The primary impression of United States involvement in World War II is that war began the early hours of December 7th, 1941 when the Japanese gave surprise aerial attack on Pearl Harbor and its surrounding installations. While there is a level of academic debate on the validity of that assessment, one thing is certain: The full United States entry into World War II was one of anger and determination in response to Pearl Harbor. Though there is still much debate on how much, if any, warning the United States had that attack was imminent by December 1941. Through historical writing, one can view the varying interpretations from the first-hand accounts to academic print spanning over half a century.

            World War II is quite possibly one of the most studied and researched topics in the history of modern society, and while it is often perceived that everything to be said about the war has been said, this could not be further from the truth. These works encompass not only primary source material from participants, but also more modern declassified materials from varying agencies in many of the participant nations. The authors presented through this analysis form varying interpretations of the how, why, and when the United States involvement in World War II truly began. Many automatically think of the Japanese attack on Pearl Harbor as the start of war for the USA, but there are scholars who theorize that the US was quietly involved long before.

            Though officially the United States remained neutral during the early part of Europe’s struggle against the Axis powers, President Roosevelt offered assistance to Britain and other allies that lacked the proper means to fight against Hitler and his allies (such as Japan), and the article presents this information in such as a way that ensures the reader considers this as unofficial participation, thus adding to the point that World War II began, in many ways, before Pearl Harbor.

            Author, historian, and Associate Professor of National Security Affairs at the Naval Postgraduate School Christopher Darnton states his approach that documentary evidence now features on both sides of important debates in which the persuasiveness of contending theories hinges on the assessment of specific historical cases.[1] Darnton’s work features cogent yet starkly divergent historical claims pertaining to the arguments that the US intentionally provoked the governments of the Axis powers in the months preceding the attack on Pearl Harbor, as well as viewpoints against these claims.[2]

            In favor of the Roosevelt administration using public opinion to fuel a war that FDR saw inevitable, Darnton states the theory that if a U.S. president could manipulate or bypass public opposition in provoking or hurrying entry of the United States into a major war, and could survive politically, then this would deal a significant blow to democratic (and American) exceptionalism and would provide strong support for the international relations realist worldview. Although one case will not resolve one of the foundational debates in international relations scholarship, much is clearly at stake.[3] Darnton having published his work recently gives the author the ability to view history through many works spanning over fifty years, thus having more viable sources to explore for his interpretation of events. It is perceived by a reader that Darnton is less bias than many authors on the topic as he gives insight into different perspectives on sociological and political implications of US involvement through his research. He uses varying sources with alternate viewpoints to create a cohesive manner of research in his ideas, however he favors a political viewpoint over a militaristic approach.

            In contrast to academic opinion on this, author David Kahn, considered one of the leading historians in the field of military history, states that he felt the crumbling relations began when the US claimed the Philippines in 1898 and escalated in 1922 with the disarmament conference in Washington. This meeting was possible thanks to famed early cryptanalyst Herbert Yardley and his assistant’s ability to decode diplomatic messages from the Japanese that stated just how far Washington officials could push. However, as Kahn states, in 1929 Secretary of State Henry L. Stimson, believing that mutual trust worked best in international affairs, refused to expend State Department funds for cryptanalysis.

            When Yardley, out of work in the Depression, wrote an indiscreet book in 1931 revealing the inside story, Japanese officials lost face, the Japanese press fulminated, relations with the United States deteriorated–and Japan improved its diplomatic cryptosystems. Tokyo adopted machine ciphers more complex than the system employing simultaneous use of multiple codebooks that Yardley and his team had cracked.[4]

            Kahn claims that these events ushered in a point of no return for relations between Japan and the United States, and it was only by sheer luck that the US military began codebreaking when accidentally gaining a copy of a Japanese codebook in 1923. It would take the entirety of the 1930’s to break this codebook, and by this point it has been replaced by the Japanese with a new one. Kahn’s choice of introduction leads the way for his reader to understand the importance of the 1940 victory of breaking the Japanese PURPLE code, as well as how this pertained to the lack of information for Pearl Harbor. Kahn’s position that this coupled with the fact that by the fall of 1941 tension between Japan and the United States escalated, causing negotiations to all but end after an American demarche on November 26, the acceptance of whose demands would have required Japan to pull out of China and in other ways to reverse its foreign policy.

