Pearl Harbor, Causes and Main Events 1919 – 1941

Pearl HarborThis timeline details the main causes and events of the Japanese attack on Pearl Harbor 1941

Please note: times shown are local times, where applicable Hawaii time has also been given.

1919 (4th May)
Paris Peace Conference
The Paris Peace Conference held at the end of World War One, had given German rights in China to Japan rather than allowing them to return to China. There were Chinese protests against this at the Gate of Heavenly Peace in Tiananmen Square, Peking (Beijing) but they had no affect. The settlement gave Japan a presence in China and a desire for more land there.
1931 (18th September)
Japan invaded Manchuria. China appealed to the League of Nations for support. Japan simply withdrew from the League meaning that sanctions would not apply.
1937 (7th July)
Second Sino-Japanese War
Japan invaded north China and took Peking (Beijing).
1937 (21st August)
Sino-Soviet Non-Aggression Pact
Russia and China signed this pact. As a result, the Soviet Union sent weapons and economic aid to help China fight the Japanese.
1937 (13th December)
Rape of Nanking
The Japanese took Nanking (Nanjing). The following six weeks saw Japanese soldiers murder Chinese inhabitants of the city, rape women and loot and pillage goods and supplies. The total number of Chinese killed is unknown but estimated to be between 40,000 and 300,000.
1939 (3rd September)
World War Two
Britain and France declared war on Germany after Nazi troops invaded Poland.
1939 (October)
The Chinese city of Changsha held out against an attack by Japan.
1940 (May)
Roosevelt moved the American fleet from California to Pearl Harbor, Hawaii. He believed that being 4,000 miles from Japan made it difficult for the Japanese to attack Hawaii. The move of the fleet also threatened Japanese expansion in the Pacific.
1940 (July)
The United States placed an aircraft fuel ban on Japan. This reduced Japan’s import of oil by 90% and left them unable to make further expansive gains.
1940 (August)
Hundred Regiments Campaign
Nearly half a million Chinese troops simultaneously attacked the Japanese in 5 provinces. The campaign led to the deaths of 20,000 Japanese. It also seriously disrupted rail lines making transportation difficult for the Japanese.
1940 (27th September)
Tripartite Pact
Japan signed this treaty of mutual assistance with Germany and Italy forming the Axis Powers. This move by Japan sent a clear signal to the united States that if they used military force on Japan they would also be drawn into war with Germany and Italy.
1940 (September)
This was the name given to a diplomatic code used by the Japanese which was broken by the United States army.
1941 (21st January)
Roosevelt wrote to the US ambassador in Japan stating that he believed the war in Europe and the Japanese threat in the Pacific was part of a ‘single world conflict’. He added that the British Empire supported the British war effort both economically and through military activities. Any territorial changes in Indochina could therefore threaten the war in Europe.
1941 (January)
Admiral Yamamoto began planning an attack on the U.S. fleet at Pearl Harbor.
1941 (27th January)
The US ambassador to Japan informed Washington that he had discovered that Japan was planning an attack on Pearl Harbor. Military experts did not believe Japan capable of making such an attack and felt the attack would be on Manila, capital of the Philippines.
1941 (February)
Admiral Kimmel took command of the fleet based in Hawaii.
1941 (13th April)
Japanese-Soviet Non-aggression Pact
This treaty was signed in Moscow and agreed neutrality between the two countries.
1941 (May)
Japanese admiral Nomura, told officials that he believed the Americans had broken their coded and were reading Japanese messages. The government did not believe the code could be broken and carried on using it.
1941 (15th July)
Japan sent troops into southern Indochina. Britain and the Netherlands had land in the region and many western governments including the United States, froze Japanese assets and refused to export oil to Japan.
1941 (24th September)
Japanese intelligence sent a message to the Japanese consul in Honolulu asking for a grid of locations of ships in Pearl Harbor be deciphered. Admiral Kimmel was not made aware of this request.
1941 (26th July)
The United States froze Japanese assets in America in retaliation for the Japanese invasion of China.
1941 (December)
The Japanese had built 10 aircraft carriers and Yamamoto realised the potential for transporting large numbers of planes and using them as a launch pad. This increased the number of targets that could be attacked since planes did not have to be launched from the home country.
1941 (16th November)
Japanese submarines left Japan bound for Hawaii.
1941 (26th November)
