The Kidō Butai sails for Hawaii

On the morning of 26 November 1941, Tokyo time, a naval force such as the world had never seen put to sea from Hitokappu Bay on the island of Iturup – Etorofu in Japanese – in the chain of the Kuril Islands. Its core was six carriers of the Japanese navy, Akagi, Kaga, Sōryū, Hiryū, Shōkaku and Zuikaku, with more than 400 aircraft aboard. They were commanded by Vice-Admiral Chūichi Nagumo, commander of the First Air Fleet. The force, called the carrier striking force in Japanese documents and simply the Kidō Butai (“Mobile Force”) in staff parlance, steamed across the empty, stormy waters of the northern Pacific towards Hawaii. In twelve days its aircraft were to strike the US Pacific Fleet at Pearl Harbor (PL).

In Washington it was then the afternoon of 25 November. A few hours earlier President Franklin Delano Roosevelt had conferred with members of his cabinet and the chiefs of staff on how to respond to the latest Japanese proposals. According to the diary of Secretary of War Henry Stimson, the President remarked that the Japanese, notorious for attacking without warning, might strike as soon as the following Monday. Yet nobody in the American high command was thinking of Hawaii. All eyes were on the south, where Japan was massing transports and troops off the coast of Indochina.

The fleet is often described as consisting of 33 warships and auxiliaries. Japanese lists give slightly fewer: six carriers, two fast battleships, two heavy cruisers, a light cruiser with nine destroyers, three submarines and seven tankers sailed from Hitokappu, thirty vessels in all. An American monograph compiled after the war from the accounts of Japanese officers lists eight supply ships. The higher figures result from different ways of counting, for example by including the two destroyers and a tanker that sailed separately to bombard Midway atoll.

Yamamoto’s plan

The idea of striking the American fleet in its base was the work of one man: the commander of the Combined Fleet, Admiral Isoroku Yamamoto. A former naval attaché in Washington, Yamamoto regarded war with the United States as madness, for he knew the superiority of American industry. But since the government was heading for that war, he wanted to open it with a blow that would knock the American fleet out for many months and allow Japan to seize the colonies to the south, rich in oil and rubber, without interference. The navy’s old doctrine envisaged the opposite: to wait for the Americans to come across the Pacific, wear them down on the way with submarines and aircraft, and then fight a decisive battleship engagement in waters close to Japan. Yamamoto believed that such a plan had not worked even in war games.

On 7 January 1941 he set out his idea in a letter to the Navy Minister, Koshirō Oikawa. One of the stimuli was the British attack on Taranto in November 1940, in which torpedo bombers from a single carrier had torpedoed three Italian battleships in harbour. Yamamoto may also have had a native precedent in mind: in February 1904 Japanese torpedo boats had attacked the Russian squadron at Port Arthur without a declaration of war, opening the Russo-Japanese War. In the spring a draft of the operation was prepared by Lieutenant Commander Minoru Genda, a naval aviator, at the request of Rear Admiral Takijirō Ōnishi. On 10 April 1941 the First Air Fleet was formed, concentrating the carriers in a single formation instead of dividing them among the battleship squadrons. Command went to Nagumo, a senior admiral and a torpedo specialist rather than an aviator, who was sceptical of Yamamoto’s plan.

The Naval General Staff resisted for a long time. Its officers considered a strike on Hawaii a gamble: the force might be discovered on the way, and the carriers would then be missing in the south, where the war was to be decided. In a war game in September 1941 the umpires ruled that the Japanese would lose some of their carriers in the attack. The dispute was settled only in October, when Yamamoto’s emissary, Captain Kameto Kuroshima, declared in Tokyo that if the plan were not adopted with all six carriers, the admiral would resign. The Chief of the Naval General Staff, Admiral Osami Nagano, gave way.

Torpedoes in shallow water

The hardest problem was a technical one. The harbour at Pearl Harbor was only about twelve metres deep, while an ordinary aerial torpedo, once dropped, dived much deeper and stuck in the bottom. The British had solved the problem at Taranto in their own conditions; the Japanese had to find their own solution. Their Type 91 torpedoes were fitted with wooden fins that limited their dive, and from the autumn the pilots of Nakajima B5N aircraft practised drops from very low altitude over Kagoshima Bay on Kyushu, whose shape resembled Pearl Harbor. The last batches of modified torpedoes reached the carriers literally at the last moment. Because some of the American battleships were moored in pairs alongside Ford Island, so that torpedoes could not reach the inboard ships, 410 mm armour-piercing shells were converted into 800 kg aerial bombs to be dropped from high altitude.

