By William Price


On 20 May 1942 Admiral Yamamoto sent an operational order to his fleet commanders detailing the attack on Midway Island and the Aleutians. It gave a complete Order of Battle for both operations, it prescribed the bearings of approach for the attack, and the placement of naval forces at prescribed dates and times. For Midway there was a separate carrier attack force as well as an invasion force and screening submarines.

There are at least six publications that clearly reference this intercepted message.

They are:-

1. Incredible Victory by Walter Lord — This was perhaps the first published history (1967) to mention the Yamamoto message. Lord interviewed Rochefort, Holmes, and several key members of the HYPO cryptographic staff.

2. The Quiet Heroes of the Southwest Pacific Theater (NSA publication) 1996 by RADM Ralph Cook who observed the discovery of this message at FRUMEL.

3. The Codebreakers by David Kahn (1967) He describes the work in decoding and translating at HYPO to provide intelligence to ADM Nimitz. It is apparent that he interviewed key participants to obtain this detailed description.

4. Double Edged Secrets by Wm. Holmes (1979) who observed efforts to break this message at HYPO

5. The Role of COMINT in the Battle of Midway by Henry Schorreck (NSA Historian) (SRH-230, 1975) addresses this intercepted message of 20 May 1942.

6. The Unknown Hero of Midway A compilation I have made from the above along with evidence and conversations with RADM Ralph Cook who was an Ensign at FRUMEL and later commanded the Naval Security Group.


RADM Mac Showers was present at HYPO in 1942 as an Ensign. He participated in and contributed to the work on this intercept.

So both Mac and Ralph Cook recall the all out effort given this intercept of unusual detailed content. And it was all out.

These references are ample proof that this extremely important intercept existed. CDR Joseph Rochefort presented intelligence from this intercept to Admiral Nimitz. Officials in Washington tried to downplay the identification of AF as Midway, and as a consequence Rochefort had Midway send out the famous water shortage message. Despite warnings from Washington, Admiral Nimitz remembered that Washington had been wrong on Coral Sea, and Rochefort's HYPO had been correct. So Admiral Nimitz followed the intelligence from HYPO and dispatched three carriers to surprise the Japanese attackers.

A review of the books on Midway, especially those that focus on the Navy’s air attack that sunk four Japanese carriers, reveal that many are not aware of this critically important intercept. The Priceless Advantage from NSA, which devotes 88 pages to detail the Navy’s communications intelligence leading up to Midway, describes many intercepts of Japanese Navy messages related to the operation. But this very important message from Admiral Yamamoto is not mentioned because it was not in any of the reports used.

In trying to understand the rarity of this essential piece of intelligence, one can only assume that it was kept separate from other intercepts that were of lesser intelligence value. Perhaps the content of this message was so significant and of such an unusual find that it had to be given special handling and protection to conceal it from all but a select few.

As you may recall, in mid-1942 there was a leak about Japanese intercepts dealing with Midway. This leak appeared in Chicago and Washington newspapers, and this disclosure may have influenced the extra protection given to this very important intercept and comprehensive intelligence content. The public revelation of this intercept could have destroyed our communications intelligence capabilities for the remainder of the war. The Japanese would have been forced to change their code.

The following excerpts from published books describe the Yamamoto intercept. Before reviewing these sources, which focus on communications intelligence rather than details of the battle, a recent publication by an Australian has provided another aspect of the intercept.

In 2000, Michael Smith published The Emperor’s Codes: The Breaking of Japan’s Secret Ciphers. He discusses the Australian and British operations while at Hong Kong and Singapore, and later in Australia and India. In his chapter addressing the Battle of Midway, he indicates that the U. S. Navy’s intercept station at Wahiawa, Hawaii on May 20, 1942 intercepted a long message from Yamamoto to his fleet commanders. It was the final operation order for the Midway and Aleutians attacks. Wahiawa was a primary intercept station supporting HYPO . It is assumed that the intercept for FRUMEL was made at Moorabin, southwest of Melbourne. There were two or more courier runs daily from that station to the U. S. Navy’s cryptanalysts in Melbourne.

Smith’s research and interviews add another piece of information to the Yamamoto puzzle.


Intercept of the Yamamoto Message 20 May 1942
by Bill Price



I'd like to thanks Bill Price for allowing me to reproduce his above work on my "Australia @ War" web site.


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This page first produced 12 June 2008

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