Pearl Harbor advance-knowledge conspiracy theory facts for kids

Various conspiracy theories suggest that some U.S. government officials knew about Japan's attack on Pearl Harbor on December 7, 1941, before it happened. Since the attack, people have wondered why the United States was caught off guard. They also questioned how much American officials knew about Japan's plans.

In 1944, John T. Flynn, who helped start the America First Committee, wrote a booklet. He claimed that President Franklin D. Roosevelt and his team had been trying to make Japan attack the U.S. This, he argued, would give the U.S. a reason to join World War II. Other writers, like Robert Stinnett and Harry Elmer Barnes, also suggested that U.S. and British officials knew about the attack. They even thought some might have let it happen to get America into the war. However, most historians do not believe this idea. They see it as a fringe theory, meaning it's not widely accepted.

Investigations into Pearl Harbor

The U.S. government held many official investigations into the attack. There were nine inquiries between 1941 and 1946, and a tenth in 1995. These investigations looked into why the U.S. was unprepared.

They found several problems:

• Officials did not fully understand Japan's abilities or plans.
• Too much secrecy about cryptography (code-breaking) caused issues.
• The Army and Navy did not work well together.
• There were not enough people for intelligence work.

Early investigators could not see the most secret information. This was because a general named Henry D. Russell guarded the pre-war decoded messages. He was the only one with access. Later, an investigator named Henry Clausen claimed he was lied to. He said he had to show copies of top-secret decoded messages to prove he had the right clearance.

A full report based on Clausen's work was not made public until the 1980s. It was published in 1992. Some people found it helpful. But one historian noted that Clausen did not talk to General Walter Short, the Army commander at Pearl Harbor. This historian called Clausen's investigation "unreliable" in some ways.

Diplomatic Tensions Before the Attack

Some authors believe President Roosevelt was actively trying to provoke Japan. They say he expected and wanted war. But he wanted Japan to make the first move.

What High-Ranking Officials Said

Rear Admiral Frank Edmund Beatty Jr. was close to President Roosevelt. He said that before December 7, it was clear the U.S. was "pushing Japan into a corner." He believed Roosevelt and Prime Minister Winston Churchill wanted the U.S. to join the war. They felt the Allies could not win without America. Beatty said the demands made on Japan, like leaving China, were so tough that Japan had to react.

Jonathan Daniels, Roosevelt's assistant, also shared a view. He said Roosevelt's reaction to the attack was telling. "The blow was heavier than he had hoped," Daniels noted. "But the risks paid off; even the loss was worth the price."

Ten days before the attack, Henry L. Stimson, the United States Secretary of War, wrote in his diary. He mentioned discussing with Roosevelt how to make Japan "fire the first shot." This was to be done "without allowing too much danger to ourselves." However, Stimson later said that commanders at Pearl Harbor had been warned. He was surprised by their poor readiness. He found it hard to believe that planes were clustered together. Also, anti-aircraft ammunition was not ready.

Robert Stinnett's book Day of Deceit suggests a memo from Commander McCollum was key. Stinnett claims this memo suggested only a direct attack on the U.S. would convince Americans to join the war. This was to help Britain. But there is no proof Roosevelt ever saw this memo. Many in Roosevelt's team insisted on not provoking Japan. Historian Mark Parillo said it would be foolish for Roosevelt to sacrifice a major part of the U.S. fleet just to enter the war.

On November 5, 1941, Navy and Army chiefs warned against war with Japan. They said if Japan was defeated but Germany remained strong, the war would not be won. They wanted to avoid war with Japan to keep helping Britain. Churchill also hoped U.S. aid would "quiet" Japan.

Oliver Lyttelton, a British official, said Japan was "provoked into attacking the Americans." He felt it was wrong to say America was forced into the war. He noted that America was already helping the Allies. For example, the Lend-Lease program supplied war materials to Allied nations. Also, U.S. ships were ordered to report German submarines. Later, they were allowed to "shoot on sight." These actions showed the U.S. was not truly neutral.

Some claims suggest U.S. Naval Intelligence knew about Japanese carrier movements. A Dutch admiral's diary entries from December 1941 were cited. He wrote that he was told two Japanese carriers were west of Honolulu. However, the diary actually used an abbreviation meaning "westerly," not "northwest." Other people at the briefings did not report this.

