World War Two: Japanese Fleet; April 1940 to 6 December 1941

The possibility of war with the United states had long occupied the attention of the Japanese Naval Staff. The two most apparent choices open to them were either to assist the Army in its southern advance and await an American counterattack (possibly with British support), preferably in home waters; or to devise a surprise attack on the U.S. Pacific Fleet at the very outset. The proponents of the first measure cited the success at the battle of Tsushima Strait in the Russo-Japanese War. From what the Japanese knew of the Rainbow-5 plan, however, it was clear the United States would probably seek the conquest of the Marshall islands and the establishment of a forward bases there, and then leapfrog through the Carolinas and Marianas. If the Americans proceeded thus, an early decisive battle in Japan’s home waters would not occur; instead, the war would be prolonged, and the industrial capacity of the United States would prevail. Since a long war was what most Japanese naval men feared, they came to favor the idea of a decisive surprise attack, if an effective operation could be conceived.

Yamamoto had to devise an operation that would insure success with a minimum of risk. It was standard naval doctrine at that time a fleet could not operate successfully more than two thousand miles from its base ( and the Marshalls, which did not have a major naval base, were outside that range), and that a navy lost 10 percent of its fighting capability for every thousand miles it operated from its base. These were, however, battleship doctrines arising out of World war One, and Yamamoto’s attack would not be with battleships, but by carrier-based planes, armed with torpedoes and heavy bombs, and covered by fighter planes. His task force would be accompanied by oilers, so that refueling could take place at sea.

The effectiveness of a carrier-based torpedo-plane raid against warships at anchor in a harbor was tested in the naval wargames in April and May, 1940. As in most war games, there were disagreements in part with referee’s arbitrary decisions. But Rear Admiral Shigeru Fukudome, a senior naval aviation officer and Yamamoto’s chief of staff, concluded that the games had proved tat such an engagement would be a decisive victory, because the surface vessels would have no means of evading the torpedo planes. Admiral Yamamoto also concluded that amassed torpedo-plane attack, if it were a surprise, would be successful. When a similar attack was actually carried out in the British air raid on the Italian Fleet at Taranto on 12 November 1940, the results confirmed the evidence of the Japanese wargames, since twenty-one planes sank three Italian ships, with only two planes lost. Yamamoto ordered detailed studies of the Taranto raid to be made by Japanese naval attachés in London and Rome.

After receiving these analyses, Yamamoto ordered Fukudome to begin study of such an attack with planes carrying specially constructed shallow-running torpedoes, which cloud be launched at short range. Rear Admiral Takijiro Onishi and Commander Minoru Genda, one of Japans top airmen, were brought into the study. By January 1941, the finished report was available to Yamamoto, and he decided that , if war came, this would be the first blow struck by the Navy. After vigorous debate, Yamamoto was able to overcome the objections of Admiral Nagano, chief of naval staff.

Because most of the U.S. Pacific Fleet was constantly at anchor at Pearl harbor, plans for the surprise attack could begin immediately. A close surveillance of the U.S. Pacific Fleet at Pearl Harbor was begun by personnel attached to the Japanese consulate in Honolulu, and weekly summaries of the ships at anchor and at sea, and the schedules, were sent back to the naval intelligence in Tokyo. In September, Kagoshima Bay was chosen as the secret site for practicing a Pearl Harbor attack, and realistic training begins. Production of torpedoes with wooden fins, designed to run in Pearl harbors shallow waters, was undertaken.

By 3 November Yamamoto had overcome all opposition within the Navy; there would be a surprise attack on Pearl harbor, if the politicians and diplomats could not reach a peace settlement. Operation Order #1 was issued secretly to senior officers on 5 November; it read: “To the east, the American fleet will be destroyed. The American lines of operation and supply to the Far east will be severed. Enemy forces will be intercepted and annihilated. Victories will be exploited to smash the enemy’s will to fight.” Vice Admiral Nagumo, commander-in-chief of the First Air Fleet and overall commander of the Pearl harbor Strike Force, on his flagship, the heavy carrier Akagi, received specific and detailed orders on 11 November concerning the strike. Then on 25 November he received an order to sail the next day. Neither the original order nor the fragmentary order #9, issued to each unit of Nagumo’s strike force, even mentioned an attack on the oil storage tanks or machine shops at Pearl harbor–a fact which proved to be of no small importance.

Admiral Nagumo, who was regarded as a gruff and uncommunicative officer, was Japans top carrier commander. He did not believe in the Pearl Harbor raid, emphasizing to Yamamoto )with whom he was not on good personal terms with) that carriers were very vulnerable ships, although their planes could inflict damage, enemy planes could sink a carrier by scoring with only one or two well placed bombs or torpedoes. Nagumo would have preferred to cover the southern push, but, late in summer of 1941, he reluctantly accepted the idea of a Pearl Harbor strike.

On 22 November the task force began to assemble at Tankan Bay (also called Hitokappu) in the Kurile chain, north of Hokkaido. The raid was to hit Pearl Harbor at 0830 Sunday, 7 December. The Japanese had undertaken their vast preparations with the utmost secrecy; in order to hide the assembling of the Strike Force, warships in the Inland Sea had been generating false radio traffic, to lead American Intelligence to believe that the Japanese carriers were still in home waters. Actually, American intelligence, after having lost track of the carriers, deduced that they were on the move, but Pearl Harbor was never seriously considered as their destination.

Admiral Yamamoto issued the Strike Force’s sailing orders on 25 November: to sail on the following morning; to refuel at sea at a predetermined site on 3 December; and if they were not recalled, to launch an attack to hit Pearl Harbor as scheduled, and then to retire west in order to prevent a counterattack, returning to Japan.

