Henry Christian Clausen (1905 - 4 December 1994) was the author of the Clausen Report, an 800-page report on the Army Board’s Pearl Harbor Investigation. He traveled over 55,000 miles over seven months in 1945, and interviewed nearly a hundred personnel, Army, Navy, British and civilian, as a Special Investigator for the Secretary of War Henry L. Stimson carrying out an investigation ordered by Congress of the Secretary of War.
Clausen, a lawyer and a former Assistant U.S. Attorney from San Francisco, and a "civilian at heart" had joined up "for the duration" of the war, being discharged in August 1945. He was not a Reserve officer. He had been the Trial Judge Advocate for the Army at the (well publicized) court martial of Army inspectors for fraudulent inspections of aircraft engines at the Wright Aeronautical engine manufacturing facility in Lackland, Ohio.
He was a Republican like Stimson, who Clausen regarded as "a man of truly heroic stature". Clausen wrote about Congressman's Gearhart’s attack on him during the Congressional Hearing that "I was a Republican myself, and a fiscal conservative, too". He appeared before the Congressional Hearing, and was asked to show Congressman Murphy his Summary exhibit of Far Eastern documents, as Congressmen Ferguson and Gearhart who were in the "Kimmel camp" had held onto the two copies sent to the Committee to prevent other members seeing them.
He decided to write his book Pearl Harbor: Final Judgement in 1991 (published in 1992), in opposition to what he described as inaccurate conspiracy theories of the Pearl Harbor attack.
The Army Board Report and the Clausen Report 
Stimson got the Army Pearl Harbor Board report (actually two reports, with a second Top Secret section on codebreaking) on Pearl Harbor with its criticism of Marshall and Hull, but ‘fatally flawed’ from crucial but withheld evidence and perjured testimony. The Board had only learned of Magic's existence a week before it finished, and was initially not allowed access to the Navy Hewitt report until an appeal was made to Navy Secretary Forrestal. The three generals on the Board had all been relieved of commands by Marshall, hence were prejudiced against him. But they were available, so were put on the list of available officers for the Board by Marshall.
After discussing the Board report(s) with General Cramer (the Judge Advocate General) and with Major (later Lt. Col) Clausen (who had been Assistant Recorder to the Army Board), Stimson appointed Clausen as his Special Investigator to retake evidence and follow unexplored leads. Clausen and Colonel Hughes decided to ask:
- What had Pearl Harbor 'known' about Japanese intentions before the attack?
- What had Pearl Harbor 'done' with this information before the attack?
- What had Washington 'known' about Japanese intentions before the attack?
- What had Washington 'done' with this information before the attack?
Clausen had an authorising letter from Stimson informing witnesses he had the necessary clearances to require their cooperation, but he was often lied to until he produced copies of about 40 top secret ‘Magic’ decrypts, to prove he had the proper clearance. Previously they had been required to lie under oath to protect the secret of 'Magic'. He wore the decrypts in a self-destructing bomb pouch to satisfy security concerns.
The Fourteen-part Telegram and The War Warning 
Colonel Dusenbury, of the US Army SIS, testified that he received the fourteenth part (which said diplomatic relations would be broken) from the Navy (OP-20-G) about midnight (Washington time). No action was taken then; both Dusenbury and Commander Kramer, the translator, went home, and as much as nine vital hours (certainly three) were lost. The next morning Colonel Bratton arrived later on Sunday morning than he initially claimed during testimony and, Clausen concluded, invented a story about not being able to get in touch with Marshall which "nearly destroyed" Marshall.
Marshall got assurances that the final warning on December 7 would be received by everyone before 1 pm Washington time; he had to send Colonels Bratton and Bundy back to the message center twice to get this confirmation. But when Colonel French, in charge of the message center, learned that the War Department's radio system could not contact Pearl Harbor, he decided to send their message by RCA commercial radio – without telling Marshall of the delay.
The Pearl Harbor Commanders 
According to Clausen,
- Lt. Gen. W. C. Short didn’t want the command in Hawaii and failed to study what his task entailed. He failed to follow Washington’s orders to liase closely with the Navy, to conduct reconnaissance, or to get the radar equipment he had out of training mode (for several months), and he failed to alert his forces against attack as ordered.
- Adm. H. E. Kimmel withheld vital intelligence (e.g. the two messages about the destruction of codes and code machines by the Japanese, because he did not consider them as "being of vital importance") from his Army counterpart Short. Kimmel was inflexible in his convictions and expressions and would not liase with the Army about its state of readiness.
Clausen criticises others; Dusenbury, Fielder, Bicknell, Layton, Turner, Mayfield, Bratton, Rochefort, Gerow, and Kramer. And Roosevelt, for often vacillating, and for making a number of telephone calls after reading the Japanese message, but not one to Marshall. He does not think that a Winds Execute message was received, though there were several false leads given in testimony to the various investigators, and the FCC did intercept an IJN execute order with respect to England after Pearl Harbor.
Final Judgment 
Clausen saw the cause of being caught unprepared during the Pearl Harbor attack, as due both to having two separate commands at Pearl Harbor (Navy & Army), and to having two separate Intelligence organizations in Washington and elsewhere (Navy and Army), and so welcomed the combination of the Navy and Army efforts by Truman (eventually this came to be called NSA). MacArthur told him that he "had to barter like a rug merchant throughout the war to get the intelligence I have needed from the Navy." MacArthur also said that he got "ample and complete information" from the War Department prior to 7 December. MacArthur, like Clausen, was a Freemason (as was his subordinate Willoughby; and Truman). Clausen was asked to assist the local Freemasons in Manila, and was able to send them replacement Masonic item.
The arrangements in Washington prior to Pearl Harbor were inefficient and indicative of a peacetime mentality, e.g. the odd/even days arrangement for sharing cryptographic work between the Army and Navy. The Navy was sending intercepts by teletype, while the Army was using air mail before Dec 6. But the Navy only had Commander Kramer to distribute the material (with no relief for him) while the Army had both Colonels Bratton & Duensbury. Clausen says that the breach of Magic security in the White House was that Magic documents were found in the desk of Roosevelt’s military aide Maj. Gen Edwin M. 'Pa' Watson; not "in a wastebasket" as is often claimed.
Clausen disapproves of the policy amongst the cryptographers, and senior officers like Marshall, to lie under oath during the various investigations to keep Magic secret, but sympathizes with the quandary those officers faced in practice. And he decided that the most culpable officer, who had most failed in his duty, was Edwin Layton, Admiral Kimmel's Intelligence chief.
See also 
- Pearl Harbor: Final Judgment by Henry C. Clausen and Bruce Lee (1992, Crown Publishers, New York) ISBN 0-517-58644-4
- Book Cover, death year
- Text of Col. Clausen's report