DOCID_3177591_SEALED_OK.PDF

Doc ID: 3177591
Doc Ref ID: A411685
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What Every Cryptologist Should Know 
about Pearl Habor (U}-----------------------------------------------------------------TOM .JOHNSON 
55 
(U) Further analyses of the events surrounding 
the "day that will live in infamy." 
Approved for release in FOIA Case 114591 as released in MDR Case 52993 on July 11, 2007    

Doc ID: 3177591                                      Doc Ref ID: A411685
What Every Cryptologist Should 
Know about Pearl Harbor 
TOM JOHNSON 
UNCLASSIFIED 
The surprise Japanese attack on Pearl Harbor in 1941 was an event of surpassing 
importance in American history. But beyond that, it was the most important event of 
American cryptologic history. As cryptologists we should study Pearl Harbor for its 
impact on our profession. This impact is felt in two ways. 
a. 
It has influenced how the American public views our profession. This has been 
influenced, in turn, by the winds of political ch…

Doc ID: 3177591                                      Doc Ref ID: A411685
UNCLASSIFIED 
CRYPTOLOGIC QUARTERLY 
That was on 23 January 1942, only a month after Knox had returned from Hawaii. 
The administration was clearly proceeding with a good deal of haste to identify the 
culprits. On 28 February Knox and Stimson issued statements accepting the retirements 
of Kimmel and Short. A statement of charges was being prepared concerning dereliction 
of duty, which would later be adjudicated in a courts martial. The trial would proceed, 
however, "only at such a time as the public interest and safet…

Doc ID: 3177591                                      Doc Ref ID: A411685
WHAT EVERY CRYPTOLOGIST SHOULD KNOW 
UNCLASSIFIED 
met long ago. Now it just so happened that controversy over the Army and Navy boards 
occurred in the middle of the 1944 Presidential election. The Republicans were having 
difficulty finding an issue that would convince the public to evict a President in the 
middle of a world war. Surprise at Pearl Harbor was one of their few useful weapons. 
Republican congressmen began raising the cry of cover-up. Hugh Scott, a senator from 
Pennsylvania, claimed to know that the Aust…

Doc ID: 3177591                                      Doc Ref ID: A411685
UNCLASSIFIED 
CRYPTOLOGIC QUARTERLY 
The testimony of General Marshall and Admiral Stark would indicate that the Chief Executive took 
the ominous news so calmly that he made no effort to consult with them. Did he deliberately seek the 
Pearl Harbor attack in order to get America into the war? ... This problem grows more complicated as 
we watch the approach of zero hour. At 9:00 A.M. on 7 December, Lieutenant Commander Kramer 
delivered to Admiral Stark the final installment of the Japanese instruction to Nomura .... But…

Doc ID: 3177591                                      Doc Ref ID: A411685
WHAT EVERY CRYPTOLOGIST SHOULD KNOW 
UNCLASSIFIED 
The far right began losing its influence in the early days of the Eisenhower 
administration, and McCarthy died in 1957 a thoroughly discredited man. At the same 
time the academic debate over revisionism faded after the publication of Barnes's book. 
The argument was temporarily revived in 1955 by the publication of Admiral Kimmel's 
memoirs (Admiral Kimmel's Story), which took the administration to task for 
withholding information from the commanders at Pearl Harbor. K…

Doc ID: 3177591                                      Doc Ref ID: A411685
UNCLASSIFIED 
CRYPI'OLOGIC QUARTERLY 
called by the American cryptologists JN-25, and were privy to Japanese intentions, even 
though the American Navy had not yet broken it. (He also noted with interest that the 
U.S. had given the British a Purple analog machine, used to decipher Magic traffic, and 
speculated that they might have had more Magic decrypts than we did.) He went on to 
hypothesize that Churchill may have either passed a warning to Roosevelt on 26 
November, in which case the Americans would be culpable for…

Doc ID: 3177591                                      Doc Ref ID: A411685
WHAT EVERY CRYPTOLOGIST SHOULD KNOW 
UNCLASSIFIED 
According to Toland, other Sigint-based warnings came from the Dutch, who had 
broken Japanese consular codes and had information about Japanese attacks on Hawaii, 
Philippines, Malaya, and Thailand. (This was entirely possible since the consular codes 
were known to be vulnerable, and some of the messages did carry information of this 
type.) Still another warning came from the British, who on 6 December warned the 
American observer in Cairo, Colonel Bonner Fellers, of …