The French military experience in Algeria 50 years ago has left an indelible mark on a new generation of US officers, who have tried to apply the lessons of the conflict to the fight against insurgents in Afghanistan and Iraq.

As France marks the 50th anniversary of a war that remains a bitter memory, the strategy and tactics employed by French forces have enjoyed a revival inside the US military.

After quickly toppling regimes in Baghdad and Kabul, American commanders were caught off guard by virulent insurgencies in both countries that posed a challenge to a force trained only for conventional combat.

"It is not unfair to say that in 2003, most Army officers knew more about the US civil war than they did about counterinsurgency," John Nagl, a retired colonel who served in Iraq, wrote in the foreword to the army's manual on irregular warfare.

Facing a politically savvy adversary seeking to exploit resentment of foreign troops, US military officers saw parallels in the Algerian war.

In August 2003, the Pentagon organized the showing of the 1966 film "The Battle of Algiers," the Gillo Pontecorvo movie that recounts operations in the Casbah, including the torture of guerrillas by the French.

"How to win a battle against terrorism and lose the war of ideas. Children shoot soldiers at point-blank range. Women plant bombs in cafes. Soon the entire Arab population builds to a mad fervor. Sound familiar?" read a Pentagon flyer for the screening.

Encouraged by senior officers such as General David Petraeus, who served as commander in Iraq and Afghanistan before leading the CIA, the French counter-insurgency doctrine honed in Algeria was gradually rediscovered and promoted.

Petraeus oversaw the writing of a new field manual for counter-insurgency in 2006 that drew heavily on the Algeria era and one French strategist in particular, Lieutenant Colonel David Galula, author of "Counterinsurgency: Theory and Practice."

Galula's book, published first in the United States in 1964, enjoys prominent references in field manual 3-24 and is cited as a "classic" in the bibliography.

"Of the many books that were influential in the writing of Field Manual 3-24, perhaps none was as important as David Galula's 'Counterinsurgency Warfare: Theory and Practice,'" Nagl wrote.

Reflecting Galula's ideas, American troops conducted sweeps through urban areas, sought to cut off insurgents from the population, trained local forces and pored over intelligence to identify the leaders and motivations of the insurgency.

US strategists also frequently cite "Modern Warfare" by Colonel Roger Trinquier, a veteran of the Algeria war who was critical of his own army's slow adaptation to new tactics.

Trinquier, however, openly advocated torture as a means of extracting vital information from guerrillas. The US counter-insurgency manual explicitly prohibits abusing prisoners, saying the practice plays into the hands of insurgents and undermines America's "moral legitimacy."

Both Trinquier and Galula "captured with considerable nuance the conduct of counter-insurgency operations of that day, and a good bit of the way those operations were conducted remains instructive and relevant," Petraeus wrote in an email to AFP.

As head of the Command and General Staff College, Petraeus ordered the purchase of the English translation of Galula's work and had a copy issued to every one of the more than 1,200 students at the college, he said.

Petraeus and other soldiers have found kindred spirits among their French counterparts in the Algerian war, at least as they are portrayed by French writer and journalist Jean Larteguy in his 1960 novel "The Centurions."

The book, which enjoys a near cult following among American officers, portrays the trials of French paratroopers in Indochina and Algeria who learn to fight insurgents in spite of their own military's bureaucratic mindset.

"For our sort of war," the main character Pierre Raspeguy says, "you need shrewd, cunning men who are capable of fighting far from the herd, who are full of initiative too... who can turn their hand to any trade, poachers and missionaries."

Director of the Pakistan Afghanistan coordination cell, Major General Ben Hodges told AFP in an email he had first read the "excellent book about the French experience coming out of Indochina and then going into Algeria" as a cadet at West Point in the late 1970s.

"I decided to read it again because of my recent deployment to Afghanistan... Some very thought-provoking parts to the story and the impact on the soldiers involved."