CBS reporter Edward R. Murrow was at the White House on December 7. He saw officials like Stimson and Secretary Cordell Hull. Murrow wrote that if they were not surprised by the news from Pearl Harbor, they were amazing actors. He believed they were truly shocked. However, one historian noted that Roosevelt seemed less surprised than others. Roosevelt told Murrow, "Maybe you think [the attack] didn't surprise us!"

The McCollum Memo

The McCollum memo

On October 7, 1940, Lieutenant Commander Arthur H. McCollum wrote a memo. He worked for Naval Intelligence. The memo listed eight actions that might make Japan attack the United States. This memo was kept secret until 1994. It famously said, "If by these means Japan could be led to commit an overt act of war, so much the better."

Some, like Gore Vidal, saw this memo as a "smoking gun." They believed it showed a high-level plan to trick Japan into attacking. However, there is little direct proof that President Roosevelt or other top officials ever saw this memo.

Roosevelt and War with Germany

People who challenge the traditional view of Pearl Harbor often say Roosevelt wanted the U.S. to fight Germany. But he did not say this officially. In 1941, the American public did not want war. Historian Thomas Fleming argued Roosevelt wanted Germany or Japan to strike first. But he did not expect the U.S. to be hit so hard at Pearl Harbor.

An attack by Japan on the U.S. would not automatically mean war with Germany. After the attack, American anger was directed at Japan. The Tripartite Pact (Germany, Italy, Japan) said they would help each other if attacked. Japan could not claim the U.S. attacked them if Japan struck first. Germany had been at war with the UK since 1939. It had also been fighting the USSR since June 1941, without Japan's help.

There was already a naval war in the Atlantic between Germany and the U.S. since summer 1941. A German submarine damaged the USS Kearny in October. It killed eleven sailors. Two weeks later, another submarine sank the USS Reuben James, killing 115. Yet, it was only Adolf Hitler's declaration of war on December 11 that brought the U.S. into the European war.

A Japanese message from November 29, 1941, stated that Germany would join immediately if Japan went to war with America. Some see this as proof of a guarantee. Others see it as Germany promising to help Japan if needed.

Japanese Codes and Secrets

In 1941, U.S. signals intelligence was advanced but also had weaknesses. In 1929, a U.S. code-breaking group was shut down. This led to other countries changing their codes.

However, U.S. code-breaking continued in secret. The Army and Navy had their own groups. Code-breaking was so secret that major commands, like Pearl Harbor, were not allowed to do it.

By late 1941, the U.S. had broken some Japanese codes. The highest diplomatic code, called "Purple" by the U.S., had been broken. But American code-breakers had made little progress on the Japanese Navy's main code, called JN-25.

There was also a shortage of trained people. Translators were overworked. Code-breakers were few. Staffs were stressed. Not every Japanese message was decoded. The U.S. also received decoded messages from Dutch intelligence. But the U.S. did not always share its own findings. This was partly due to fears of secrets getting out. Even President Roosevelt did not always get all the information.

Purple Code

The "Purple" code was used by the Japanese Foreign Office for diplomatic messages. It was broken by U.S. Army code-breakers in 1940. A 14-part message in this code was sent from Japan to its embassy in Washington. It was decoded on December 6 and 7. This message clearly showed Japan's plan to end diplomatic talks with the U.S. It was to be delivered at 1 p.m. Washington time (dawn in the Pacific).

The U.S. decoded the first 13 parts. But the 14th part was decoded too late. Colonel Rufus S. Bratton, an intelligence chief, thought the message only meant a break in talks. Others saw it differently. Roosevelt, after seeing the first 13 parts, said "this means war." When General George Marshall got the message on December 7, he ordered a warning sent to U.S. bases, including Hawaii. But due to bad radio conditions, the message was sent by undersea cable. It did not arrive until the attack was already happening.

Some claim no Japanese Navy message before the attack mentioned Pearl Harbor. This might be true. The Japanese Foreign Office was often kept out of military planning. It is also possible that some messages were not translated until after the attack, or even after the war. Not all pre-attack messages have been made public. So, it's unclear what they might have contained.

JN-25 Code

The JN-25 code was the Imperial Japanese Navy's main code. It was a very complex system. Breaking such a code was extremely difficult. It took a lot of effort and time. Code-breakers needed many intercepted messages to even begin. Before December 7, 1941, Japanese Navy radio traffic was limited. This made it harder to gather enough messages to break the code.

