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Code Breaking and the
Battle of Midway Island

The Significance of
the Battle of Midway

In the three months following the Pearl Harbor attack the Japanese invasion fleet rampaged over southeastern Asia and the islands of the western Pacific.

Japanese Conquests
Major Territories
Indo-ChinaSep. 1940
PhilippinesDec. 1941
IndonesiaJan. 1942
MalayaJan. 1942
BurmaMay. 1942
BorneoFeb. 1942
New Guinea
Mar. 1942
Smaller Islands
GuamDec. 1941
WakeDec. 1941
CelebesFeb. 1942
SarawakFeb. 1942
SingaporeFeb. 1942
CarolinesAug. 1943
GilbertsAug. 1943
MarshallsAug. 1943
MarianasAug. 1943
Aug. 1943

In addition there were major attacks on Ceylon (now Sri Lanka) and Darwin, Australia. The Island of Taiwan (Formosa) was under Japanese control and had been since 1895.

In the months following Pearl Harbor the Japanese invasion forces appeared to be invincible. The significance of the Battle of Midway was that a major Japanese attack was decisively defeated effectively ending the expansion of Japanese control. Thereafter the war consisted largely of a slow, costly territory-by-territory defeat of the Japanese occupation forces.

Decoding by the American Navy

In the 1920's there was no effort by the U.S. Navy at decoding other country's messages. In the late 1930's decoding department was established but for years it consisted of one person. When Commander Joseph J. Rochefort, the person principally responsible for cracking the Japanese naval operations code, joined the decoding department he was only the second staff member. Then his boss left on another assignment and again it was a one-person department.

The Japanese coding system was simple and appeared to be unbreakable. The characters of the Japanese writing system were assigned numbers and then random numbers from a book of random numbers were added to the character numbers. The first random number was added to the first word of the message; the second random number of the page was added to the second character number and so on. Hidden in the coded message was page number of the page of random numbers used in the coding. From time to time the book of random number would be changed. It seemed impossible to break but the decoding department of the U.S. navy did manage to break it.

By 1941 the decoding department had grown and had the major success of having broken the diplomatic code of the Japanese. In early December of 1941 the department was able to decode messages from the Japanese in Tokyo to the Japanese embassy in Washington, D.C. telling them to close the embassy and destroy code books. It was easily deduced that Japan was going to go to war with the U.S. The nature of how the war would start was not known. In Europe there had been declarations of war and no actions for several months.

The concentration of the decoding effort on the diplomatic code resulted in a neglect of operations code of the Japanese navy. Decoding that code would provide information on the where and when of Japanese naval operations.

The Japanese Attack on Pearl Harbor

The U.S. and its allies tried to curb Japan's military actions in China by cutting off its supples of crucial materials, particularly those steel and petroleum. Japan treated those actions as acts of war.

The Japanese government and military decided that assured supplies of those resources could be obtained by taking control of the territories of southeast Asia, particularly the Dutch East Indies. The only country which could thwart this conquest was the United States. Thus there would have to be a lightning strike that would effectively destroy the U.S. navy in the Pacific. Such a surprise attack had given Japan victory over the Russian Empire.

The Japanese admiral Isoroku Yamamato was given the task of planning the strike on Pearl Harbor. Yamamato was not in favor of Japan making war on the U.S. He had been educated in the U.S. and knew the awesome size of America's industrial might in comparison to that of Japan. He knew that in the long run the U.S. would defeat Japan. He believed that Japan's only hope was to strike some devastating blow and then negotiate a truce. Yamamato may have known the industrial might of the U.S., but he was sorely mistaken about American culture to think that the U.S. would settle for anything less than the unconditional surrender of Japan.

Yamamato put together a devastating attack force based upon six aircraft carriers supplemented by 2 battleships, 3 cruisers and 9 destroyers. The were six aircraft carriers carried 414 planes, 353 of which made attacks. There were bombers and torpedo planes involved as well fighter planes.

This force sunk or damaged 8 battleships and destroyed 188 planes and damaged 159 others. The human losses for America were 2403 killed and 1178 injured.

In spite of all the pain and devastating involved in the Japanese attack on Pearl Harbor, militarily it was failure because it did not destroy America's aircraft carriers. Of the 8 battleships sunk or damaged 6 were brought back into service in the war. The evidence for this assertion is the decisive defeat suffered by Japan seven months later in the Battle of Midway Island that showed that Japan's ultimate defeat was inevitable. Nevertheless the Japanese went home from Pearl Harbor indulging in the hubris that is the fatal flaw of Japanese culture.

