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Throwback Thursday

Benjamin Felix

Ben Felix
November 19, 2007
American History

Pearl Harbor and the Magic leak

The attack on Pearl Harbor was a disaster.  The leak in a code-breaking intelligence program called Magic may have influenced the ultimate consequences of the Japanese bombardment.  In scholarly articles Ruth R. Harris and James Montgomery discuss different interpretations of the Magic leak as an important factor in the attack.  They engage in a direct discussion as Montgomery replies to Harris’ writing.  The criticism is quite harsh in the writings while the two historians pick each other’s work apart.  Each argument has valid points of strength and weakness, and all of these things are discussed in the writings.  This scholarly exchange provides some very different perspectives on aspects of the Magic leak’s effect on the outcomes of Pearl Harbor

The Japanese planned their attack on Pearl Harbor because they saw its location as a direct threat to the security of their country; they knew that if America became involved in the war they would have a perfect base to attack Japan from.  Japan’s decision makers knew that they needed to eliminate this threat before America became involved.  The attack was planned to give the Japanese a chance against a much more powerful enemy.  They learned eight months before the attack that the Americans had broken their code. This intelligence leak seems to have arisen when the British embassy sent an account of one of their diplomat’s secret conversations with Sumner Welles about Japanese and German discussions to London.  The message was not sent in the standard coded format that would have normally been used for something of this level of secrecy, but in a code designated for less confidential information.  The British did not want to place strain on their encryption equipment and personnel.  This raised great controversy within the Allied diplomatic circles as these messages were intercepted by the Germans.  From the interception they were able to deduce that the Americans must have the ability to decode Japanese messages; there was no other way that they could have learned about these high security and top secret exchanges so quickly.  When the Germans learned about the American breakthrough they promptly passed the intelligence onto the Japanese with whom they had signed a treaty.  The Japanese may not have believed what the Germans told them and the way that they reacted to the information can be interpreted in two different ways: They may have used the information as an advantage, or they may have not heeded the German warning and continued passing information through the breached communication lines.  Either way the Japanese chose to handle that situation, their Admiral, Yamamoto, recognized that destroying the Pacific Fleet at Pearl Harbor was the only hope for defeating the Americans.  It was obvious that the Americans were a militant superpower, and their base at Pearl Harbor would be a sure fire attack on Japan if they went to war.  The American’s success in breaking the Japanese Purple Code allowed them to intercept Japanese messages and learn about the possible threats.  Although the White House did not seem overly concerned with the information it was gaining through this program, Pearl Harbor was put on full Alert just in case an attack was in actuality imminent.  The American General Short ordered the majority of the air to air combat aircraft to be concentrated in the middle of their airfields because he was worried that Japanese American citizens might attempt to cripple the American planes before the mainland began their attack.  The Japanese Americans had in fact been in America for several generations and had no intentions of aiding Japan; their unfair treatment by the government was later compensated for with money when it was realized how big of a mistake this was.  These American citizens were essentially placed in concentration camps during the time of tension with Japan.[1]

The Japanese sent a series of fourteen radio messages to the United States that ultimately stated their intent to declare war.  The messages were passed to the Defense Department but it was not taken as a big deal when they were received.  The reality of a threat continued to materialize but the highest commanders were hesitant to take serious action.  Although the Pearl Harbor base was put on full alert, aggressive defensive action was not taken to counter the possible Japanese attack.  That same day an American destroyer observed and sank a Japanese submarine that was trying to break through the security net that surrounded the harbor and the ship notified the base.   This warning was disregarded by the Captain on duty at the base because he thought that the new commander of the destroyer had just gotten overly excited about a menial event.  The Japanese war planes were actually seen on the base’s radars as they approached their target, but it was thought that they were a fleet of bombers coming home and a Lieutenant in charge of radar told the trainee technicians not to worry about it.  The Japanese planned for their declaration of war to be received by the Americans at 1 pm, thirty minutes prior to the attack, but the messages were translated too slowly.  When the attack planes arrived they were met with no initial resistance from the stunned Americans.  The declaration that the Japanese had tried to send was finally translated well into the attack.  The attack on Pearl Harbor was catastrophic for the Americans, but not completely.  Because they were somewhat concerned of Japanese hostility American officials had sent two of their aircraft carriers, the USS Enterprise and the USS Lexington out to sea to look for the Japanese fleet.  These two ships were detrimental for any American retaliation and had they been destroyed this attack would have had a much greater effect.[2]