Breaking this code was a three-step process. First, finding the starting point. Second, removing the main layer of encryption. Third, breaking the actual code. Only after the third step could the message be read. Even then, its meaning might not be fully clear. When Japan released a new version of the code, code-breakers had to start all over again.

Many claims have been made about how much of JN-25 was readable before the attack. Some say U.S. code-breakers could "walk right across" the messages. But this likely referred to an easier way to attack part of the code, not fully read the messages. Reports show that only about 7% of the code groups had been recovered by the time of the attack. No JN-25 messages fully decoded before Pearl Harbor have ever been found or made public. Experts say it was not possible to produce usable decoded messages at that time.

U.S. Navy planners were so sure Japan could only do one big operation at a time. So, when they saw Japan preparing for operations in the Dutch East Indies, they stopped looking at other JN-25 messages for two weeks.

Japanese Spies and Information

Japan had spies working against Pearl Harbor. One was Takeo Yoshikawa, a Japanese Navy intelligence officer working undercover at the consulate in Hawaii. He was young and sometimes made mistakes. But Pearl Harbor's security was so loose that Yoshikawa could easily get information. He even took the Navy's own harbor tour boat. Hills overlooking the harbor were also open for observation.

Some of his information was sent to Japanese intelligence officers on commercial ships visiting Hawaii. Most of it was sent to Tokyo by cable. The U.S. intercepted and decoded many of these messages. But most were seen as normal intelligence gathering. They did not suggest an active attack plan on Pearl Harbor.

In November 1941, ads for a board game called "The Deadly Double" appeared. They had headlines like "Achtung, Warning, Alerte!" and showed dice with numbers like 12, 24, XX, 5, 7, and 0. Some later wondered if these were secret messages warning of the Pearl Harbor attack on December 7 (12/7) at latitude 20 (XX). But the game was real and was sold.

Radio Signals and the Japanese Fleet

Some people claim that as the Japanese fleet, called the Kido Butai, sailed toward Hawaii, U.S. ships heard radio signals. These signals supposedly warned U.S. intelligence of the coming attack. For example, the ship SS Lurline was sailing to Hawaii. Its radio operators claimed to hear unusual Japanese radio traffic. They said it came from a source moving east.

However, surviving Japanese officers say their ships kept strict radio silence. Their radio operators were left in Japan to send fake traffic. All transmitters on the ships were disabled to prevent any accidental broadcasts.

The Kido Butai did receive intelligence updates. Even if they did not transmit, their antennas could pick up signals. Some argue that these receiving antennas might have passively "rebroadcast" signals. But this would have been very weak and not useful for tracking.

A radio direction finder (DF) from that time could only tell the compass direction, not the distance. To find a target, two DF stations were needed to triangulate its position. If the target was moving, the detections had to be close in time. This complex process did not happen. If the Kido Butai was detected, it was not tracked.

The original records from the Lurline have disappeared. So, there is no written proof from that time about what was recorded. The ship's radio operator later recreated a logbook. But the directions he gave were far off from the known Japanese fleet positions. They pointed toward Japan.

Japanese Radio Silence

According to a 1942 Japanese report, the fleet kept "strict radio silence." They even removed fuses and sealed keys on transmitters. Commander Minoru Genda, who helped plan the attack, also stated, "We kept absolute radio silence." For two weeks before the attack, the ships used flag and light signals. This was enough because they stayed close together.

A communications officer on one ship even dismantled vital transmitter parts. He kept them in a box he used as a pillow. This was to prevent any transmissions. There is nothing in Japanese logs or reports that shows radio silence was broken before the attack.

Radio Tricks and Deception

The Japanese used radio deception. An intelligence officer stated that false communications were sent from Kyushu. These messages used the same time and wavelength as during training. This made U.S. intelligence, like Commander Joseph Rochefort in Hawaii, believe the Japanese carriers were still in home waters. The ships left their regular radio operators behind to send "routine" traffic. Japanese naval bases also sent out many fake radio messages.

Analysis of radio bearings from U.S. stations showed that the signals came from Japanese naval bases, not from where the fleet actually was. On November 26, U.S. intelligence reported that all Japanese aircraft carriers were at their home bases.

