On Sunday, 7 December 1941, at 7:55 A.M. the Japanese Imperial Navy launched a surprise attack on the United States Pacific Fleet located in Pearl Harbor, Hawaii. The theories and explanations of the events surrounding the Japanese attack on U.S. forces have become a cottage industry for historians of World War II.
Questions about U.S. military involvement, and theories of how it happened and who knew what and when, reappear with each tenth anniversary. As early as 1942 opponents of President Roosevelt accused him of working to bring the United States into World War II and using the Japanese attack on the United States as an excuse to do just that.
The events surrounding the attack have been subject to multiple interpretations. John Toland, Robert B. Stinnett, James Rusbridger, and Eric Nave have been among those who argued that a conspiracy existed to use an attack on Pearl Harbor to bring the United States into the war and was the real reason for the Japanese success.
Others led by Gordon Prange, Roberta Wohlstetter, and Henry Clausen have argued that it was a series of errors on the part of the United States that gave Japan its opportunity. Since the end of the war, large amounts of information about who knew what have emerged, often providing more smoke than light.
The attack caught a large number of U.S. warships in the harbor. The Japanese sank or damaged eight battleships, two beyond repair. They also damaged three light cruisers, three destroyers, and four other ships beyond repair.
In the U.S. Navy and Marines, 2,086 were killed and 749 wounded, and in the army 194 were killed and 360 wounded. In addition, the United States lost 188 aircraft. Japanese losses were fewer than 100 personnel and 29 aircraft. The event shocked the United States, which had been used to the idea of security within the territories.
The United States and Japan had become significant competitors in Asia prior to the war. U.S. policy in the Pacific during the 1930s and early 1940s was perceived by the Japanese as hostile to their interests in the region. At the same time, Japanese expansion in the region was seen in Washington as hostile to U.S. interests in Asia.
U.S.–Japanese relations were deteriorating throughout 1940–1941 and as the situation became more likely to move to a military solution, U.S. planners foresaw a potential Japanese attack on U.S. interests in the Pacific, especially in the Philippines where the United States had a significant military presence, led by General Douglas MacArthur. The movement of the U.S. Pacific Fleet from San Diego to Hawaii in 1940 was done with a purpose as well. Its placement there was a statement of U.S. interest and intent in the region.
Hawaii was a less secure location than California. There had already been a number of studies showing the possibility of an air attack against Pearl Harbor. The possibility was considered significant enough that on 7 February 1941, General George Marshall (U.S. Army chief of staff) sent Lieutenant General Walter Short (commanding general of the Hawaiian Department) a message informing him that “the risk of sabotage and the risk involved in a surprise raid by air and by submarine constitute the real perils of the situation”.
Then on 5 March 1941 another message from Marshall informed General Short: “I would appreciate your early review of the situation in Hawaiian Department with regard to defense from air attack. The establishment of a satisfactory system of coordinating all means available to this is a matter of first priority”. On 27 November 1941 the commanders in the Pacific were sent what has become known as the “war warning” message.
Marshall’s message cautioned of potential Japanese action “at any moment” and also informed General Short, “Prior to hostile Japanese action, you are directed to undertake such reconnaissance and other measures as you deem necessary”. In the navy message it noted the movement of an “amphibious expedition against either the Philippines, or the Kra Peninsula or possibly Borneo”.
The use of intelligence has been a significant problem in clearing up the questions around the attack. The United States had broken a number of Japanese codes including the “Purple Code” (the highest Japanese diplomatic code) and realized that relations with Japan were deteriorating toward war.
The most famous message intercepted in the last twenty-four hours before the attack was the “Fourteen Part Message,” which was itself of little intelligence value except that it showed the state of U.S.–Japanese relations.
More important was the order setting the time of delivery of the Fourteen Part Message as 1 P.M. in Washington, 7:30 A.M. in Hawaii. General Marshall ordered that the information be communicated to the Pacific commanders by the fastest possible method.