The element of surprise was the key to the Japanese success at Pearl Harbor.  Although they did want to warn the Americans of what was coming as a kind of courtesy, they made sure to give very short notice to confirm their success.  Their transmissions declaring war were not received as promptly as they had hoped; this mistake struck fear into the Japanese because they did not want to anger America.  The Magic program instituted American cryptanalysists that worked tirelessly to decode the Japanese’ diplomatic messages and gain intelligence.  This program sprung a leak that gave Japan the knowledge that their messages were being decoded.  Having this information that the Americans knew what they were communicating between themselves and their allies may have given them the opportunity to relay false information and further their ability to attack the Americans by surprise.  It is also possible that the Japanese’ knowledge of Magic may have been completely inconsequential.  If the Japanese were able to use their knowledge of the Magic program, it gave them a great advantage.  It can be argued, however, that they did not in fact know about the leak.  They may not have believed the Germans when they relayed their discovery of what the Americans were in possession of.  In short articles Ruth R. Harris and James Montgomery pursue a historical discussion through correspondence in their writings that addresses these possibilities.[3]

Ruth R. Harris discusses this issue in her article, “The Magic Leak of 1941 and Japanese American Relations.”  Japan learned that the Americans had been decoding their messages eight months before they became hostile towards the United States.  The Japanese did not change their code system after they knew that the Americans could decipher their messages; they enacted futile security measures which gave the Americans plenty of Japanese diplomatic interactions to read.  She bases her discussion on documents that had been released recently when she wrote the article.  She claims that the evidence in these documents will provide new information that shows the leak of secret information allowed the Japanese to gain an advantage in grooming their surprise attack.  She claims that the Japanese did not change their diplomatic code, and the security measures that they took were not going to have any real effect on the Americans ability to decode their ciphers.  It is speculated through her writing in this article that they did not change their code because they saw an opportunity.  They wanted the Americans to think that they were gaining valuable information through their efforts while really giving the Japanese a means of providing false information to American intelligence networks.  Harris recounts a Japanese message that was actually intercepted by the Americans in which it was stated to an Ambassador that no confidential information could be passed through intelligence lines because they feared that the lines were compromised.  This message shows that the Japanese were definitely aware of the American intelligence breakthrough, but were still sending information through these lines.  American signal intelligence determined that the Japanese did in fact stop sending the most secret messages in the code that they had broken; they discovered a new code that the Japanese had adopted.  It was a code “considered to be of the highest type of secret classification,”[4] the new code was now used for important transmissions while the breached code also continued to flow.  This shows that although they were still sending messages in the jeopardized code, their top secret information was sent through a new more secure code.  From this it can be inferred that the secondary messages sent through the old system were not containing information of any real importance to Japanese security.  This evidence supports the hypothesis that the Japanese used the code that they knew to be broken in order to supply Americans with manipulative information.[5]

Harris thoughts rely on the assumption that the Japanese believed what the Germans had told them.  It is claimed by James Montgomery in his article “Communications” that there is evidence to support other ideas.  Some Japanese may have believed that it was in fact the Germans that had been reading their messages; in this case they would have thought that the Germans saying this was an attempt to divert attention away from what they were trying to do.  This theory makes the Japanese appear skeptical of their sources.  This would mean that the Japanese’ failure to change their codes was a mistake caused by Japanese doubts of the Germans as an honest source, not a Japanese attempt to sabotage American Intelligence.  It was also seen as a possibility that it was not the Americans that were the problem at all, but a spy within the Japanese diplomats that was selling information.  This fear would have given reason to conduct a search within the Japanese circles during which their codes would need to stay the same so as not to tip off the mole.  The last doubt of the Japanese stemmed from the possibility that the Americans were in fact intercepting their messages, but only some of them.  They would have assumed that the intercepted messages were not of great importance and that they could continue to send their secret messages.  The Japanese’ lack of knowledge of the American sophistication in communications technology, which was exposed after the war, would support this theory.  It is stated in Montgomery’s article that the Japanese did not change their codes, nor did they stop sending important policy decisions; the Whitehouse was not deliberately misled following the magic leak.  Shigenori Togo, the new foreign minister in place after the fall of the Kanoye cabinet, was quoted saying that he had been assured that any Japanese dispatches being sent were entirely secure.  It is also noted by Montgomery that the Japanese messages that continued to be sent hint towards Japanese attack, if they are interpreted properly.  The assertion that Ruth Harris makes in her article that Japanese transmissions were restricted after August 7, 1941 is rejected by Montgomery on the basis that Magic documents after this date gave plenty of warnings that Japan would soon become hostile.  These arguments point to Americans being inept at elucidating the information behind the messages.  Although they may have been able to decode the messages, the words they were decoding then had to be translated.  The type of code machines that were generally used during this time period incorporated many shortened versions of words used to increase the overall security of the message.  These bumps in the decoding process could have caused the information to be decrypted in a way that did not expose hints of an attack. After the events actually occurred, however, the messages could be looked back on and the proper interpretations would be much easier to see.[6]

