Japan Thought Pearl Harbor Would Destroy the U.S. Navy (What a Mistake)

September 18, 2019 Topic: History Region: Asia Blog Brand: The Buzz Tags: World War IIImperial JapanAmericaPearl HarborPacific Theater

Japan Thought Pearl Harbor Would Destroy the U.S. Navy (What a Mistake)

A big mistake.

The Blueprint For Pearl Harbor


In November 1940, with hostilities in Europe having broken out, Japan’s attention was captured by the surprise British raid on the Italian fleet anchored at Taranto. Although obsolescent, the British biplanes, operating from carriers, delivered a blow that sank or badly damaged three of the Royal Italian Navy’s modern battleships against a loss of just two planes.

The attack inspired Admiral Isoroku Yamamoto, commander in chief of Japan’s Combined Fleet, to begin thinking of how a similar attack––if war with the United States could not be avoided––could neutralize American military might in the Pacific. He began formulating a broad concept that would be a decisive, devastating katana thrust into the heart of America’s interests in the region––an attack against the U.S. Pacific Fleet in Hawaii and elsewhere.

To help refine the concept into a detailed, workable plan, Yamamoto called upon the advice and expertise of such officers as his chief of staff, Admiral Shigeru Fukudome; chief of the Japanese Naval Staff, Rear Admiral Osami Nagano; chief of staff of the XI Air Force, Rear Admiral Takijuro Onishi; and Commander Minoru Genda, a young, brilliant tactician and expert in naval aviation. For months the men discussed, argued, conceived, and discarded various ideas on how best to carry out such an attack—especially one that would require the undetected movement of a large fleet over vast distances.

Ironically, probably no one in Japan was more doubtful about a successful outcome than Yamamoto. In the 1920s, he had been a student at Harvard; later, he served as naval attaché in Washington. He knew firsthand the vastness of America’s industrial might and capacity; when it came to the ability to wage and sustain a long war over immense distances, America was the elephant, Japan the flea. His nation’s only hope was to strike such a crushing blow that America, left helpless and exposed, would be unable to prevent Japan from taking all the territory it wanted—or so the Japanese militarists believed—and would sue for peace.

Yamamoto was unconvinced that Japan could prevail in a protracted war. In a January 1941 letter to one of Japan’s arch-nationalists, he wrote, “Should hostilities break out between Japan and the United States, it would not be enough that we take Guam and the Philippines, nor even Hawaii and San Francisco. To make victory certain, we would have to march into Washington and dictate the terms of peace in the White House.”

Thus began a long, secretive process to launch a war that many (but not all) in Japan saw as “inevitable.” The planning went forward, and eventually a blueprint was drawn up.

The Collapse of Diplomatic Negotiations

To string the Americans along and make them think that peace was possible even while plans for war marched ahead, Japan sent a new ambassador, Kichisaburo Nomura, to the United States in February 1941 to engage in protracted negotiations with Secretary of State Cordell Hull that were little more than a smokescreen hiding his nation’s true intentions. Nomura himself was kept in the dark as to what those intentions were and dutifully carried out his assignment, believing that his efforts just might forestall all-out conflict.

In the summer of 1941, President Franklin D. Roosevelt persuaded Congress to freeze Japanese assets in the United States and shut off exports of oil and scrap iron, further infuriating Japan’s hard-liners. The militarists, led by General Hideki Tojo (who would become prime minister in October 1941), felt that only one course of action was open to them: war with the United States and the other Western powers—mostly the British, French, and Dutch—who had colonies in Asia and the Pacific.

But it was the United States that represented the most serious threat to Tojo’s goals of conquest and expansion. To neutralize American power and influence in the region—unless diplomatic moves resulted in the United States backing down from its “hostile attitude” toward Japan—Japan’s military leaders would have to seize the initiative and strike a blow from which America would have a difficult time recovering. It would be an immense undertaking, one that would require tremendous sacrifice and effort, and with no assurance of success.

If Japan were not allowed to trade freely with the West, Tojo argued, then Japan, which Tojo and his followers regarded as morally and racially superior to other cultures, would take the resources it needed. Tojo noted, “It goes without saying that when survival is threatened, struggles erupt between peoples, and unfortunate wars between nations result.”