Admiral Nagumo’s force sailed from Tankan Bay in extremely foggy weather, the carriers leaving at 0900 on 26 November. Their course took them through the deserted region of the North Pacific, south of the Great Northern Circle and north of the rhumb-line navigational routes between the Hawaiian Islands and Japan. The weather, however, was foul, with fog at times interspersed with winter gales–difficult weather for sailing in formation, but excellent weather for escaping detection. In the van, acting as a screen were the destroyers and light cruiser; next came the heavy cruisers, steaming abreast the six heavy carriers, which were in parallel columns of three each; last came the two battleships.The decision to carry out the attack came on 1 December, and the code message–“Niitaka yama nobore,” (“Climb Mount Niikata’)–was sent to Admiral Nagumo on 2 December. Now only premature detection could prevent the launching of the raid. On 3 December the wind abated, which allowed refueling to go ahead without difficulty. With smoother seas, the force, which had been sailing at an economical speed of 13 knots, increased its speed to 26 knots in order to reach the launch site on schedule. The fog, however, continued.

On Board the Akagi, Admiral Nagumo was worried about pre-strike detection, and about how much of the U.S. Pacific Fleet would be in the harbor at the time of the attack. Constant surveillance of Pearl harbor by Japanese consulate staff in Honolulu kept Tokyo and Nagumo’s strike force informed of U.S. ship dispositions. Nagumo hoped to find carriers anchored with the rest of the fleet, and when he sailed from Tankan Bay, he had been led to believe that there might be six carriers at Pearl harbor. Subsequently, he was informed that the heavy carrier Saratoga was at San Diego. Japanese intelligence had not yet discovered that the carrier Hornet and Yorktown were both stationed n the Atlantic.

By the evening of 6 December he knew the worst: according to the latest radio message from Tokyo, there were no carriers at Pearl harbor. For a commander making an air assault which was based upon the assumption that carriers were superior to battleships, this was discouraging news. It would not affect the outcome of the impending attack, but it di affect the attack’s strategic value to Japan. On the other hand, constant monitoring of American aerial patrols showed that their routine reconnaissance was directed to the south-west, leaving Nagumo’s launch point unobserved. As he neared Oahu, the commercial raid on stations were broadcasting only normal programming, with no hint of an alert. He was still undetected.

The weather worsened during the afternoon and early evening of 6 December, raising the concern that the planes could not be launched at the appointed time. At 2100, with the force still some 400 miles north of Oahu, Admiral Nagumo called all hands on deck throughout the fleet, and Admiral Yamamoto’s battle order was read: “ The rise or fall of the Empire depends upon this battle. Everyone will do his duty to the utmost“–a reiteration of Admirals Togo’s Nelsonian order before the battle of Tsushima Strait. In an emotional scene, the flag that Admiral Togo had raised on his flagship Mikasa, thirty-six years before, was raised on the Akagi. Then the force turned south at 26 knots. The launching point was to be 26 degrees North, 158 degrees West; Pearl harbor would be 275 miles away, due south.

The Strike force was by no means the only element in the Pearl Harbor attack plan. An advance force of twenty-seven submarines, most of them I-class, left the Yokosuka and Kure naval bases, beginning on 10 November. Eleven of the I-class carried small reconnaissance floatplanes. Five more submarines, I-16, I-18, I-20, I-22, and I-24 left on 18 November, each carrying a secret weapon: a midget two man submarine, designated Special Attack Unit, that could be launched from a mother ships near the attack area. Of the original twenty-seven, the I-26 went to the Aleutians and the I-10 to Samoa and the Fijis; the remaining twenty-five went to Kwajalein in the Marshall Islands, refueled there during 18-20 November, and then sailed to take up their war positions. They were to deploy around Oahu to furnish reconnaissance detail on the location, number, and kind of naval units in Pearl Harbor, to sink any ships escaping from the Strike Force’s attack, and to disrupt shipping between the United States mainland and the Hawaiian Islands. The five midget submarines were launched at 0100 on 7 December; a rendezvous for the recovery, never kept by the five, was designated off Lanai.

On 6 December, an I-class submarine scouted Lahanina Roads, an alternate anchorage used by the American fleet when it was not at Pearl Harbor. She signaled Admiral Nagumo via Tokyo that the U.S. fleet was not there. Nagumo knew, then, that most of the fleet was at anchor in the shallow waters of Pearl Harbor, at last report unprotected by any sort of torpedo nets. His unanswered question, however, were still with him: would any carriers join the main fleet during the night, and if not, where would they be? He now definitely knew that the heavy carriers Enterprise and Lexington were at sea.

Pearl Harbor Strike Force 7 December 1941

First Air Fleet: Heavy Carriers: Akagi (Flag), Kaga, Hiryu, Soryu, Shokagu, Zuikagu
Light Cruisers: Abukuma (Flag); Destroyers: Isokaze, Urakaze, Tenikaze, Hamakaze, Arare, Kasumi, Kagero, Shiranuhi, Akigumo

Support Force: Battleships: Hiei, Kirishima; Heavy Cruisers: Tone, Chikuma

Ship Lane Reconnaissance Units: Submarines: I-19, I-21, I-23

Midway Destruction Unit: Destroyers: Ushio, Sazanami

SOURCE: Battle History of the Imperial Japanese Navy (1941-1945); BY: Paul S. Dull

GOTO: World War Two: Day of Infamy, 7 December 1941


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