Harris disagrees.  She speculates that incorrect interpretation is not what caused the Americans to be unprepared for attack.  She states that through the Magic program the presidential advisors were able to devise that if the American-Japanese relations continued to sour that Japan would attack several possible locations, all completely unrelated to Pearl Harbor.  She speculates that the administration let its guard down due to the intelligence they had through their efforts in decrypting the Purple code; the government found out not long after the attack that the information they had been receiving from the Magic program had been wrong.  Because of the misinformation that they had been using to defend the country, the U.S. administration was surprised when their important naval base was attacked.  Everything had been kept completely secret from the Japanese end.  Due to the level of secrecy and intelligence countermeasures that the Japanese used, the Americans were not digging for anything like an attack on one of their military strong points because they thought they had already secured the means to intercept any news of an attack.  This shows that the leak in the Magic program proved to have dire consequences for the Americans.  If the Magic documents had never been presented to American officials they might have been more concerned with looking into Japanese foreign policy during this time of political tension.  Their confidence in this information created a feeling of wisdom in how the Japanese would begin hostile action against their enemies.  The Japanese, whether they knew it or not, were able to use the magic leak to assist them in a surprise attack, claims Harris.[7]

James Montgomery takes a different stand on this issue.  He claims that the documents that the Magic program produced did in fact have sufficient information to predict the attack and had the Americans interpreted it in a different way they would have realized the imminent threat.  The proper path leading to the correct interpretation is much easier to see after the events actually happened than when trying to predict what is going to happen.  This may have caused the good information that American Intelligence had in their hands to slip through their fingers.  Montgomery claims that although failures in American Intelligence did lead to Pearl Harbor being a disaster, the Magic leak was not one of these.  He stands by his feelings that the Japanese did not believe the warnings that they received from the Germans and that the Magic leak was inconsequential, having no effect on how the attack happened.[8]

Ruth R. Harris and James Montgomery take two very different standpoints on the value of the information that the Japanese may have gained through the leak in the Magic program.  Harris believes that the Magic leak had great consequences in the final outcomes of the attack on Pearl Harbor and Montgomery believes that the leak was an arbitrary event in determining the final result.  Ruth Harris’ arguments are based around some “new information” that had recently been de-classified when she wrote her article.  The main point she makes is that the Japanese knew that the Americans had their codes and they used this to sabotage the American intelligence program.  She asserts that this Japanese action caused great harm to the Americans’ ability to discover their plans to attack.  Montgomery disagrees with what Harris writes.  He directly mentions and denounces her article throughout his writing.  His opinion is that the leak did not have any effect on what happened at Pearl Harbor.  He feels that even had the leak not happened the outcomes would have been the same.  He writes that the Japanese did not stop sending secret messages in their code; the Americans were just unable to see the hints within the Japanese code that they were decoding that could have helped them predict the attack.  The two writers have very different opinions backed by valid arguments.

[1]{C} Sullivan, Robert, “Pearl Harbor – What Really Happened.” Time (2001): full article [journal online]; available from http://www.time.com/time/columnist/klein/article/0,9565,128065-3,00.html; internet; Accessed November 3 2007.

[2]{C} Sullivan, Robert, “Pearl Harbor – What Really Happened.” Time (2001): full article [journal online]; available from http://www.time.com/time/columnist/klein/article/0,9565,128065-3,00.html; internet; Accessed November 3 2007.

[3]{C} Sullivan, Robert, “Pearl Harbor – What Really Happened.” Time (2001): full article [journal online]; available from http://www.time.com/time/columnist/klein/article/0,9565,128065-3,00.html; internet; Accessed November 3 2007.

[4]{C} Ruth R. Harris, “The Magic leak of 1941 and Japanese-American Relations,” Pacific Historical Review 50.1 (1981): 77-96

[5]{C} Ruth R. Harris, “The Magic leak of 1941 and Japanese-American Relations,” Pacific Historical Review 50.1 (1981): 77-96

[6]{C} Ruth R. Harris, “The Magic leak of 1941 and Japanese-American Relations,” Pacific Historical Review 50.1 (1981): 77-96; James Montgomery, “Communications,” Pacific Historical Review 51.2 (1982): 239-242

[7]{C} Ruth R. Harris, “The Magic leak of 1941 and Japanese-American Relations,” Pacific Historical Review 50.1 (1981): 77-96; James Montgomery, “Communications,” Pacific Historical Review 51.2 (1982): 239-242

[8]{C} James Montgomery, “Communications,” Pacific Historical Review 51.2 (1982): 239-242