Our mania for anniversarizing has taken us well past D-Day, and already we are beating the drums for the 40th anniversary of Yalta, Hiroshima, V-J Day, etc. So this short, stark little book may seem to have missed the parade.

Not to worry. It will be read.

It is about the glider landing of a handful of Britons on the coast of France six hours before the gigantic invasion of June 6, 1944. Had these men not seized intact -- and held -- two small bridges just beyond the left flank of the landing beaches, German tanks could well have rolled up the entire invading force.

The bridge over the Caen Canal, well known to the British as Pegasus Bridge, ranks right up there with Remagen and Arnhem, according to Ambrose, who has also written a two-volume biography of Dwight Eisenhower and who welcomed the chance to examine at close range this single brick in the vast edifice of World War II.

Examine is the word. Along with the brief lives of the key figures in this action, both British and German, Ambrose provides a copy of D Company's marching orders, the incredibly detailed topographical report available to the invaders, and not only a map showing exactly where the gliders landed but even Maj. John Howard's sketch of his plan for disposing his meager forces.

After a rather deliberate opening that sets the stage for this intricate coup de main, including Howard's fanatic training program and elaborate rehearsals, the real story begins. From the point when the first clumsy wooden Horsa glider crash-lands precisely on its peapatch target, it is a riveting tale. Minute by minute, hour by hour, the danger grows.

"Brotheridge, almost across the bridge, pulled a grenade out of his pouch and threw it at the machine gun to his right. As he did so, he was knocked over by the impact of a bullet in his neck. Just behind him, also running, came Billy Gray, his Bren gun at his hip. Billy also fired at the sentry with the Verey pistol, then began firing toward the machine guns."

Panzer tanks moved in, counterattacking against the fragile outpost. Company D had only one operative antitank weapon. A Nazi gunboat crept up the canal. The promised paratroop reinforcements were nowhere in sight. Enemy snipers got the range.

Meanwhile, Col. Hans von Luck of the 125th Panzers was desperate to launch his heavy tanks and overrun the lightly held position. But he had to wait for Hitler's personal approval. And Hitler was still asleep; his staff was afraid to wake him.

At last the tanks rolled. The British sergeant with the lone Piat antitank gun waited for them to get into his 50-yard range. "And sure enough, in about three minutes, this bloody great thing appears. I was more hearing it than seeing it, in the dark; it was rattling away there, and it turned out to be a Mark IV tank coming along pretty slowly, and they hung around for a few seconds to figure out where they were. Only had two of the bombs with me. Told myself, 'You mustn't miss.' Anyhow, although I was shaking, I took my aim and bang, off it went." The single shot penetrated the tank and set off its ammunition, destroying it and sending the other tanks scurrying.

Luck was with the invaders. Hitler wasn't the only heavy sleeper. German bridge guards were routed out of their beds deep in their bunker. Many of the defenders were Polish or Russian conscripts, who lacked not only the German language but the will to fight. Ambrose makes the point that this was Germany's basic problem in the war: it had overreached itself and was forced to use poor-quality soldiers just when it most needed good ones.

With his plain, laconic prose, the author manages to get across a number of wry observations about the vicious little battle, the invasion, World War II and war itself. Lord Lovat, leading some commandos in relief of Company D, does not come off well at all. He insists on marching his men across the exposed bridge in their red berets -- and wastes a dozen casualties. (This was an army that forbade its soldiers the use of steel helmets throughout the entire first year of World War I.)

Furthermore, the army squandered this uniquely trained, elite group, who might have gone on to seize intact other bridges on the road to Berlin. At Arnhem, for instance. Instead, Company D was left in place for two months, like any ordinary infantry unit, until its original strength of 181 was bled to 40.

"Pegasus Bridge" tells a lot in a little. A gem.