Attack on Pearl Harbor: Encyclopedia II - Attack on Pearl Harbor - Japanese preparations

Attack on Pearl Harbor - Japanese preparations

The Japanese had seized Manchuria in 1931, and had been fighting the Second Sino-Japanese War with China since 1937. During 1941 the long-standing tensions between the Japanese Empire and the United States resulting from these military adventures were rising. The United States and the United Kingdom reacted to Japanese military actions in China by imposing a scrap metal boycott followed by an oil boycott, a freeze of assets and the closing of the Panama Canal to Japanese shipping. Diplomatic negotiations climaxed with the Hull note of November 26, 1941, which Prime Minister Hideki Tojo described to his cabinet as an ultimatum. The oil boycott beginning in the summer was especially threatening to Japan (and the Navy), which lacked oil resources of its own. Japanese leaders saw only two choices: give in to the demands of the USA and the UK and back out of China, or escalate the conflict to try to acquire control of oil and other resources -- primarily in Southeast Asia. By the time of the Hull note, they had settled on the second course.

The Japanese had been impressed with Admiral Andrew Cunningham's Operation Judgement (the Battle of Taranto), where 20 elderly biplanes (Fairey Swordfish) launched from a carrier force way in advance of the main British base at Alexandria disabled half the Italian battle fleet and forced the withdrawal of the Italian fleet to behind Naples. Yamamoto dispatched a naval delegation to Italy, which concluded a larger and better supported version of Cunningham's brilliant maneuver could force the U.S. fleet back to California, giving time to achieve the "Greater East Asia Co-Prosperity Sphere"—shorthand for control of the oil reserves of the Dutch East Indies, with a defensible buffer around them. Most importantly, the delegation returned to Japan with the secret of the shallow running torpedo which Cunningham's "boffins" had devised.

Additionally, some Japanese strategists may have been influenced by the actions of U.S. Admiral Harry Yarnell in the 1932 joint Army-Navy exercises, which presumed an invasion of Hawaii by hostile forces. Yarnell, in the role of the commander of the attacking fleet, sailed his aircraft carriers northwest of Oahu into rough weather, and launched attack planes on the morning of Sunday, 7 February 1932. "Judges" assigned to gauge the effectiveness of the attack noted that Yarnell's aircraft were able to inflict serious damage on the defenders, who were unable to locate his fleet 24 hours after the attack. Conventional Navy doctrine of the time believed that any attacking force would be set upon and destroyed by the battleship fleet stationed at Pearl Harbor, and dismissed Yarnell's strategy as impractical in the real world.

The intent of the attack on Pearl Harbor was to neutralize American naval power in the Pacific, if only temporarily, as part of a theater-wide, near-simultaneous coordinated attack against several different countries. Admiral Isoroku Yamamoto himself expected that even a successful attack would gain only a year or so of freedom of action. Preliminary planning for a Pearl Harbor attack in support of military advance elsewhere began in January 1941, and training for the mission was under way by mid-year when the project was finally judged worthwhile after some Imperial Navy factional infighting. The planned attack depended on torpedoes, but the weapons of the time required deep water to function if air launched. Over the summer of 1941, Japan secretly created and tested torpedo modifications that could be expected to work properly after air drop in shallow water. The effort resulted in the Type 95 torpedo which inflicted most of the damage to U.S. ships during the attack. Japanese weapons technicians also produced special armor-piercing bombs by fitting fins on 14 and 15 inch (356 and 381 mm) naval gun shells. These were able to penetrate the armored decks of battleships and cruisers when dropped from 10,000 feet (3,000 m).

On November 26, 1941, a fleet including six aircraft carriers commanded by Japanese Vice Admiral Chuichi Nagumo left Hitokappu Bay in the Kuril Islands under orders for strict radio silence bound for Hawaii. The aircraft carriers involved in the attack were: Akagi, Hiryu, Kaga, Shokaku, Soryu, and Zuikaku. Two fast battleships, 2 heavy cruisers, 1 light cruiser, 9 destroyers, and 3 fleet submarines provided escort for the task force. The carriers had a total of 423 planes, including Mitsubishi Type 0 "Zero" fighters, Nakajima Type 97 "Kate" torpedo bombers, and Aichi Type 99 "Val" dive bombers. The Japanese task force and its air group were larger than any previous aerial strike force. Accompanying the fleet were 8 tankers for underway refueling. In addition, the Advanced Expeditionary Force included 20 fleet submarines and 5 2-man Ko-hyoteki-class midget submarines; they were to gather intelligence and sink any U.S. vessels that might try to flee Pearl Harbor during the air attack.

Adapted from the Wikipedia article "Japanese preparations", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki