subjects of investigation after the disaster.
In the years after the war, congressional investigators examined whether failures of intelligence and command contributed to the attack's success. The National Archives notes that Congress later established a Joint Committee to investigate the circumstances before and after Pearl Harbor and to determine whether American shortcomings contributed to the disaster.
Pearl Harbor was therefore both a major tactical Japanese victory and a profound strategic turning point. Japan temporarily damaged American naval strength and achieved the surprise necessary for its wider offensive, but it did not destroy the American aircraft carrier force, submarine force, fuel reserves or industrial capacity. The United States rapidly mobilised its enormous economic resources for war. American shipyards produced new carriers, battleships, cruisers, destroyers and transport vessels while aircraft factories expanded on an unprecedented scale.
The attack also unified American public opinion around the war. The event consequently illustrates an important distinction between tactical success and strategic success. Japan achieved the first but failed to achieve the second, and Pearl Harbor became the immediate starting point of America's direct military participation in the Pacific War.