The Doolittle Bombing Raid on Japan

In the months following Pearl Harbor American psyches ached for some gesture response. The military settled on sending long range bombers to bomb Tokyo and other major cities of Japan. There were no available air fields within range so the planners decided upon launching B25 bombers from aircraft carriers. An aircraft carrier just barely had room enough for such heavy planes to take off. There would be no chance of them landing on an aircraft carrier so they would have to fly to a friendly part of China. The pilots practiced short-field takeoffs in Florida in preparation.

The project was under the command of Lieutenant Colonel James Doolittle. Eighteen bombers were launched successfully from an aircraft carrier under the command of "Bull" Halsey. The bombers made it to Tokyo and the other cities and dropped their bombs. Some made it to China and others came down in Japanese territory and the crews were captured.

The raid was probably only important in terms of morale. The Japanese thought it was essential to prevent any more such raids. Such raids could endanger the Emperor. The Japanese military incorrectly deduced that the raid had been launched from Midway Island and therefore Midway Island had to be captured.

The Japanese Attack Force
Sent to Midway Island

Admiral Yamamato had responsibility for planning the attack on Midway Island and as was his forte it was massive coordination of naval and aircraft power. It involved two hundred ships and 250 aircraft organized into five separate forces. The naval force included eight aircraft carriers, eleven battleships and 23 cruisers. Not all of these were devoted to the attack on Midway. There was to be a diversionary attack on the Aleutian Islands of Alaska.

The strike force for Midway consisted of four aircraft carriers and two battleships. An Occupation Force consisted of twelve troopships for landing five thousand soldiers on the island. Twenty submarines were to be stationed between Midway and Hawaii to prevent forces from Hawaii coming to the aid of Midway.

The American Naval Defense Force
Sent to Midway Island

From the decoded operational messages, the Americans knew an attack was being planned but they did not know the target. Many in the decoding operation correctly surmised that Midway Island would be the target. However there were some in authority that feared the target might be Hawaii or the West Coast. They did not want defense forces assembled at Midway if Hawaii was going to be the target.

The situation was resolved sending a message to Midway by secure undersea cable telling them to send an unencoded message by radio to Hawaii announcing that their water desalinization plant had failed and that they had only a two week supply of fresh water. Hawaii sent back a message that the replacement plant was on its way. From the flurry of Japanese messages that resulted from this ploy it was obvious that Midway was to be the target.

The Task Force assembled by Admiral Nimitz for the defense of Midway Island consisted of three aircraft carriers: Hornet, Enterprise and Yorktown. The Yorktown had been badly damaged in the Battle of the Coral Sea but fifteen hundred men working around the clock had her repaired in three days. The American task force arrived in the vicinity of Midway before the Japanese one did.

The Course of the Battle

The Decoded messages revealed the Japanese intended to launch their attack from an area to the northwest of Midway. That gave the Americans the advantage of knowing where to search for their enemies. Unfortunately that was not enough of advantage to offset superior number and superior quality of the Japanese Zero fighter planes. When the 26 outmoded fighter planes from Midway Island confronted an attack swarm of 108 Japanese fighters and bombers 15 of American fighters were shot out of the sky and of the 11 that landed back at their base at Midway 9 were destroyed on the ground. But the anti-aircraft guns on Midway put 67 of the 108 Japanese attack planes out of action.

The American carriers had more modern aircraft than those based at Midway but they too were heavily damaged by the anti-aircraft guns of the Japanese fleet and the 50 Japanese Zeroes protecting the fleet. Of the 41 planes launched from the American carriers only four made back to their carrier. However just when the Japanese carriers were dealing with the landing and refueling of their planes a fleet of 32 Dauntless bombers from the American carrier Enterprise and 17 from the Yorktown came into the area unnoticed at a higher altitude. The bombers from the Enterprise immediately went into dives to hit the Japanese carriers Kagi and Akagi. There were multiple direct hits from the bombers and additional damaged from the explosions of the Japanese planes on the decks of the carriers.

The American bombers from the carrier Yorktown also scored direct hits on the Japanese carrier Soryu. A fourth Japanese carrier Hiryu escaped notice and launched planes that hit the Yorktown and put it out of commission by badly damaging its engines.

All of the 24 planes left on the Enterprise were launched against the Hiryu. They scored four direct hits that set the Hiryu on fire which destroyed her.

Thus in the course of one day Japan lost four aircraft carriers. In addition she lost more than 300 aircraft and 3000 men. The Japanese attack force still had battleships left but without the protection of aircraft from the carriers they would be vulnerable targets. Yamamoto decided to accept the failure of his attack on Midway and withdrew his fleet to the west. Yamamoto did not know it but he had signed his own death warrant for his role in the planning of the attack on Pearl Harbor. Through the decoded Japanese operational messages the Americans spotted evidence of Yamamoto traveling by plane. They sent fighter planes to intercept Yamamoto's plane and shoot it down.

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