If any nostalgics still doubt the wisdom of the British in abandoning their empire without much of a fight, let them read “The Last Valley” (Da Capo Press, 734 pages, $30). In 1945 France was a ruined nation. Her self-respect had been destroyed by defeat in 1940 even more disastrously than her armies.

French leaders, French soldiers, the French people were determined that there should be no more humiliations. Thus they embarked upon disastrous campaigns to preserve the French empire from nationalists, which began in Saigon in 1945 and ended in Algiers almost two decades later.

The story of the French war in Indochina was told in English vividly, but in frankly sensationalist fashion, by Bernard Fall 40 years ago. Now, Martin Windrow has eclipsed Fall with his meticulous and magnificent account of the tragedy, which reached its nadir at Dien Bien Phu in May 1954,followed by French withdrawal from Vietnam three months later.

France’s commander in Indochina, General Henri Navarre, was dispatched from Paris in May 1953 not with a mandate to win the war – such a goal had plainly become unattainable – but instead to create conditions for an honorable peace. Navarre believed these could be achieved only by first punishing the enemy’s conceit. The Vietminh were pouring weapons and supplies into the country from China and everywhere pressing French garrisons.

Navarre and his staff conceived a plan to drop two brigades of paratroops into Dien Bien Phu, one of the only valleys in the region where air landing was possible, then to build up a powerful base there, from which the enemy’s guerrillas could be pursued and pounded. They were over-impressed by the precedent of the British wartime Chindits in Burma and failed to notice that most serious military analysts deemed the Chindits’ creator, Orde Wingate, to have been a dangerous madman.

The initial drop was a success. Reinforcements poured in, to achieve a strength of 12 battalions. Yet through the last months of 1953 and the first of 1954, the Communists, too, reinforced heavily. Confounding all French expectations, instead of fleeing from the firepower of a modern conventional army, these barefoot soldiers determined to engage it.

By prodigious human exertions, they dragged their own artillery and ammunition 500 miles from the Chinese border and placed it in caverns hewn from the hills around the French base. Thousands of Vietminh infantry marched through the jungle amid terrible privations to join General Nguyen Giap’s siege. With increasing energy and strength, they began one by one to assault the hills on which the defense rested, so innocently christened Gabrielle, Anne-Marie, Beatrice, Dominique, and suchlike. And one by one, despite appalling Vietminh casualties, these positions collapsed.

It is a shocking story. The French embarked on the encounter with more than 10,000 men, asserting confidently as late as March 1954: “We’re going to show them!” Yet for all its courage and fighting skills, the French garrison was not a modern, high-tech force. Navarre was attempting to hold Indochina with ageing World War II equipment and aircraft and nowhere near enough of them.

The Foreign Legion battalions fought superbly at Dien Bien Phu, but many of the colonial units – Moroccan, Algerian, Thai – did not distinguish themselves. Their commander, Colonel Christian de Castries, was a 54-year-old cavalry officer whose initial braggadocio was translated into gloomy paralysis as his perimeter shrank.

French air support was too feeble to decisively influence the battle. Air Force blunders included dropping new maps showing the latest French and assumed Vietminh positions into the arms of Giap. When Vietminh artillery fire closed the airstrip and the garrison became dependent on air-drops, each day the wretched airmen had to provide at least 40 Dakota-loads to maintain supplies, above all artillery ammunition. The threadbare French pleaded with the rich Americans for help, mostly in vain, but the United States did provide 60,000 parachutes.

By April, the French “Operation Castor” launched with such hubris, had languished to the point at which hapless gunners were meeting massed Vietminh assaults with the terrible order: “Debouchez a zero!” – “Point blank!” Even during “quiet” spells, the defenders suffered 50 casualties a day. When there were no more trained paratroopers, 700 volunteers were dropped with no jump-training at all to reinforce the garrison.

The airmen found it more and more difficult to land supplies in their own lines. De Castries signaled his headquarters acidly on April 13: “In 24 hours we have sustained three [French] bombing attacks. … On the other hand the cargo of three C-119s, or a minimum of 800 artillery rounds, has been delivered to the enemy. No comment.”

The Vietminh squeezed the French perimeter yard-by-yard, day-by-day, driving their trenches and saps towards the defenders’ lines in exactly the fashion of Medieval besiegers. Communist casualties were far beyond anything a Western army would have endured. But the Vietminh could pay the blood-price more easily than exhausted France.

Of 15,000 men who defended Dien Bien Phu, some 3,600 died in action or as captives and almost 4,400 were wounded before May 7, 1954, when the survivors surrendered. Some 9,000 of de Castries’s men then became prisoners. During just four months before they were repatriated, so appalling was their captors’ brutality that around half died.

It is hard to praise too highly Martin Windrow’s account, the first work of a historian who obviously possesses great gifts. It is surprising how many writers who describe battles lack any understanding of tactics and technology. Mr. Windrow is master of every detail.

North Vietnamese sources are still very limited, but he has made the most of what exist. His book makes gripping reading. I hope he writes a lot more.

Mr.Hastings is the former editor of the Daily Telegraph, where this article first appeared. His latest book is “Armageddon: The Battle for Germany 1944–5.” (Alfred A. Knopf).