The airmen’s training was directed by Commander Mitsuo Fuchida, appointed to lead the whole strike, while the torpedo bombers were trained by Lieutenant Commander Shigeharu Murata. For a long time the crews did not know what they were preparing for. Knowledge of the harbour, the berthing of the ships and the fleet’s routines was supplied by naval intelligence, above all by Takeo Yoshikawa, who from March 1941, under cover as a consulate clerk, kept Pearl Harbor under observation. In early November naval officers disguised as members of a passenger liner’s crew collected maps in Honolulu, together with answers to a list of detailed questions.

From 5 November to Hitokappu

The political decisions were taken in early November. The Imperial Conference of 6 September had determined that if negotiations with the Americans failed, Japan would go to war. When in October Hideki Tōjō replaced Prince Konoe as prime minister, the new government reviewed the whole policy once more but reached the same conclusion. On 3 November the chiefs of staff presented the operational plans to Emperor Hirohito, including the strike on Hawaii on 8 December, Tokyo time, and the Imperial Conference of 5 November adopted a new “Essentials for Carrying Out the Empire’s Policies”: if no agreement had been reached by 1 December, Japan would go to war with the United States, Britain and the Netherlands, and preparations were to be completed by early December. On the same day the Naval General Staff issued its order for war preparations, and Yamamoto circulated Combined Fleet Operation Order No. 1, which set out the entire plan for the war at sea. The diplomat Saburō Kurusu set off for Washington with the final proposals.

The dates were chosen with care. 8 December in Tokyo was Sunday 7 December in Hawaii, the day on which the American fleet was most often in harbour and its crews on leave. The navy also pressed for no delay: with every week the weather in the northern Pacific would worsen and refuelling at sea would become harder.

From mid-November the ships left their bases in the Inland Sea and on Kyushu singly and in small groups so as not to attract attention. According to the Japanese official history of the operation, on 17 November Yamamoto visited Akagi in Saeki Bay and told the officers that the success of this operation would determine the fate of all those that followed. According to Japanese accounts, radio operators remained behind in the Inland Sea and sent routine signals so that enemy listeners would believe the carriers were still in their bases. By about 22 November the whole force had assembled in Hitokappu, a remote bay that did not freeze in winter, surrounded by a few fishing settlements. The island’s telegraph link with the outside world was cut and the inhabitants were forbidden to approach the shore. Aboard Akagi, Nagumo and his chief of staff, Rear Admiral Ryūnosuke Kusaka, explained the purpose of the expedition to the ship captains; only now were the crews told. On the basis of a Naval General Staff order of 21 November, Yamamoto ordered on 25 November that the force should sail in the utmost secrecy the next morning and reach a waiting point at 42° North and 170° West by 3 December, where it was to refuel.

A voyage under radio silence

The route was chosen to avoid shipping lanes and the areas patrolled by American aircraft from Midway and the Aleutians. In November the northern Pacific was empty and stormy, and fog and low cloud gave the ships further cover. The price was fuel: only some of the ships had the range to sail from the Kurils to Hawaii and back without refuelling, so drums of oil were stacked on the carriers and in every free corner of the destroyers, and refuelling from tankers in heavy seas was hard and dangerous work.

The force sailed under complete radio silence. Transmitters were sealed, and on some ships their fuses were removed. The ships could receive signals from Tokyo but could send nothing, and communication between them was by flags by day and signal lamps by night. A complete blackout was enforced, and no rubbish could be thrown overboard lest it leave a trail. Three submarines sailed ahead to give warning of any ships encountered. Under the orders, discovery many days before reaching the target could mean turning back, but discovery within the last day before the strike did not release the force from its duty to attack.

At the same time more than twenty large submarines of the Sixth Fleet were heading for Hawaii to surround the island of Oʻahu and attack ships escaping from the harbour. Five of them carried Ko-hyoteki-class midget submarines, which were to penetrate Pearl Harbor itself. Simultaneously, most of the rest of the Japanese fleet was leaving its bases, together with convoys carrying troops for landings in Malaya, the Philippines and elsewhere in South-East Asia.

The recall clause

Nagumo’s expedition was not yet an irrevocable decision for war. The order of 25 November stipulated that if negotiations with the United States ended in agreement, the force would turn back home at once. According to accounts collected after the war by the American historian Gordon Prange, when some officers at a commanders’ conference at Iwakuni on 13 November protested that turning back at the last moment, with aircraft ready to take off, would be unbearable, Yamamoto replied that any commander unable to carry out such an order should resign at once. Japanese memoirs also mention an agreed signal cancelling the attack, but its wording is uncertain.

