The admiral’s grandson Sen. John McCain tells that story to begin his moving memoir, “Faith of My Fathers” (349 pages. Random House. $25). The book is meant to be a paean to his father and grandfather, both four-star admirals; a remembrance of his own grueling experiences in the Vietnam War, and, not coincidentally, the campaign biography of a candidate for president. The book amply demonstrates that McCain was a brave warrior and an honorable man. Whether it shows that McCain would make a good president is a more complicated question.

McCain’s faith, and the faith of his fathers, was taught at the U.S. Naval Academy. An “officer and a gentleman,” McCain explains, is “ransomed to his duty.” He trusts his fellow officers as brothers. He never “expects others to bear what he will not.” He admits his mistakes, never shifts blame and accepts punishment without complaint. Above all, he is brave. The one true test, which every officer longs for, is combat.

The McCains met that test again and again. Admiral McCain the grandfather led the legendary aircraft carrier Task Force 38 through swarms of kamikazes against the Japanese Navy. John McCain the father, a World War II submarine commander who sank tons of Japanese shipping, including a destroyer, endured depth-charge attacks so terrifying that the younger sailors in his sub were reduced to weeping in their bunks. As a naval aviator in Vietnam, John McCain III went on 23 bombing runs before he was shot down over Hanoi in 1967. On his last run, he held steady to deliver his bombs even though he could hear a Soviet-made SAM missile “lock on” to his plane. The missile tore off the plane’s right wing, and McCain ejected, breaking both arms and his leg.

McCain showed his true courage after his capture. Beaten bloody, he endured pain by blacking out. In June of 1968, after his captors had discovered that he was the son of the admiral of the U.S. Pacific Fleet, McCain was offered early release. Unwilling to leave before fellow POWs captured earlier, McCain declined and spent nearly five more years in brutal captivity.

The McCain men took to war as a calling. They seemed less comfortable with peace. As midshipmen they all compulsively defied discipline, finishing near the bottom of the class. As young officers, they brawled and boozed and sometimes neglected their families. For the youngest McCain, the ideal of fidelity did not always include marital vows. He has acknowledged (though not in this book) that he was “responsible” for wrecking his first marriage.

McCain loved, and was deeply loved by, his prison mates at the Hanoi Hilton. They soothed each other’s wounds and tapped out secret messages between jail cells. The scene McCain depicts of the POWs defying their captors with Christmas carols is heartbreaking. But McCain, now in his third Senate term, has been less warmly received by his fellow lawmakers in Congress, who respect him but generally regard him as a tempestuous and unpredictable loner.

Many Americans would welcome a politician with the integrity to stand up to the hacks. As president, McCain would undoubtedly try to shake up the “system,” particularly campaign finance. But presidents, like senators, have to know when to compromise, and McCain has never been known as a dealmaker. As for judgment–the most ineffable and important presidential quality–McCain’s book holds mixed clues. Great warriors are bold. McCain’s grandfather was feeling low at the end of World War II partly because he had just been relieved of his command–for allowing an American fleet to steam into a typhoon. In the less life-and-death arena of legislative politics, McCain the grandson seems to have the same damn-the-torpedoes instincts.

Still, McCain’s character has withstood tests the average politician can only imagine. McCain’s warrior virtues may become increasingly rare. Cautious policymakers and generals, armed with high-tech smart weapons, have tried to make war-fighting nearly casualty-free. (Senator McCain was a lone voice urging ground troops in Kosovo.) Young soldiers very rarely dodge bombs and bullets anymore. The Navy last fought a sea battle in 1945. John McCain comes from a line of warriors stretching back through all of America’s wars to ferocious Highland clans in Scotland. He may be the last of his kind.