ELINT, Information Operations Helped Japanese Forces Achieve Surprise at Pearl HarborOn December 7, 1941, air and naval forces of the Empire of Japan struck the US Navy base at Pearl Harbor, Hawaii, and surrounding Army and Navy facilities. Twenty-one ships of the Pacific Fleet were sunk or damaged in the attack, including two battleships sunk and six heavily damaged. Nearly 200 US aircraft were destroyed and over 150 damaged, most while still on the ground. Total US casualties amounted to 2,403 dead (68 of which were civilians killed by improperly fuzed anti-aircraft shells) and 1,178 wounded. Nearly 1,800 sailors perished on the battleship USS Arizona alone. Japanese losses amounted to 29 aircraft shot down and five midget submarines sunk or beached: 64 men in all.
The raid commenced when the Japanese cruisers Chikuma and Tone each launched a floatplane about 220 miles north of Oahu at 0530 local time to ascertain the exact anchorage of the US fleet. Twenty minutes later, the carriers of Japan's First Air Fleet, Akagi, Kaga, Hiru, Soryu, Zuikaku, and Shokaku turned into the wind to begin launching approximately 350 fighters and bombers in two waves. The aircraft included Nakajima Type 97 "Kate" level bombers, some armed with torpedoes and others with bombs; Aichi Type 99 "Val" dive bombers; and Mitsubishi Type 0 "Zero" fighters. Cmdr Mitsuo Fuchida, leading the first wave, used a Honolulu radio station broadcasting Hawaiian music to home in on the target. At 0735 the scout plane from Chikuma broke radio silence that had been maintained since the force left Japan twelve days earlier with a report that the US fleet was at its Ford Island anchorage. Fuchida sighted the ships at 0740 and saw that they were sleeping peacefully. As his attack wave divided into smaller units to deliver its ordnance, Fuchida radioed the code words signaling complete surprise had been achieved: "Tora! Tora! Tora!" ("Tiger! Tiger! Tiger!").
While credit for the success of the Japanese attack must go to the audacity and attention to detail of its planners -- particularly its chief architect, Admiral Isoroku Yamamoto, Commander in Chief of Japan's Combined Fleet -- the maintenance of strict radio silence for the entire outbound voyage played a crucial role in the results it achieved.
In the previous July, a Japanese carrier task force consisting of Soryu and Hiryu and their escorts accompanied the convoy of troop transports carrying Army forces to seize French Indochina. During its 2,000-mile voyage from Japan down the coast of China, the task force intercepted British radio reports from Hong Kong to London that pinpointed the location of the Japanese ships, and even identified specific types. The Japanese communications and intelligence officer understood that the British were plotting the fleet's movements using radio direction-finding equipment. This generated an official requirement that future task forces would maintain radio silence during an operation -- even to the extent of sealing transmitter keys -- and that efforts would be made by other units to send false messages to mislead whomever might be eavesdropping.
For the Japanese, the importance of radio silence surpassed even the benefits of aerial reconnaissance. The presence of six fleet carriers and several other vessels that carried floatplanes with the First Air Fleet would enable a system of air patrols to thoroughly cover huge swaths of ocean for ships and planes that might detect it. On the other hand, such a system of patrols increased the chances that a radio message would be sent in a hasty or unguarded moment, or if a pilot had an emergency. For the raid on Pearl Harbor, no air patrols were flown until the morning of the attack for just this reason.
Nevertheless, the interest in Japanese radio communications shown by US intelligence personnel both raised flags and caused strategists to second-guess themselves. The Japanese strike at Pearl Harbor was one of more than two dozen landings, raids, and related operations scheduled to coincide over a two-day period. As of December 1, the US was aware of a great "movement to the south" that presaged Japanese attacks on the Philippines, British possessions, and the Dutch East Indies. In fact, deployments southward of Japanese troop transports, supply freighters, destroyers, cruisers, and even battleships were indicated by radio traffic and this seemed to support preconceived notions among US planners that the inevitable blow would be struck in Southeast Asia, not the Central Pacific, let alone both.
There was some alarm at this point that no radio traffic had been identified from the Japanese fleet carriers for many days. Furthermore, the Japanese had just changed their radio call signs for the second time in a six-month period, which was unprecedented. Even more disturbing to some was the overall precipitous drop in the volume of Japanese radio traffic. However, US intelligence officers were "confident" that the carriers were in the home waters of Japan and not "rounding Diamond Head" as Admiral Husband E. Kimmel, Commander in Chief of the US Fleet, half-jokingly speculated. Such confidence on the part of seasoned intelligence officers was born of disbelief that the Japanese could mount a carrier attack on Pearl Harbor. If the Japanese carriers were not heading south, then they must be in their home waters, or so went conventional wisdom.
Upon recovering his aircraft Vice Admiral Chuichi Nagumo again clamped strict radio silence over the First Air Fleet. The US carriers Enterprise and Lexington were at sea somewhere nearby, and the last thing he wanted was an unexpected encounter. Nagumo did order air patrols to cover his withdrawal from Hawaiian waters, prepared to strike the enemy if he encountered him. Fortunately for the US flattops, perhaps, the First Air Fleet retired without such an encounter.
Raid Spurs EW Developments
The first moves to form an organization in the US devoted solely to the development of radio countermeasures came from the Navy on December 11, 1941, just four days after the Japanese attack on Pearl Harbor. On that day, Admiral Julius Furer, one of the coordinators of naval research and development, convened a preliminary meeting to discuss setting up such an organization. Following this, a letter was sent to the National Defense Research Committee (NDRC), requesting that it consider forming an organization to develop countermeasures equipment. The recommendation was accepted.
--From The History of US Electronic Warfare, Volume 1 by Alfred Price (AOC, 1984), pg. 19
For more information on the Pearl Harbor raid, consider the following books and websites:
The History of US Electronic Warfare, Volume 1 by Alfred Price (AOC, 1984)
At Dawn We Slept, The Untold Story of Pearl Harbor by Gordon W. Prange (Penguin Books, 1982)
"Modern History Sourcebook: Pearl Harbor Attack Documents, 1941"
"Pearl Harbor Operations: General Outline of Orders and Plans"
See the Nagasaki post for information on the raid that ended the Pacific War.
UPDATE: Roundups of posts on the Pearl Harbor attack can be found at the following sites:
La Shawn Barber's Corner
Winds of Change