            This gave Japan no other alternative but to wage war with the United States. Kahn’s work is as comprehensive as it could be for its time, however being written such a short time after Pearl Harbor, Kahn was not privy to much information that has been released in recent decades. While Kahn attempts to remain unbiased, it is clear he feels that the United States lack of sufficient cryptanalysts were a primary cause for eventual war, the buckling relations between the United States and the Empire of Japan in preceding years put the nail in the coffin long before December 7th, 1941.

            Timothy Wilford, author of Decoding Pearl Harbor, takes an approach that US involvement relied heavily upon the readability of Japanese codes, having known Japan-American relations steadily eroded throughout the end of the 1930’s and into 1940. Wilford maintains that arguably the most important object of USN cryptanalytic effort in 1941 was the decryption and translation of Japanese naval messages transmitted by radio, and through various primary and secondary sources available it is very unlikely the US had much warning, if any, that the Japanese would attack Pearl Harbor. Wilford states that new evidence released by the National Archives II in College Park, Maryland, sheds light on the controversial question of how well the USN could read Japanese naval traffic in late 1941 in that on the eve of Pearl Harbor USN cryptanalysts could partially read JN-25B, a code in which the Japanese transmitted numerous messages suggesting their intention to conduct a trans-Pacific raid against anchored capital ships.[5]

            Wilford aligns with many of Kahn’s analysis, and quotes Kahn’s work, The Codebreakers, explaining that the Japanese never sent any encoded messages revealing their intentions at Pearl Harbor: Why, then, did it cryptanalysis not prevent Pearl Harbor? Because Japan never sent any message saying that they would directly attack specifically Pearl Harbor.[6] However, Kahn also states in this work that Admiral Husband E. Kimmel, Commander in Chief of the Pacific Fleet, received enough MAGIC intercepts by late November1941 to know that war was possible, but emphasized that any forewarning of the Pearl Harbor attack was not possible.[7] Kahn would echo another of his works when theorizing that the cause of Pearl Harbor was due less to Japanese superiority in their codes and more to the US inferior cryptanalysts abilities.

            Wilford furthers his like-minded analysis by quoting Rear Admiral Edwin Layton stating that USN intercepts of Japanese radio traffic had potential intelligence value as clues to Japan’s operational intentions, including indications that an attack force of carriers was heading for an unknown target.[8] Layton offered no clear indication of how much information USN cryptologists gleaned from these intercepts of Japanese traffic, other than explaining that such traffic was 10% readable in 1941.[9] However, Wilford offers contrasting perspective by analyzing authors , James Rusbridger and Eric Nave who claimed British intelligence received enough decrypts from he Japanese codes to predict Pearl Harbor, which the US could not. They theorized Churchill knew of a possible long-range attack on the US and did not share this with Roosevelt. Wilford states that Rusbringer and Nave showed some misunderstanding of the JN-25 Japanese naval code as they failed to delineate the “A” version of the code from the later “B” version, and confused code types (encipherment) with additive types (superencipherment).[10] Wilford states that while these authors had certain letters to support a few claims, their findings were largely unsupported.

            Wilford, having access to newly released primary documents and exchanges with Allies during the early part of 1941 gives advantage over many authors who came before. Wilford also, as a result of this available information, clearly shows less bias than earlier historians of the early after war years. Objectivity is presented more than Kahn’s work in that Wilford attempts to offer multiple perspectives for interpretation of US involvement.