Preparing Yamamoto’s Plans

With the failure of diplomacy almost a foregone conclusion, Tojo moved ever closer to launching a preemptive strike. While Japanese diplomats talked peace in Washington, a large naval task force would allow itself to be seen heading from Japanese home waters toward Southeast Asia—Malaysia, Singapore, Hong Kong, Dutch East Indies, French Indochina (today Vietnam), and Siam (today Thailand). Thus, while Western eyes were concentrating on this movement (and perhaps even moving assets there to counter any hostilities), another task force would secretly head north and east, aiming at Hawaii. A third force would target the Philippines, which were then an American territory. Swift and violent attacks would be used to decimate American military installations, ships, airfields, and warplanes.

Although racked with internal doubts and conflicts about what he saw coming, Yamamoto felt that as commander in chief of the Combined Fleet, he must obey orders and do his duty–—no matter how wrongheaded those orders were. In January 1941, he began looking for ways that Japan could inflict the greatest damage on the United States while suffering the least amount of pain.

Gradually the tactical concept took shape. A force of six aircraft carriers would steam through the often-stormy waters of the northern Pacific, doing its best to avoid any sea or air patrols.  About 200 miles north of Hawaii, the carriers would launch a combined aerial armada of torpedo planes, fighters, and bombers before dawn on a Sunday to catch the Americans at their most vulnerable; dawn attacks have always been the mainstay of military operations.

The attackers would arrive in several waves, each with a specific mission. Midget subs would inflict further damage, and fleet submarines would lurk near Oahu to sink any American ships found coming or going. With a divine grant of fortune, the American fleet would be crippled, American airpower destroyed, and American morale crushed, and within a matter of a couple of hours the attackers would return safely to their carriers, which would then slip away as secretly as they had arrived, safe from counterattack.

At last the Naval General Staff approved Yamamoto’s plan and pilots began training for their secret mission. As the British did before Taranto, the Japanese modified aerial torpedoes to work in the shallow waters of Pearl Harbor. Spies in Hawaii fed Japan with a steady stream of information about what ships were in harbor and where they were berthed.

While the physical assets were being assembled at naval bases across Japan, the personnel, too, were being selected and briefed on the ultrasecret operation. Commander Minoru Genda was named air officer in charge of the aerial assault. His friend, Lt. Cmdr. Mitsuo Fuchida, was appointed to command the First Air Fleet and would lead the initial wave to the target. Only Japan’s most skilled pilots would be chosen to take part.

A relentless period of training and exercises commenced for the aircrews at Kagoshima Bay in southern Kyushu, an area that bore a strong resemblance to Pearl Harbor. Using specially modified aerial torpedoes that would not lodge themselves in the bottom mud of shallow Pearl Harbor, the torpedo-bomber pilots practiced relentlessly. The dive-bombers and high-level bombers, too, dropped hundreds of dummy bombs to perfect their aim. After months of intense training, the Japanese carrier pilots were, without a doubt, the best-trained aviators in the world.

Breaking the Japanese Code

In the meantime, a flurry of messages flew back and forth between Hawaii and Washington, D.C. What the Japanese did not know was that in August 1940, after 18 months of trial and error, American cryptanalysts had finally broken Japan’s fiendishly difficult J-19 diplomatic code (known as “Purple”) by a protocol code-named “Magic.”

Despite this breakthrough, however, the Americans had not yet been able to decipher the codes for Japan’s Army and Navy, nor did many Purple messages lend themselves to easy interpretation—the “winds” messages, for example, which outlined various contingencies for going to war with either the United States, Great Britain, or the Soviet Union, were too obtuse to make much sense.

(After years of trying, the Japanese naval code, dubbed “JN-25” by the American cryptanalysts, was finally cracked in January 1942 by the Combat Intelligence Unit under the command of Commodore John Rochefort working in the basement of the 14th Naval District Administration Building at Pearl Harbor––with the aid of the rudimentary IBM ECM Mark III computer.)

Whenever a new diplomatic message was received, translated, and interpreted, the people at the War Department and Navy Department would send updates to Hawaii; what they thought were alerts and warnings of possible impending hostile action by the Japanese were often viewed by the commanders in Hawaii as being vague and inconclusive, full of unhelpful contradictions and unsupported conclusions. It was no wonder that General Short devoted most of his efforts to preventing sabotage at the island’s military facilities by the local Japanese population rather than preparing to repel an all-out aerial assault.