Why Did Japan Attack Pearl Harbor?

This is a guest post by Dave HackersonA previous post in this series is can be found here.

The International Dateline is truly a fascinating thing. It’s like a magic wand of time that can both give and take, depending which way you head. Each time my family and I fly back to the Midwest, the space time continuum is seemingly suspended. Leave Tokyo at 4:00 pm, touch down in the Midwest at 2:00 pm, and then reach our final destination by 5:00 pm of the same day. Over 15 hours of travel that appears to have been compressed within the span of one single hour. I still can’t wrap my head around it at times.

This dateline has a way of slightly altering our perspective of historical events. Most Americans are familiar with the following quote from President Franklin Delano Roosevelt: “December 7th, a date that will live in infamy.” The date to which he refers is the day on which the Combined Fleet of the Japanese Imperial Navy under the command of Admiral Isoroku Yamamato attacked the elements of the US Pacific fleet at Pearl Harbor. However, this is the narrative from the American side of the International Dateline. The December 24th edition of Shashin Shuhou (Photographic Weekly), a morale boosting propaganda magazine published in Japan from the 1938 until mid-1945, carried the following headline for its graphic two-page artist’s depiction of the attack: “Shattering the dawn: Attack on Pearl Harbor, December 8th”. The Japanese government christened the 8th day of each month as Taisho Hotaibi (literally means “Day to Reverently Accept the Imperial Edict”) to commemorate the great victory over the United States at Pearl Harbor and the Imperial declaration of war on the US and its allies (the day also served to regularly renew nation’s fervor and commitment to the war effort). Was Pearl Harbor a great victory for the Japanese? The answer to this question depends on the context in which the attack is viewed. From a purely military engagement view, it is safe to say that it was a resounding success, but did this single engagement succeed in shaping the course of the upcoming conflict? This is the question that the Mainichi Shinbun explored in the third installment of its series “Numbers tell a tale—Looking at the Pacific War through data” (the original, in Japanese, is here). True to the narrative on this side of the Pacific, this article was released on December 8th last year. Just as with the other installments in the series, it presents a slew of data that helps to put historical events into context.

“Did the attack on Pearl Harbor truly break the US? Japan’s massive gamble with only a quarter of the US’s national strength.” The title of the article does a nice job of setting up the exhaustive economic analysis it conducts in an attempt to answer this question. The very first thing the article does is to compare the respective GDPs of the US and Japan in 1939. At this time, Japan’s GDP stood at 201.766 billion dollars. However, this amounted to less than a fourth of the US’s GDP of 930.828 billion dollars (note that figures are not adjusted for inflation). Even the UK had a larger GDP than Japan at 315.691 billion dollars. When you combine the GDPs of the US and UK, Japan already suffered a disadvantage of greater than 6 to 1.

The next set of figures the article introduces is related to industrial capacity. The first thing it examines is iron production, and here the article makes reference to the quote by Prussian leader Otto Van Bismarck, who claimed that it was iron which made a nation. Taking Bismarck at his word, Japan’s iron production did not bode well for its position as a nation. In 1940, Japan’s national production of crude steel was 6,856,000 tons per year. In contrast, the US was producing nearly nine times that amount at 60,766,000 tons per year. Likewise, Japan lagged far behind the US in terms of electric power output and automobile ownership. Japan’s electric power output in 1940 stood at 3.47 billion kWh, but this figured was dwarfed by the US’s output of 17.99 billion kWh. The gap in automobile ownership is also especially telling. The 1920s are often considered to be the decade in which America “hit the roads” and became enamored with the automobile, and this fact is backed up the figures for automobiles owned by Americans in 1940. By that year, there were already 32,453,000 automobiles on roads in the US. Japan didn’t even come close, with only 152,000 automobiles scattered across the country.

In addition to lacking the physical resources and infrastructure to sustain a prolonged war of attrition, the makeup of Japan’s economy also posed a number of difficulties. Here the article emphasizes a major difference between Japan and other first world nations at that time: Japan was not a “heavily industrialized nation”. This fact was clearly reflected in the country’s exports. In 1940 finished metal products accounted for only 2.8% of the nation’s exports, while raw silk, textiles, and clothing products made up for more than a quarter. Likewise, only 30% of the nation’s income was generated by industry, which was less than the combined income of agriculture, retail, and transport sectors. In the 1930s, Japan made every effort to expand its heavy industries. The Truman administration dispatched an investigative committee to Japan after the war to study the effects of America’s strategic bombing on Japan and its economy. The study found that in 1930 the industrial makeup of Japan was 38.2% heavy industry and 61.8% light industry. By 1937 Japan had succeeded in reversing these percentages to 57.8% and 42.2%, but the difficulty the nation had in securing the resources it needed for industry restricted its industrial capacity. The study did not mince words in its assessment of the Japanese economy. “The nation of Japan is truly a small country in every manner of speaking, and ultimately a weak nation with an industrial infrastructure dependent on imported materials and resources, utterly defenseless against every type of modern-day attack. The nation’s economy at its core was rooted in a cycle of daily subsistence, in which people only produced what they needed for that day. This left it with no extra capacity whatsoever, leaving it incapable of dealing with potential emergencies that may arise.”

