When Did Pearl Harbor Happen?

Japan attacks Pearl HarborOn December 7, 1941, a date that President Franklin D. Roosevelt claimed would “live in infamy,” the Imperial Japanese Navy conducted a surprise aerial assault on Pearl Harbor. This unprovoked attack brought the United States into World War II, as it immediately declared war on Japan.

Pearl Harbor was, and still is, the most important American naval base in the Pacific and home to the US Pacific Fleet. It is located on the Hawaiian island of Oahu.

Background: Why did the Attack on Pearl Harbor Happen?

Japanese Territorial Expansion in the 1930s

Since the 1930s, the Japanese government had increasingly come under the influence of right-wing military leaders seeking to create a larger Japanese empire on the Pacific Rim. The United States, the United Kingdom, the Soviet Union, and the Republic of China, represented significant obstacles to this expansion.

Japanese aggression began with the seizure of Manchuria from China in September 1931. The following year, this conquered territory was transformed into a Japanese puppet state, Manchukuo (1932–1945), under the nominal leadership of the last emperor of China, Pu Yi. The League of Nations carried out an investigation of the incident and concluded that Japan had, without a declaration of war, forcibly seized and occupied a large section of Chinese territory. It urged Japanese troops to withdraw from the occupied lands. In response, Japan withdrew from the League of Nations in March 1933. Neither the League of Nations nor the United States recognized the allegedly independent state.

Japan Builds up its Military and Joins the Axis Powers

In the mid-1930s, the Japanese military began to exert more authority in foreign and domestic policy. Japan withdrew from participation in international naval conferences that had limited the size of the country's fleet. Naval construction dramatically increased so that the Japanese possessed the third largest navy in the world by 1941. In the Pacific, the Japanese navy surpassed the combined power of the British and American fleets. The army rapidly expanded as well, doubling in size between 1936 and 1941.

During this time, Japan was also drawing closer to Nazi Germany and Fascist Italy. In November 1936, Japan signed the Anti-Comintern Pact. Then in September 1940, Germany, Italy, and Japan signed the Tripartite Pact. This pact formalized the alliance between the three countries. They were subsequently referred to as the Axis powers.

In July 1937 fighting erupted between Japanese and Chinese forces and escalated into a full-fledged war that lasted until 1945.

The United States Responds to Japanese Expansion

Japanese territorial aggression triggered widespread condemnation in the United States and elsewhere. On October 5, 1937, President Franklin D. Roosevelt warned that the “very foundations of civilization” were being “seriously threatened.” Although he did not single out any particular nations, the warning aimed to raise American concerns about Japanese actions in China and German and Italian intervention in the Spanish Civil War. A “quarantine” was necessary to halt the spread of the “epidemic of world lawlessness.” Roosevelt feared that Japanese expansionism would not end in China, but spread to Hong Kong, Indochina, and the Philippines, representing a threat to the United States.

Although the League of Nations condemned Japan's actions in China, diplomatic efforts aimed at halting the fighting failed. Roosevelt considered a joint Anglo-American naval blockade of Japan, particularly in December 1937 after Japanese aircraft attacked and sank several American vessels, including the patrol boat, the USS Panay, as well as some British ships in China. Isolationism at home and appeasement abroad put an end to such efforts.

Following the outbreak of war on the European continent, Japan took advantage of the situation to occupy territory in Asia. After France's defeat by Nazi Germany, the Imperial Japanese government pressured the Vichy regime into cutting off military supplies to China from Indochina and then permitting the Japanese military to house its troops there. In fall 1940, the US government offered to provide the embattled Chinese republic with aircraft and loans, which were then followed by economic sanctions against Japan that banned the export of aviation gasoline and scrap metals, including iron and steel. In summer-fall 1941, the United States froze Japanese assets and placed an embargo on oil exports to Japan.

Planning for the Attack on Pearl Harbor

As US policy and sanctions became more aggressive, Japanese planners determined to attack American positions in the Pacific: specifically, the Philippines, Guam and Wake Islands, and the Pacific Fleet at Pearl Harbor.

The dilemma faced by Japanese planners was how to counter the greater American naval power and economic potential.

The plan that emerged called for a surprise attack that would destroy the entire US Pacific Fleet at Pearl Harbor, while at the same time eliminating the other US forward positions. The strategic goal was to so cripple US naval power in the Pacific that the United States would be unable to interfere with Japanese conquests.

Japanese planners hoped that by the time the United States had recovered and rearmed it would face an imposing defensive perimeter that it would be unable or unwilling to defeat. A large naval strike force set sail from Japan operating under strict radio silence and avoiding shipping lanes to escape detection.

What Day and Time Did the Attack on Pearl Harbor Take Place?


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At 7:55 am on December 7, 1941, the first of two waves of Japanese naval aircraft launched from six aircraft carriers attacked Pearl Harbor, catching US forces completely by surprise. Two thousand four hundred US sailors and soldiers were killed and 1,200 wounded. Well over half of the military aircraft were damaged or destroyed, almost all on the ground.

Of the US battleships present, all were hit and two, the Arizona and Oklahoma completely destroyed. Japanese air commanders requested a third strike, but Admiral Nagumo, in charge of the attacking force declined, preferring to avoid greater losses and presuming that the raid had been a success.

What were the Immediate Outcomes of the Attack on Pearl Harbor?

On its face, the attack on Pearl Harbor may indeed have seemed a brilliant strike. The US Pacific Fleet was effectively eliminated as an offensive force and would be unable to intervene in Japanese expansion for the foreseeable future. In addition, the attack had only cost 29 Japanese planes.

However, on closer inspection and in strategic terms, the assault was a failure for a number of reasons. First, the most important ships in the US fleet, the aircraft carriers, were away on maneuvers and not present during the attack. Second, US oil supplies, submarine fleet, and repair facilities remained undamaged. Third, while the all-important battleships had sustained heavy damage, all but two were eventually refloated, repaired, and returned to service. And finally, the attack galvanized a previously disinterested US public in support of the war.

Global Repercussions

The attack on Pearl Harbor had impacts far beyond Hawaii and the United States. Adolf Hitler applauded the attack and declared war on the United States even though the United States had only declared war against Japan. Before Pearl Harbor, many Americans maintained an isolationist stance and were reluctant to become involved in the war in Europe.

Hitler's declaration of war on the United States is seen by many historians as one of his greatest errors in judgment. In less than a year, American ground troops would be fighting German forces in North Africa. In addition, American materiel support of Nazi Germany's primary enemy, the Soviet Union, could proceed at full speed.

Pearl Harbor even had a small but identifiable impact on the Holocaust. The Wannsee Conference, whose goal was to coordinate the organizations responsible for the execution of the Final Solution, had originally been scheduled for 8 December. In light of the events of early December 1941, Reinhard Heydrich was forced to reschedule the meeting for 20 January 1942.