Isoroku Yamamoto's sleeping giant quote

Isoroku Yamamoto is credited with saying, after the attack on Pearl Harbor, "I fear all we have done is to awaken a sleeping giant and fill him with a terrible resolve." The earliest citation for that theatrical comment, however, is the (reasonably accurate) movie, Tora! Tora! Tora! (1970). That quotation was accepted and repeated verbatim in the movie Pearl Harbor (2001). However, no one has been able to verify that Yamamoto ever actually said (or wrote) those words.

Randall Wallace, the screenwriter of Pearl Harbor, readily admitted that he copied the line from Tora! Tora! Tora!. (Pearl Harbor is not troubled by accuracy; among other examples of dramatic license, it shows Yamamoto saying those words while standing on a carrier in the attacking force despite the fact that he was on board his flagship anchored at a naval base in Japan throughout the attack.) The book Tora! Tora! Tora![?], written by the highly respected Gordon Prange, does not contain the line.

The director of the movie Tora! Tora! Tora!, Richard Fleischer, stated that while Yamamoto may never have said those words, the film's producer, Elmo Williams, had found the line written in Yamamoto's diary. Yamamoto, however, never kept a diary. Williams, in turn, has stated that Larry Forrester, the screenwriter, found a 1943 letter from Yamamoto to the Admiralty in Tokyo containing the quote. However, Forrester cannot produce the letter, nor can anyone else, American or Japanese, recall or find it.

Yamamoto certainly believed that Japan could not win a protracted war with the United States. The line serves very well as a dramatic ending to the attack. It does not seem, alas, to have been real.