One Japanese naval officer who did not witness the American fleet’s visit because he was on duty elsewhere was a young man who had been born Isoroku Takano. He changed his family name before long to Yamamoto, and he was to have most intimate dealings with the United States Navy a generation later. It was Yamamoto who, as commander of the Japanese fleet, devised and caused to be executed the famous blow at Pearl Harbor, and ever since then Americans have remembered him as one of the most dangerous enemies America ever had.

As a capable naval strategist, Yamamoto undeniably was dangerous. But he is remembered in America largely as an unbalanced braggart who gravely under-estimated American power: the author of the boast that he would force his way into Washington and dictate a peace in the White House.

Actually the Japanese admiral did not say that, and what sounded like a boast was simply an attempt to warn his fellow countrymen that they were biting off more than they could chew. This is brought out forcefully in an interesting new biography, Yamamoto: The Man Who Menaced America , by John Deane Potter, which offers a fascinating new glimpse at the great Pacific war.

Ten months before Pearl Harbor, says Mr. Potter, Yamamoto warned a friend that if war with America came it would be much harder than Japanese patriots supposed. It would not be enough, he said, for Japan to take Guam, the Philippines, Hawaii, even San Francisco; to win, “we would have to march into Washington and sign the treaty in the White House.” He added soberly: “I wonder if our politicians who speak so lightly of a Japanese-American war have confidence as to the outcome and are prepared to make the necessary sacrifices?”

Yamamoto himself did not have that confidence. On November 11, 1941, when he was just about to launch the blow at Pearl Harbor, he confided that he was in a strange position—“having to make a decision diametrically opposed to my own personal opinion, with no choice but to push full-speed in pursuance of that decision.” He realized that America simply had too much muscle. If Japan expected to win it would have to win very quickly, because if it came to a long war Japan would be hopelessly outclassed.

But his letter about signing the treaty in the White House became public; Japanese propagandists broadcast it as an expression of hope rather than as an appraisal of long odds, and naturally it was read with indignant interest in this country. It made Yamamoto one of the principal villains of the war as far as America was concerned, and that is how he is chiefly remembered to this day.

Yamamoto: The Man Who Menaced America, by John Deane Potter. The Viking Press. 332 pp. $6.50.

Yamamoto realized very well that Pearl Harbor did less than he