However, Rochefort later said he recognized the Akagi's radio operators. He said they had a "ham-fisted" style. The Japanese say these operators were left behind as part of the deception.

To trick listeners, the IJN Settsu sailed from Taiwan to the Philippines. It pretended to be all six fleet carriers and two light carriers.

U.S. Contact with Japanese Submarines

Japanese submarines were seen and attacked by the U.S. destroyer Ward outside Pearl Harbor. This happened a few hours before the air attack. At least one submarine was sunk. This could have given enough warning to prepare. But the duty officers reacted too slowly.

After the attack, the search for the Japanese fleet focused south of Pearl Harbor. This continued the confusion.

Allied Intelligence Information

In Hawaii, Naval Intelligence had been tapping phones at the Japanese Consulate. They heard a strange talk about flowers in a call to Tokyo. But the phone tap was discovered and removed in early December. The local FBI office was not told about the tap or its removal.

Throughout 1941, the U.S., Britain, and the Netherlands gathered information. It suggested Japan was planning new military actions. The attack on Pearl Harbor was actually a smaller part of Japan's main plan. Their main goal was to attack British Malaya and the Philippines. Many more resources were used for these attacks.

Many in the Japanese military disagreed with Admiral Isoroku Yamamoto's idea to attack the U.S. fleet at Pearl Harbor. This idea was first proposed in early 1941. Even after the Navy approved planning, some remained reluctant.

U.S. intelligence correctly believed Japan would focus on Southeast Asia. There were warnings of attacks on Thailand, Malaya, French Indochina, the Dutch East Indies, and the Philippines. Pearl Harbor was not mentioned. When the final part of the "14-Part Message" was received, an officer tried to link it to a Japanese convoy heading for Thailand.

The U.S. Navy knew about Japan's traditional war plans. These plans expected a big battle between battleships near Japan. This battle would happen after U.S. ships were weakened by night attacks. This strategy expected Japan to wait for a U.S. attack. Yamamoto's decision to attack Pearl Harbor and use aircraft carriers was a big change. This new plan left analysts confused.

There was a specific claim of a Pearl Harbor attack plan from the Peruvian Ambassador to Japan in early 1941. The source was the Ambassador's Japanese cook. This was seen as unreliable and was not taken seriously. Later reports from a Korean labor group were also doubted. In August 1941, British Intelligence sent an agent, Duško Popov, to warn the FBI. He said Germany was asking for details about Pearl Harbor's defenses. This request came from Japan. But the FBI did not act on this information.

British Knowledge Claims

Some authors claim that Winston Churchill knew about the Pearl Harbor attack beforehand. They say he chose not to tell the Americans to get them into the war. These authors suggest Churchill knew Japan was planning an attack by mid-November 1941. They also claim he knew the Japanese fleet left port on November 26. Finally, they say British intelligence intercepted a message on December 2. This message supposedly indicated December 7 as the attack day.

One author claimed a British intelligence committee discussed the attack on December 5, 1941. He said they knew a Japanese fleet was sailing toward Hawaii and confirmed the Americans were informed. However, this author was wrong. There was no meeting on December 5, and Pearl Harbor was not discussed when they met on December 3.

U.S. War Warnings

In late November 1941, both the U.S. Navy and Army sent clear warnings of war with Japan. These warnings went to all Pacific commands. On November 27, Washington sent a final alert to commanders like Admiral Husband E. Kimmel at Pearl Harbor. It said, "This dispatch is to be considered a war warning...an aggression move by Japan is expected within the next days."

These messages clearly stated that war with Japan was very likely. They told commanders to be ready. But they did not specifically mention an attack on Pearl Harbor. Instead, they focused on the Far East. Washington did not send the raw intelligence it had to commanders in Hawaii. It also sent little of its own analysis. Washington did not ask for their opinions. Some criticized these warnings for being "conflicting and imprecise."

The Army was in charge of defending Pearl Harbor and Hawaii. General Short, the Army commander, told Washington he had increased his alert level. But Washington did not understand what he meant. Short was mainly worried about sabotage from spies. This is why he ordered Army Air Corps planes to be parked close together. He did not seem to increase urgency about using radar equipment. Anti-aircraft guns were not ready. Long-range bombers were not used effectively. Short did not seem to understand his job was to defend the fleet.