There is a discrepancy in the number of times Marshall was alleged to have sent officers to check on the delivery time, but he is known to have done so at least once. Due to atmospheric conditions the message was sent to Pearl Harbor by telegraph and did not arrive until after the attack on the base.
There were other significant messages, including one from Hawaii to Japan laying out the positions of U.S. ships in the harbor. In December before the attack, the United States had access to information that the Japanese diplomats had been ordered to prepare to destroy their codes.
On 6 December 1941 Colonel Bicknell, the assistant chief of staff, announced to General Short’s staff that “he had received information to the effect that the Japanese counsels were burning their papers .... It would at least show that something was about to happen, somewhere”.
In spite of these successes, it needs to be remembered that the number of codes broken by the United States was limited, as was the completeness of the information about Japanese intentions. Thus, preparations for war were conducted with only partial knowledge.
Another source of concern is the location of aircraft carriers. The U.S. Navy’s Pacific aircraft carriers were not present on the day of the attack. The Saratoga was in San Diego, while the other two U.S. carriers were off to reenforce forward bases with aircraft.
The USS Enterprise had gone to Wake Island and was scheduled back to Pearl Harbor around 7 A.M. on 7 December, but was held up by bad weather, and the USS Lexington was on its way to Midway Island.
The Enterprise was close enough at the time of the attack that its aircraft were able to make contact with Japanese aircraft. Their missions saved them for use in the important sea battles to come, Coral Sea and Midway.
One theory argues that President Roosevelt knew about the coming attack, but was willing to sacrifice the aging battleships in order to give cause to the American people to fight the war. In order to do this, Roosevelt and the military command structure in Washington not only placed the U.S. battleships in harm’s way, they also sent U.S. aircraft carriers away from the site of the attack to protect them.
Then Washington conspired to deny U.S. commanders in the Pacific important intelligence data that would have led them to assign a higher state of alert on 7 December. There is significant circumstantial evidence for this theory, based on the idea that Roosevelt needed a military disaster to enter the war. This theory does not account for the possible impact of an attack on other U.S. forces, or a successful defense against a strong attack on Pearl Harbor.
It also does not account for Roosevelt’s love of the navy, which makes his willingness to sink ships less likely. This theory assumes that Roosevelt and the naval leadership understood that aircraft carriers would dominate the next naval war; the evidence for this idea is limited.
It also assumes that the intelligence clearly pointed to an attack on Pearl Harbor. The challenge when investigating the subject is in separating the information that is meaningful and important from a flood of extraneous information.
As one historian notes: “we failed to anticipate Pearl Harbor not for a want of relevant material, but because of a plethora of irrelevant one”. Without a message specifically stating an attack on a site, an analyst must interpret the message and weigh its value based on what they know about an adversary’s potential and preferences.
It is often easier to see a clear meaning in a message with hindsight. Another variant of this conspiracy argues that the British government knew about the attacks and did not inform the United States in order to force it into the war.
It is based on the existence of both British intercept operations, based on U.S. efforts, and British agents in the regions. The strength of this theory is that the British did have the technology to break the “Purple Code,” which they gained from the United States and from the timely sale of British interests in Asia.
This theory assumes superior British knowledge of Japanese intentions, for which the evidence is weak. And like Roosevelt, Churchill loved the navy. It was unlikely he would risk lives, or potentially the war, by allowing the U.S. Pacific Fleet to be destroyed.
The Conspiracy’s Place in History
There were numerous official investigations of the events around Pearl Harbor from the very beginning. The army and navy each conducted board and individual inquiries, such as the Roberts Commission, the Hart Inquiry, the Army Pearl Harbor Board, the Navy Court of Inquiry, the Clarke Inquiry, the Clausen Investigation, and the Hewitt Inquiry.
In 1946 Congress conducted its own investigation and pulled together all of the previous efforts. There has been renewed interest in events around Pearl Harbor since its fiftieth anniversary in 1991. This has spawned a renewal in many conspiracy theories, but also created a growing interest in understanding the actual events and causes of the events of 7 December 1941.