Battle of Midway, 4-7 June 1942 --
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The Battle of Midway, fought over and near the tiny U.S. mid-Pacific base at Midway atoll, represents the strategic high water mark of Japan's Pacific Ocean war. Prior to this action, Japan possessed general naval superiority over the United States and could usually choose where and when to attack. After Midway, the two opposing fleets were essentially equals, and the United States soon took the offensive.

Japanese Combined Fleet commander Admiral Isoroku Yamamoto moved on Midway in an effort to draw out and destroy the U.S. Pacific Fleet's aircraft carrier striking forces, which had embarassed the Japanese Navy in the mid-April Doolittle Raid on Japan's home islands and at the Battle of Coral Sea in early May. He planned to quickly knock down Midway's defenses, follow up with an invasion of the atoll's two small islands and establish a Japanese air base there. He expected the U.S. carriers to come out and fight, but to arrive too late to save Midway and in insufficient strength to avoid defeat by his own well-tested carrier air power.

Yamamoto's intended surprise was thwarted by superior American communications intelligence, which deduced his scheme well before battle was joined. This allowed Admiral Chester W. Nimitz, the U.S. Pacific Fleet commander, to establish an ambush by having his carriers ready and waiting for the Japanese. On 4 June 1942, in the second of the Pacific War's great carrier battles, the trap was sprung. The perserverance, sacrifice and skill of U.S. Navy aviators, plus a great deal of good luck on the American side, cost Japan four irreplaceable fleet carriers, while only one of the three U.S. carriers present was lost. The base at Midway, though damaged by Japanese air attack, remained operational and later became a vital component in the American trans-Pacific offensive.

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Why There Was a Battle for Midway

By Wm. Price

PRESENTED AT THE U.S. NAVY’S MIDWAY COMMEMORATION

June 4, 2009

Navy Memorial

Pennsylvania Avenue , Washington, DC

Military victories are often attributed to brilliance of the commander, but on close inspection, it will be found that victories can be attributed to the intelligence that was available; so a combination of G2 and IQ are essential to victories

This was true at Midway — where we had the best tactical intelligence during WWII — a 12-part operational order fromADM Yamamoto

Today I wish to share with you WHY there was a battle for Midway — a specific reason WHY — and not one of generalities. But first let’s examine the background.

The Navy’s cryptographic effort was started in WWI by Agnes Driscoll who trained all the Navy’s cryptographers. Many officers were also trained at the American Embassy in Tokyo as Japanese linguists. Intercepting messages and breaking codes was known as radio or communications intelligence — COMINT. NEGAT, was the headquarters in Washington. It was subordinate to Naval Communications and its organizational designator was OP-20-G. Corregidor or CAST was our Navy’s largest code breaking unit in the field. The other, HYPO, was at Pearl Harbor and advised ADM Nimitz directly

They were assisted by the the British, Australians and the Dutch. By December 1940 some 1,300 JN-25 code meanings had been recovered. Ten different codes were used by the Japanese Navy, and by the end of the war they had used 184 different code systems

The operational code for the Japanese Navy, JN-25, was composed of 5 numbers in groups representing words and phrase. It was introduced in June 1939, and the Japanese called it D IPPAN RAI. When new code books were issued, we identified them with an alphabetic suffix, e.g. JN-25A. The code book consisted of about 30,000 text entries.

In use, text of message was converted to 5-digit code groups, and to further hide the contents, these 5-digit code groups were added to a cipher of random 5-digit numbers. The sum was then transmitted as a message. Additionally there were 2 digit geographic codes. Midway was AF, and there was a special Date/Time code.

The cipher tablets were changed and reissued more frequently than the code books. We identified the cipher versions with a number suffix JN-25A1, following the Japanese D IPPAN RAI A1

In 1940 Corregidor was the first to break into JN-25 By March 1942 Corregidor had recovered 10,200 code groups. But in that month the analysts at Corregidor began evacuation by submarine to Melbourne, Australia. Three submarine trips were made and the last group left on 18 April as Bataan fell to the Japanese. The radio intelligence effort was reestablished im Melbourne, Australia as FRUMEL or Fleet Radio Unit Melbourne.

JN-25B had been in use since Dec. 1940 but on May 28 1942 JN-25C9 was introduced. Before the change, on May 20 we got our best intercept of the war — a 12-part message from ADM Yamamoto

One of these intercept stations supporting Melbourne was at Moorabin, just outside the city. Several motorcycle trips were made daily to bring intercepted messages to the apartment building where our cryptanalysts evacuated from Corregidor worked. At 11:30 on the night of May 20, 1942 Yeoman Bill Tremblay had processed all the intercepted messages that were complete. His job was to subtract cipher from the message to reveal the underlying code. These coded messages were then given to the Translating Group that would decode and translate these messages into English.