In Short's defense, he had training duties. Also, the best patrol planes were needed in the Philippines and Britain, which had higher priority.

Little was done to prepare for an air attack. Rivalries between Admiral Kimmel and General Short made things worse. Most intelligence went to Kimmel, assuming he would tell Short, and vice versa. This often did not happen. Hawaii did not have a Purple code machine. So, it depended on Washington for intelligence from that source. But Short had no contact with Kimmel's intelligence staff. So, he was often left out.

Henry Clausen said the war warnings could not be more precise. This was to avoid Japan knowing the U.S. was reading their secret messages. He also said Kimmel and Short should have understood the warnings better. They should have been more watchful. All other Pacific commands took proper steps for their situations.

Clausen, like most, ignores what the "war warnings" actually warned against. Washington expected an attack somewhere else, not Pearl Harbor. Since Japan was already sending troops to Thailand, it seemed another major operation was impossible. Kimmel and Short took steps against sabotage, which was expected. They did not expect an air attack. No one explicitly did. The common belief was that Japan could not do two major naval operations at once. So, with the Thailand invasion known, Hawaii commanders felt safe.

The Philippines also had full access to decoded messages. Yet, General MacArthur was also caught unprepared. His planes were on the ground nine hours after the Pearl Harbor attack.

Some argue there was enough intelligence to give Pearl Harbor commanders a higher alert. But information can seem clearer after the fact. At the time, it was mixed with thousands of other intelligence bits. Some of these bits pointed to other possible Japanese attacks.

The Role of U.S. Aircraft Carriers

None of the three U.S. Pacific Fleet aircraft carriers were at Pearl Harbor during the attack. Some claim this proves officials knew about the attack. They say the carriers were moved to save them.

However, the two carriers with the Pacific Fleet, Enterprise and Lexington, were on missions. They were delivering fighter planes to Wake and Midway Islands. This was to protect the route for planes going to the Philippines. The third carrier, Saratoga, was being repaired. At the time of the attack, Enterprise was about 200 nautical miles west of Pearl Harbor. It was heading back. It was supposed to be back on December 6 but was delayed by weather.

At that time, aircraft carriers were seen as scouting ships. They were not considered as important as battleships. Battleships were the most important vessels in naval planning. This was based on the Mahan doctrine, followed by both the U.S. and Japanese navies. Carriers became the Navy's most important ships only after the attack.

If the U.S. wanted to protect its key assets, it would have focused on battleships. The Pearl Harbor attack showed how powerful carriers could be. They could attack enemies far away with great force and surprise. The U.S. would later use this power against Japan. The loss of battleships at Pearl Harbor forced the U.S. to rely on carriers for offensive operations.

No Court-Martial for Commanders

Another point in the debate is that Admiral Kimmel and General Short were never court-martialed. Some claim this was to avoid revealing that the U.S. had advance knowledge of the attack. Kimmel himself said he believed most "incriminating records" had been destroyed. He doubted "the truth will ever emerge." Vice Admiral Libby said he believed Roosevelt ordered Pearl Harbor to happen. However, it is also likely that a court-martial was avoided to keep the secret that Japanese codes were being read, especially during wartime.

Secret Information Not Released

Part of the debate is about documents related to the attack. Some Pearl Harbor documents have not been made public. Some may no longer exist. Many were destroyed early in the war due to fears of a Japanese invasion of Hawaii. Others are incomplete.

Information that is still secret includes key reports in Churchill's records. For example, a file dealing with the Japanese situation in 1941 is mostly open. But Section 5, covering November 1941 to March 1942, is "closed for 75 years." Unlike U.S. intelligence files, the British government has not released its secret files about Japan.

There are also conflicting stories about requests for documents. Many documents were said to be automatically destroyed during the war. But authors have continued to get classified Pearl Harbor materials released through the Freedom of Information Act.

For example, a document called Sheet No. 94644 is mentioned in released Japanese Navy Movement Reports. It notes "FAF using Akagi xtmr" (First Air Fleet using Akagi's transmitter). This suggests a reported position. But these documents have not been fully declassified.

Fake Documents

A supposed transcript of a conversation between Roosevelt and Churchill in late November 1941 was found to be fake. Many claims about these conversations are based on fictional documents.

Images for kids

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  U.S. propaganda poster calling for revenge for the Pearl Harbor attack.