Representatives of the United States met with reprentatives of the Japanese government. However they struggled to find any common ground. The United States were firm that Japan should withdraw from Indochina and halt any further expansion, a requirement that Japan had no intention of meeting.
1941 (26th November)
There was no hope of a diplomatic resolution between Japan and the United States. Admiral Yamamoto ordered the Japanese fleet, including six aircraft carriers, to proceed to Pearl Harbor.
1941 (27th November)
Admiral Kimmel received a message from Washington stating that a Japanese attack in the Pacific was imminent. Despite the warning he did not send planes to see if there were any Japanese aircraft carriers in the vicinity.
1941 (1st December)
President Roosevelt was aware that the Japanese appeared to be preparing for a military offensive in the Pacific. He ordered his top diplomats to find out exactly what the Japanese were up to.
1941 (6th December)
Roosevelt made an appeal to Japan to seek a peaceful resolution to the conflict between the two countries. He did not receive a reply.
1941 (6th December)
U.S. Intelligence decoded a Japanese message which showed that an attack by Japan in the Pacific was scheduled for the morning of the 7th December.
1941 (7th December – 3.42 a.m.)
The Minesweeper USS Condor spotted what they believed to be a Japanese submarine periscope and sent the information and location to the USS Ward.
1941 (7th December – 9 a.m. [5 a.m. in Hawaii])
The information that an attack by Japan was scheduled for the morning of the 7th December reached Washington. Officials suspected the attack might be Pear Harbor. A telegraph message was immediately sent to Admiral Kimmel at Hawaii but it was delayed and he did not receive the message until noon.
1941 (7th December – 6.00 a.m.)
183 Japanese aircraft, including torpedo planes, fighter planes and bombers, took off from aircraft carriers stationed 230 miles north of Oahu.
1941 (7th December – 6.45 a.m.)
The USS Ward found and sank the Japanese submarine.
1941 (7th December -7.00 a.m.)
Despite being aware that the Japanese would attack somewhere in the Pacific, Pearl Harbor had not been placed on alert. Consequently, there were no defensive measures in place and because it was a Sunday people were enjoying a leisurely start to the day.
1941 (7th December -7.02 a.m.)
Army officers at Oahu radar station noticed the incoming planes and reported them to a junior officer. The officer disregarded the report believing the planes to be a force of American B-17 planes that were due to arrive.
1941 (7th December -7.15 a.m.)
A second wave of 167 Japanese aircraft took off from the aircraft carriers stationed 230 miles north of Oahu.
1941 (7th December – 7.15 a.m.)
Admiral Kimmel was told about the Japanese submarine that had been found and sunk. He took no action choosing to wait for verification that the submarine was actually Japanese.
1941 (7th December -7.53 a.m.)
The first wave of Japanese aircraft reached Pearl Harbor and began an air strike on the US battleships at Pearl Harbor and the air stations around the area.
1941 (7th December -8.10 a.m.)
The USS Arizona was hit and exploded killing more than 1,100 men.
1941 (7th December -9.05 a.m.)
The second wave of Japanese aircraft reached Pearl Harbor and began attacking ships and shipyard buildings at Pearl Harbor.
1941 (7th December – 1.40 p.m. [9.40 a.m. Hawaii])
President Roosevelt learned of the Japanese attack on Pearl Harbor.
1941 (7th December -10.15 a.m.)
Japanese aircraft left Hawaii. The attack had destroyed 5 battleships and damaged 8 more. 9 other ships were lost as well as 188 aircraft. 2,335 American servicemen and 68 civilians lost their lives while 1,178 were wounded.
1941 (7th December – 6.40 p.m. [2.40 p.m. Hawaii])
Restrictions were placed on all people of Japanese origin living in the United States. Japanese banks and businesses were closed and their assets frozen.
1941 (7th December – 8.30 p.m. [4.30 p.m. Hawaii])
Roosevelt called an emergency cabinet meeting. Roosevelt declared that ‘a state of war had existed since Japan’s attack’.
1941 (8th December)
Roosevelt spoke to Congress requesting a declaration of war against Japan.
1941 (8th December – 1.10 p.m.)
The attack on Pearl Harbor led to the end of American isolationism as the United States declared war on Japan. Roosevelt declared December 7th ‘a date which will live in infamy..’
1941 (8th December)
Britain declared war on Japan.
1941 (16th December)
Admiral Kimmel and General Short were relieved of their duties.
1941 (16th December)
Admiral Nimitz was given command of the Pacific fleet.


Published Sept 10, 2020 @ 3:40 pm – Updated – [last-modified]

Harvard Reference for this page:

Heather Y Wheeler. (2020). Pearl Harbor, Causes and Main Events 1919 – 1941. Last accessed [date]


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