Preparation and Sortie for the Pearl Harbor Attack

The Hawaii operation was conceived by Combined Fleet commander Adm. Yamamoto Isoroku. In January 1941 he set out in a letter to Navy Minister Oikawa Koshiro the idea of opening the war with an air attack on Hawaii, and later that month asked Rear Adm. Onishi Takijiro, chief of staff of the Eleventh Air Fleet, to study it; Cdr. Genda Minoru, air staff officer of the First Carrier Division, produced a draft around February, which Onishi then revised. The First Air Fleet, concentrating the carriers under one command, was formed on 10 April 1941. The Naval General Staff at first opposed the plan as too risky; after resistance that continued beyond the war games held at the Naval War College in September, and after Yamamoto threatened to resign, Chief of the Naval General Staff Nagano Osami approved the use of all six carriers on 19 October 1941.

Carrier air groups trained for shallow-water torpedo attack, dive bombing and level bombing at bases around Kagoshima (Kinko) Bay and elsewhere in Kyushu, including Kanoya, Izumi and Kasanohara, with final exercises held in Saiki Bay. Because Pearl Harbor is only about 12 metres deep, the Type 91 aerial torpedo was fitted with wooden stabilising fins to keep it from diving too deep on entry; the modified torpedoes were delivered only in mid-November. The level bombers carried Type 99 No. 80 Mk 5 armour-piercing bombs converted from battleship shells.

The First Air Fleet under Vice Adm. Nagumo Chuichi, built around the carriers Akagi, Kaga, Soryu, Hiryu, Shokaku and Zuikaku and accompanied by the battleships Hiei and Kirishima, the heavy cruisers Tone and Chikuma, the light cruiser Abukuma, nine destroyers and a group of tankers, left Saiki Bay and other Inland Sea anchorages in secrecy from about 18 November, took a northern route to avoid merchant shipping lanes, and had assembled at Hitokappu Bay on Etorofu in the Kuriles by 22 November. It sailed for Hawaii on the morning of 26 November 1941.

Yamamoto remained aboard the Combined Fleet flagship Nagato at the Hashirajima anchorage in Hiroshima Bay. The Imperial Conference of 5 November approved the outline of national policy and that of 1 December formally decided on war. At 17:30 on 2 December the order fixing the opening of hostilities for 8 December (Japan time), the coded signal known as Niitakayama nobore 1208, was transmitted to the fleet; according to Japanese Wikipedia it was sent from the Navy's Funabashi transmitting station. The attack on Pearl Harbor took place on the morning of 7 December Hawaii time (8 December in Japan), and the 'Tora Tora Tora' signal sent by strike leader Fuchida Mitsuo was received directly aboard Nagato. This record concerns the home-island sites connected with the planning, training, command and communications for the operation rather than the attack itself.