            Justus Doenecke is an American professor, historian and author who has won the Herbert Hoover Book Award or his contribution to American history. During his essay, Doenecke refers to varying historiographies of the period of his work. He also states his attempts to create his work to harmonize with other historiographical essays being published at the same time as this essay. Doenecke’s work focuses on current trends, as of its publishing date, in the historiography of the period, with particular attention to US policies between September 1939 with the invasion of Poland and the Japanese attack on Pearl Harbor.[11] Doenecke states early historians on foreign policy claimed Roosevelt himself was at the center of issue. Although much of the attack on FDR centered on his supposed complicity in the Pearl Harbor attack, his critics connected his European policy to the crisis with Japan.[12]

            Doenecke states how easily these perceptions penned historians against one another in bitter dispute. To comprehend much of the bitterness of this fight, one fact must be noted. The first historiographical battles usually involved individuals who had themselves often participated in the original Great Debate over Roosevelt’s foreign policy.[13] Doenecke states that most historians who addressed themselves to American policy in 1939-1941 could be placed in either the Roosevelt or the anti-interventionist categories.[14] However, this was ended during the 1960’s as many higher education institutions were teaching those who at best remembered World War II as a distant childhood memory. Doenecke also points out that many historian’s perception that Roosevelt often waited for events to unite citizens, such as his handling of the military draft and the lend-lease bill in 1940.[15] Doenecke leans very heavily toward attempting to remain unbiased in his work, and as such examines political and social aspects of the argument over United States involvement before and after Pearl Harbor. He paints a picture of divided politics, an isolationist nation reeling from domestic issues as well as horrific memories of World War I. His work is thorough, and unlike many other historians of the subject, does not limit his work to the interactions of Japan and the United States, but also includes relations with Europe.

            Often controversial, yet popular, contemporary author Ronald Spector presents a look at United States relations with Japan in regard to his interpretation on the United States joining global warfare. Spector’s choice of comment that “frequently army and navy leaders discussed the possibility of Japanese attack, in the final analysis it appeared unlikely, almost fantastic”[16] presents a military that did not view war as a possibility, directly contradicting Kahn in his assessment that military leaders such as Kimmel knew the plausibility of war with Japan. Spector tends to use a sense of grandeur in his work, and while informative in the basic sense there is a high level of bias in his tone and word choice when speaking of the grand display of United States naval power. Spector, while speaking of strained relations prior to Pearl Harbor, maintains the impression that war began with Pearl Harbor on December 7th, 1941. Though not my favorite work on the subject, Spector does present his impression tactfully, though his writing is a bit bland.

            In a direct contrast to Spector and his pull toward the Pacific being of utmost importance as it related to the war, Russian author Mikhail Suprun credits the lend-lease act as quietly involving the United States in the European theater before the Japanese ever attacked Pearl Harbor. This unofficial involvement poised what Suprun calls a “Germany first” strategy, meaning the European Theater of Operations took priority in comparison with all the other theaters, including the Pacific theater.[17] Suprun maintains the Allies agreed that ‘Germany-first’ was the dominant strategy for all participants of the coalition until the fall of Berlin in May 1945.[18] As such, Roosevelt’s “Lend Lease Act” allowed for the United States to supply ammunitions, supplies, rations and airplanes to the Allies without officially violating the United States’ position of neutrality in January 1941. Suprun states this is of importance to note because his concept — which could be called ‘America participating in the war without taking part in the action of warfare’ (or ‘Proxy War’) — was in effect until December 1941, when the USA were attacked by Japan. Roosevelt promised American mothers that their sons ‘will never be involved in the warfare in the interests of someone else’.[19] While this was acceptable at the time, the United States clearly aided allies such as Britain and France, thus Japan and Germany saw this as direct participation. The attack on Pearl Harbor put the USA in an equal situation with all other struggling nations and once Japan attacked, Germany declared war on the United States the following day.[20]

            While Suprun shows a slight bias toward his views on Russian participation, his analysis of the Lend-Lease interactions is straightforward. He does not offer much to opinion when discussing the general idea of the act itself, though is adamant that the allies, including the US, were apt to defeat Germany over all others, which is direct in contrast of many American authors who take special consideration on the Pacific theater being the main focus of the United States.