In Tokyo such a possibility was purely theoretical. The Tōjō government had no intention of yielding over its troops in China, and Kurusu, who reached Washington on 15 November, brought proposals that the Americans considered unacceptable. On 20 November the ambassador, Admiral Kichisaburō Nomura, and Kurusu presented the last of them, the so-called Plan B, to Secretary of State Cordell Hull: Japan would withdraw its troops from southern Indochina, and in return the United States would restore the oil supplies cut off in the summer and stop helping China. The Americans, who thanks to breaking the Japanese cipher were reading the correspondence between Tokyo and the embassy, also knew that on 22 November Foreign Minister Shigenori Tōgō had moved the final deadline for the negotiations to 29 November, adding that after that “things are automatically going to happen”. They did not know what exactly was to happen then. The diplomatic signals said nothing of the navy’s plans, and the Americans were not yet breaking its operational codes.

About 25 hours after the force left Hitokappu, Hull handed Nomura and Kurusu an American note demanding the withdrawal of Japanese troops from China and Indochina. In Tokyo it was regarded as an ultimatum and as proof that further negotiations were pointless. By then Nagumo’s ships were already on the open sea.

What was seen at Pearl Harbor

At Pearl Harbor Admiral Husband Kimmel, who had commanded the Pacific Fleet since February, had no idea of the Japanese force. The radio intelligence officers in Hawaii who tracked Japanese call signs lost contact with the carriers at the end of November. In their assessment the carriers were in their home ports and using land lines, as had happened before. According to the memoirs of the fleet intelligence officer Edwin Layton, when on 2 December he admitted that he did not know where two Japanese carrier divisions were, Kimmel asked him ironically whether they might be rounding Diamond Head, the headland at the entrance to Honolulu, at that very moment. Later claims by some authors that American listening stations picked up signals sent by the force on its way have found no confirmation in the documents and are rejected by most historians.

Warnings from Washington did come, but they pointed in another direction. On 27 November the Chief of Naval Operations, Admiral Harold Stark, sent Kimmel a signal that was to be considered a “war warning”. It named the Philippines, Thailand, the Kra Isthmus and Borneo as likely targets of a Japanese offensive.

Climb Mount Niitaka

On the evening of 2 December, Tokyo time, a day after another Imperial Conference had formally decided on war, the staff sent Nagumo’s force the signal “Niitakayama nobore 1208” – “Climb Mount Niitaka 1208”. Niitaka, today’s Yu Shan in Taiwan, was then the highest mountain in the empire, and the number stood for 8 December, the date of the attack. The force, which had reached the waiting point on 3 December and refuelled, turned south-east and then south. After the last refuelling the tankers detached, and the warships made at high speed for the launch point, some 230 nautical miles north of Oʻahu.

On the morning of 7 December 1941, Hawaiian time, two waves of aircraft, some 350 machines in all, took off from the carriers, led by Fuchida. The strike sank or damaged eight battleships of the Pacific Fleet, destroyed nearly two hundred aircraft and killed more than 2,400 Americans. The Japanese lost twenty-nine aircraft. The three American carriers, however, were not in harbour, and Nagumo, not knowing where they were, did not repeat the attack against the dockyard and the fuel tanks but turned back for Japan.

Place in the war

The departure of the Kidō Butai from Hitokappu was the moment at which Japan’s decision for war became executable. The political decisions of 5 November and 1 December still left a door open for diplomacy, but from 26 November the most powerful carrier force in the world was steaming towards an American base, and every day of the voyage made turning back harder. Neither orders from Tokyo nor the secrecy of the talks in Washington changed its course.

Nagumo’s expedition was also a new form of naval warfare. Six carriers concentrated in a single force, moved in secret across half an ocean and striking with aircraft from a distance of several hundred kilometres, showed that it was carrier aviation, not battleships, that decided command of the sea. The Americans, whose battleships Pearl Harbor had taken away but whose carriers it had spared, drew the lessons faster than the Japanese themselves. Half a year later, in June 1942, four of the six carriers that had sailed from Hitokappu were sunk at the Battle of Midway.

The attack itself, delivered without a declaration of war, united Americans in the will to fight on to total victory over Japan. A few days later Adolf Hitler declared war on the United States, and the war in Europe and the war in the Far East became a single world war. Yamamoto, who had feared such a turn of events, predicted that Japan would win victories for the first six months or a year, but was not confident about the years that followed. Richard Sorge, arrested in Tokyo in October, had still managed to inform Moscow that Japan would not attack the Soviet Union but would go south. The Kidō Butai’s expedition confirmed that report, although Sorge could have known nothing of the strike on Hawaii itself.