Bill was at the end of his 12-hour shift; so rather than preparing to leave, he reached into a box of “Crap Traffic”, messages that were garbled and incomplete due to atmospheric disturbances that hindered copying.

Bill quickly scanned these messages to begin processing one of importance. The subject line, precedence for delivery, security classification, and length were indications of potential importance. Bill selected a 12-part message dated May 20 that had the subject line “Operational Order 14”. He quickly started subtracting cipher groups from this message. To keep from getting bored with such a repetitive job, Bill had memorized some of the important code groups. Soon he discovered the code for ATTACK and the geographic code AF which they had already identified as Midway Island. He excitedly grabbed the Chief Petty Officer who then awakened the Duty Officer, Lieutenant Commander Gil Richardson, who was chief of the Translating Group. Recognizing the significance of this intercept as a directive from Admiral Yamamoto’s headquarters, the remaining parts of this garbled message were pulled together. This message contained the complete plan for the attack and capture of Midway and the Aleutian Islands.

HYPO was quickly notified through COPEK, the secure communication facility. HYPO was also understaffed and working 12-hour shifts; so they began to search through their intercepts. Since this message was a garble it had also been placed aside as secondary importance for processing. However HYPO’s intercept was garbled in different places and contained portions that FRUMEL didn’t have.

Their best cryptanalysts/linguists were put to work while FRUMEL continued to forward their results as they too decoded this important message. In 2009, two officers involved remember the effort that was devoted to this important intercept, Rear Admiral Ralph Cook in Honolulu, and Rear Admiral Mac Showers in Arlington, Virginia. Ralph was at FRUMEL and Mac was at HYPO,. and both were Ensigns in 1942. They clearly recall this event and the concentration of effort to decode and translate this important intercept.

Over three days of around the clock effort was devoted to this 12-part message. But being garbled made the work more difficult in properly aligning the cipher tablet with the message groups. Synchronization had to to be exact. Success was slowly evolving as the contents appeared. An important part of the message was the planned date of attack. This was in a different or super code. It had only appeared in two other intercepts; so there had not been sufficient depth for analysis to break this unique code. Both FRUMEL and HYPO concentrated on this DATE/TIME code, and finally both broke it. It turned out to be a matrix representation.

Now the Fleet Radio Units had everything from the Yamamoto intercept of May 20. The date of attack was June 4. The message, a directive to Japanese fleet admirals, was based on results of wargaming the Midway operation at Japanese Naval Headquarters. This directive specified:

• The complete order of battle for all Midway and Aleutian forces.
• Direction and bearing for the carrier attack force to approach Midway.
• The route, location and time to launch the attack on Midway.
• The composition, approach and time for the invasion force from Saipan to land.

This intelligence was taken by HYPO’s commander, Joseph Rochefort to brief ADM Nimitz on May 23. Nimitz now knew everything the Japanese knew and more. He had the intelligence essential to defend Midway.

However there were only three aircraft carriers at his disposal: the Enterprise, Hornet and Yorktown. The carrier Lexington had been sunk and the Yorktown had been badly damaged in May at the Battle of Coral Sea. A month of round the clock repair work was required to make the Yorktown battle worthy. Only three days could be allowed.

At Nimitz’s direction, these three carriers were dispatched to Point Luck northeast of Midway. Here they would wait and ambush the four Japanese carriers. At 0515 on 4 June 1942, LT Howard Ady, flying a PBY-5 patrol plane, spotted the Japanese carriers and verified the radio intelligence. This set the wheels in motion. Following attacks by several squadrons from Midway, beginning at 1020 our carrier based dive and torpedo bombers quickly struck the Akagi, Kaga, and Soryu setting them afire to sink within 5 minutes. Later that afternoon, the Hiryu was located and sunk.

Though outnumbered, ADM Nimitz was given a decided advantage with his Navy’s radio intelligence, and his carrier based pilots had the leverage to avenge Pearl Harbor. Although less experienced than the Japanese pilots, they had exceptional skill and the determination to win and avenge Pearl Harbor. These brave and daring pilots and their gunners successfully halted the Japanese advance in the Pacific. This victory allowed the War Department in Washington to focus on Europe and accelerate the invasion at Normandy by two years.

Midway was the greatest Naval victory in history that defeated the largest armada that Japan had ever launched.