            John Thompson is the established author of the article Conceptions of National Security and American Entry into World War II, who theorizes involvement in World War II can be summed up as “defensive realism”. He discusses American position on foreign policy best seen by examining Franklin Roosevelt’s policy statements, arguments made by groups for and against involvement, and public opinion that indicated that feelings of national insecurity had less to do with American support for the Allies in the war than other factors.[21] Thompson even calls the US involvement in World War II the great turning-point in the history of U.S. foreign policy.[22] His position of the United States, while remaining officially neutral, devoted a grand portion of its resources to Great Britain selected her as a target long before Japan bombed Pearl Harbor. He also shares his thoughts of the United States remained isolationist due to insecurity about Atlantic defenses. Thompson claims United States repudiated the tenets of “isolationism” and threw its weight into the scales against the Axis powers (at the risk of war) because of fears for the nation’s own physical security.[23] His point maintains the United States aided the Allies for self-preservation, thus assistance such as the Lend Lease Act discussed by Suprun were in direct self interest and not out of goodness. While the bias in this analysis is evident, it does not seem to take away from the general work presented by Thompson in his political assumptions.

            While these sources present themselves adequately in terms of interpretive information of the period, I cannot help but feel they are lacking in social understanding. We know the American people did not favor another war in Europe, and many considered it Europe’s problem, we also know there was opposition to that thought process in both civilian and government sectors. However, it is important to note that their positions are not widely discussed. In addition to this, it is stated that Americans were not widely aware of the exact nature of the heinous events occurring in Europe, and many considered what little news that did come as an exaggeration. In our age of information such instance could not easily occur today, however the sheer thought that it is plausible begs the further understanding and study of how an entire nation could continue to support an isolationist ideal.

            When researching this topic, I made note that many sources focus on separating United States involvement by theater. My sources focus primarily on the Pacific theater or European theater respectively, but do not tend to interpret the correlation of the two. It is important to understand how one affected the other, and current research is lacking in this area due to, what I feel is a hyper focus on Pacific theater strategy. I feel that in order to truly understand the early involvement of United States participation in World War II, we must thoroughly expand our understanding of both the European and Pacific theater, and their effect on one another in a cohesive manner.

            Each of these historians collectively convey their interpretations in a manner befitting their period. While their interpretations vary in terms of argument, each collectively agree that official war began with Pearl Harbor, however the United States contributed through unofficial ways such as Suprun’s discussion of the Lend Lease Act, and Doenecke’s analysis of Roosevelt’s foreign policies of neutrality. However, when takin in consideration of bias being explicitly evident, such as in Spector’s Eagle Against the Sun, it is evident that even with recent works historians let bias cloud overall perceptions. If we are to excel as historians, we must strive for non-bias approach in our works.

            While not a historian, Yeoman Vincent DeCook shares his experiences as a shipman on the USS Minneapolis, beginning in 1941. His story is told through his son-in-law, Kenneth Huck, an engineer from Iowa. With DeCook’s position being what it was, he was privy to information most others were not. It should be noted that personal diaries were not allowed at this period, and thus DeCook asked that should the USS Minneapolis be destroyed, the diary should go along with it. DeCook’s account shows that for him, war began on December 7th, 1941. DeCook states he was approximately twenty miles from Pearl Harbor when going on his watch, and he noticed smoke in the direction of Oahu. Shortly after, he states, the sky over Pearl Harbor and Hickam Field began filling with bursts of AA (antiaircraft) fire.[24] He continues that confusion was evident, but at 2:20pm their radio stated that Japan had declared war on the United States and Great Britain. DeCook was just one of many who’s position remained war began when Japan attacked Pearl Harbor, as it did for many other servicemembers and civilians, as most were not privy to government policies at the time.

