The recent, deglorifying accounts of D-Day and after (John Keegan, Max Hastings) left untouched the repute of the British Sixth Airborne Division--one unit of which, the gliderborne troops of Major John Howard's D Company, made the first, crucial Normandy landing. For Ambrose, maximum-biographer of Eisenhower, this brief chronicle of a single engagement in a busman's holiday for fair: leading a veterans' battlefield tour in 1981, Ambrose was approached at Pegasus Bridge--one of the pair of crossings, over the Caen Canal and Ouse River, that Company D captured and held on D-Day--by none other than Major Howard . . . from whom (along with other British and German survivors) he later got much of this story. It's foremost a story of preparation. From the overloaded Horsa gliders soundlessly approaching their pinpoint landing zone at 0007 on D-Day, Ambrose switches to the preceding two years of training and planning, boredom and break-outs: Howard's fanatical emphasis on physical fitness and mental alertness; the endless nighttime simulations, the practice with German weapons; the intelligence, unprecedented in detail and currency (the scale model of the site was changed daily, on the basis of French-underground and aerial-reconnaissance reports); the sense, to a man, "that D-Day would be the greatest day of their lives." Howard's company succeeds in taking the bridges intact, thanks partly to luck and German weaknesses (a carousing officer, feeble non-German conscript troops). A single corporal, with the company's one functioning anti-tank weapon, holds the bridges until paratroop reinforcements arrive--in effect securing the invasion's entire eastern flank--while Hitler's insistence on giving every order delays a German counterattack until midday. But Howard loses his officers, by having them lead their platoons from the front. After D-Day, we learn, D Company reverted to being an ordinary infantry company, a waste Ambrose decries, and the British never mounted another such coup de main--"not for the bridge at Arnhem, nor the one at Nijmegen." Howard, a reckless driver, was seriously injured in a motor accident and crippled trying to get back into trim. Others of the men became friendly, even intimate, with their German counterparts (one of them now a British citizen). Ambrose is little given to dramatizing, and he apologizes for superlatives: recounted close-in, with soldierly affability and snap, the facts don't need embellishment.