To compensate for its lack of resources, Japan cast its gaze across the waters to Manchuria. Japan had steadily expanded its interests in Manchuria since its victory in the Russo-Japanese War in 1905, and placed the South Manchuria Railway Company as the primary driver of this massive undertaking. This company was founded in 1906 upon the railway Japan received from Russia after the war, and was a national policy concern that was half-owned by the state. Japan aimed to make Manchuria the focal point of an own economic bloc that also included Korea, Taiwan, and China. While Manchuria was rich in natural resources, it was highly underdeveloped, and Japan ultimately exported far more machinery and infrastructure building equipment than the resources it imported. While Japan was able to construct some of this machinery and equipment on its own, it was dependent on material and machine-related imports from the US, UK, the Netherlands, and Australia, the very nations against which it would ultimately go to war. In 1930, Japan exported nearly 96% of its raw silk thread to the US, which would send raw cotton back the other way. Japan would then process this cotton into finished cotton products for export to British India and the UK. Using the profits from these exports, Japan would then import strategic resources from the US, UK, and the Netherlands, such as oil, bauxite to create the aluminum used in air craft, and the bronze needed for the metal casings of bullets. The problematic nature of these trade relationships was pointed out by the Japanese economist Toichi Nawa of Osaka University of Commerce (present-day Osaka City University). In his book Research on the Japanese Spinning Industry and Raw Cotton Problem, Nawa stated that “any confrontation with the UK and US would be tragic, and must be avoided.” He further elaborated on Japan’s trade issues, saying that “the more Japan rushes along its efforts to expand heavy industry and its military industrial manufacturing capacity so it can bolster its policies on the continent (Manchuria and China), the more dependent it becomes on the international market, creating cycle that leads to increased imports of raw materials. Herein lies the gravest of concerns for the Japanese economy.”

Nawa’s words proved to be all too prophetic. Japan’s aggressive agenda in China following the Marco Polo Bridge incident in 1937 brought heavy criticism from the global community. As the conflict in China escalated, Western nations retaliated with economic sanctions and restrictions on imports. The most devastating of these was the US’s decision to ban all oil exports to Japan in August of 1941. The US was the world’s largest producer of oil in 1940, accounting for over 60% of the world’s supply. The upper brass of the Imperial Japanese Navy had predicted that they had enough oil stockpiled to wage war for at least 2 and half years, but if the UK and US shut off all oil exports, they would have no other choice but to move into Dutch territory and seize the oil fields of within 4 to 5 months in order to augment their supply. The attack on Pearl Harbor occurred exactly four months later.

Did Japan truly have the capacity as a nation to wage a modern war against a nation such as the United States? As tensions rose in US-Japan relations, Japanese government and military officials took a hard look at the data available in an attempt to answer this question.

A joint military and civilian economic study group organized around army paymaster Lt. Colonel Jiro Akimaru was set up in February 1941 to undertake this task. Known as the “Akimaru Agency”, this group was split into four sections to study the total war capacity of Japan, the UK-US, Germany, and the Soviet Union. The report they compiled by the end of September 1941 made the following conclusions:

1)      The conflicting state between Japan’s military mobilization and its labor force has become fully evident. Japan has also reached its peak production capacity, and is unable to expand it any further.

2)      Germany’s war capacity is now at a critical point.

3)      Not a single flaw exists within the US’s war economy.

Even if Japan sacrificed the living standards of its populace to boost its war capacity, it still would not have the financial resources to compete with the US. Hiromi Arisawa, a member of the UK-US section who was also president of Hosei University during his lifetime, made the following remarks when reflecting back on the report the Akimaru Agency prepared:

“Japan cut national consumption by 50%. In contrast, America only reduced its national consumption by 15 to 20%. Excluding the amount of supplies they shipped to other Allied nations at that time, the savings from this reduced consumption provided them with 35 billion dollars* for real war expenditures. That was 7.5 times greater than what Japan was capable of achieving with its cuts.”

Lt. Colonel Akimaru alluded to this fact when he presented the report at an internal staff conference meeting for the Army. Gen Sugiyama, Chief of Staff of the Supreme Command, acknowledged that the report was “nearly flawless” in its analysis. After praising Akimaru for the quality of the report, he then issued the following order. “The conclusion of your report goes against national policy. I want you to burn every copy of it immediately.”

Lt. Colonel Hideo Iwakuro, founder of the Nakano School and a military intelligence expert, was dispatched to the Japanese embassy in the US and took part in the planning of unofficial negotiations between the two countries. He returned to Japan in August of 1941 and met with influential figures in the political and business world, trying to persuade them of the futility in war with the US. At the Imperial General Headquarters Government Liaison Conference, Iwakuro presented the following data based on his own personal research to demonstrate the gap between the US and Japan in terms of national strength.

Iwakuro’s conclusion was straight and to the point. “The US has a 10-1 advantage in terms of total war capacity. All the Yamato-damashii (Japanese fighting spirit) we throw at them will not change anything. Japan has no prospects of victory.” Incidentally, the next day War Minister Hideki Tojo (who later became Prime Minister) immediately ordered the transfer of Iwakuro to a unit stationed in Cambodia. Iwakuro made the following remarks to the people who came to see him off at Tokyo Station. “If I should survive this ordeal and ever make it back to Tokyo, the Tokyo Station we see here will most assuredly lie in ruins.” Those words came to fruition in the spring of 1945.


Admiral Yamamoto salutes Japanese pilots.
Admiral Yamamoto salutes Japanese pilots.


So did the attack on Pearl Harbor truly break the US? The quote made by Admiral Yamamoto at the end of the movie Tora! Tora! Tora! puts it quite succinctly: “All we have done is to awaken a sleeping giant and fill him with a terrible resolve.” Though there is debate about whether he actually uttered those words, Yamamoto was no stranger to the US having studied at Harvard and spending time as a naval attache, and he knew full well the awesome industrial might and material resources the nation possessed. Japan played a great hand with its attack on Pearl Harbor, but as Yamamoto knew, the deck was already stacked against it. The only thing that remained to be seen was how long Japan could make its kitty last.