            During the early aftermath of the war, many historians were quick to dispel any question of the United States deploying the atomic bobs on Hiroshima and Nagasaki. It was a continued thought that it lessened the loss of life to do so, however this was before the effects of atomic warfare were understood. As time passed, and the war became a distant childhood memory for many, study began on the effects of atomic radiation and controversy of the use of atomic bombs remains to this day. Historians of the after-war period had personal accounts of those servicemen and women, however personal accounts are doomed to be just that: One person’s perceived story. It is only with a well-rounded, complete picture that one can truly write a lesser-biased historiography. Present day historians are fortunate to have many documents for study that earlier historians were not privy to, thanks to continuously released material by the parties involved.

            By studying these works, along with past historian’s works, we gain a better understanding of events such as wars, political situations, and cultures of the period. By researching historiographical works, we gather not only opinions of other historians, but a better understanding of our own writing. We perceive historical works not as facts, but rather an interpretation of how that author understood those facts.


Darnton, Christopher. 2017. “Archives and Inference Documentary Evidence in Case Study Research and the Debate over US Entry into World War II.” INTERNATIONAL SECURITY 42 (3): 84. doi:10.1162/ISEC_a_00306.

Kahn, David.(Winter 1991/1992. “The Intelligence Failure of Pearl Harbor,” Foreign Affairs 70.5: 144, 147.

Wilford, Timothy. 2002. “Decoding Pearl Harbor: Usn Cryptanalysis and the Challenge of Jn-25B in 1941.” Northern Mariner / Le Marin Du Nord 12 (1): 17–37.

Doenecke, Justus D. 1995. “U.S. Policy and the European War, 1939-1941.” Diplomatic History 19 (4): 669. doi:10.1111/j.1467-7709.1995.tb00670.x.

Spector, Ronald. 1985. Eagle Against the Sun. New York: Random House.

Suprun, Mikhail N. 2019. “Lend-Lease and the Northern Convoys in the Allied Strategy During the Second World War.” Journal of Slavic Military Studies 32 (4): 574–80

Thompson, John A. 2005. “Conceptions of National Security and American Entry into World War II.” Diplomacy & Statecraft 16 (4): 671–97.

DeCook, Vincent Evo, and Kenneth W. Huck. 2010. Log of World War II: a Pacific Naval Diary. Bloomington, IN: Xlibris.

[1] Darnton, Christopher. 2017. “Archives and Inference Documentary Evidence in Case Study Research and the Debate over US Entry into World War II.”

[2] Ibid.

[3] Ibid.

[4] Kahn, David. Winter 1991/1992. “The Intelligence Failure of Pearl Harbor,” Foreign Affairs 70.5: 144, 147.

[5] Wilford, Timothy. 2002. “Decoding Pearl Harbor: Usn Cryptanalysis and the Challenge of Jn-25B in 1941.” P.18.

[6] Kahn, David. The Codebreakers, 10.

[7] Ibid.

[8] Wilford, Timothy. 2002. “Decoding Pearl Harbor: Usn Cryptanalysis and the Challenge of Jn-25B in 1941.” P.22

[9][9] Ibid.

[10] Ibid.

[11] Doenecke, Justus D. 1995. “U.S. Policy and the European War, 1939-1941.”

[12] Ibid.

[13] Ibid.

[14] Ibid.

[15] Ibid.

[16] Spector, Ronald. 1985. Eagle Against the Sun. New York: Random House.

[17] Suprun, Mikhail N. 2019. “Lend-Lease and the Northern Convoys in the Allied Strategy During the Second World War.”

[18] Ibid.

[19] Ibid.

[20] Ibid.

[21] Thompson, John A. 2005. “Conceptions of National Security and American Entry into World War II.” P1.

[22] Ibid.

[23] Ibid.

[24] DeCook, Vincent Evo, and Kenneth W. Huck. 2010. Log of World War II: a Pacific Naval Diary.

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