One in an occasional series.

PECH RIVER VALLEY, Afghanistan - The soldiers of C Company huddled around the radio as the bad news spread: Insurgents had ambushed a platoon about 10 miles upriver, killing the turret gunner of an armored humvee.

"One KIA," said First Sgt. John Mangels, a 20-year veteran, swearing under his breath. "One wounded."

A quiet rage ran through the main camp in eastern Afghanistan that day, Aug. 17. Army Capt. Robert Stanton, the company commander, hovered over a topographical map with one of his platoon leaders, jabbing at routes the Taliban might take to flee into the Hindu Kush mountains.

The Americans' instincts told them to strike back with great force - to send a strong message to anyone associated with the militants who had set up the ambush. But their training instructed them to retaliate only when the time was right, at precisely the right target - that winning over the population was just as important as killing the enemy.

"A lot of Afghans are sitting on the fence," said Mangels, 43, who has also served in Iraq. "If you are careful, they see that, and they come to your side. But if you kill the wrong people, it's damage that takes months - years - to recover from."

Five years after America launched the war on terrorism here after the 9/11 attacks, the battle in Afghanistan has evolved into a protracted counterinsurgency campaign stretching along much of the 1,500-mile Pakistani border, where resurgent Taliban forces live among the Afghans or find sanctuary in tribal areas across the border.

U.S. conventional military forces, trained to employ shock-and-awe power, have retooled for a more sophisticated mission. For a year before C Company and the other units of the 10th Mountain Division's Third Brigade Combat Team were deployed to Afghanistan in March, even the lowest infantryman was drilled in the new doctrine. The soldiers learned Afghan language, culture and history. No more calling the enemy Haji - not when the Afghan government that the Americans are supporting is Muslim, too.

"We are trying to advance the state of the art in counterinsurgency here," said Col. John W. Nicholson Jr., the brigade commander whose forces are stationed in eastern Afghanistan.

But the mission is difficult and frustrating, particularly when the Taliban get infusions of money, recruits and arms from outside Afghanistan. The enemy is clever and elusive, preferring to fight from afar, using rockets or improvised explosive devices (IEDs).

"Whenever they attack us directly, we win," Mangels said. "But they fire rockets at us, and they run. Or they leave IEDs. They're like ghosts out there."

While NATO troops fighting in Afghanistan's southern deserts have received much attention, Americans are dying here in mountainous eastern Afghanistan. It's the forgotten front in a forgotten war.

Of 28 coalition deaths in Afghanistan in the last month - 10 Americans, eight Britons, eight Canadians and two French - a quarter occurred here in Konar and Nurestan provinces, a few miles from Pakistan.

In a little more than a week in August when an Inquirer reporter and photographer were embedded with forces, seven Americans died in engagements near the Pech valley.

This is the territory of the First Battalion, 32d Regiment - one of the Third Brigade's light infantry battalions now deployed in eastern Afghanistan. During six months in Afghanistan, the 1-32 has taken more casualties than it did during its yearlong deployment to Iraq.

"When I first came to Afghanistan, I actually thought it was more of a peacekeeping mission at the time," said Pvt. Adam Boguskie, a humvee gunner from Kentucky. "I couldn't have been more wrong."

Into the teeth of al-Qaeda

The Afghanistan government has never exerted much control in the severe highlands of Konar and Nurestan, where the mountains contain some of Afghanistan's only forests. Nurestan, the more northern province, is so isolated that its inhabitants converted to Islam only in the 19th century, more than a thousand years after the rest of the country.

This region traditionally has been governed by tribal groups, who conspire with smugglers and insurgents to transit arms and fighters on narrow footpaths that thread through the valleys. Before the Taliban fell, Islamic militants trained here without much risk of detection. Even after the Americans in 2002 established a base in Konar's capital, Asadabad, coalition control did not extend far beyond the wire.

"The terrorists who attacked the Trade Center were trained up here," said Stanton, the C Company commander. "It's a traditional safe haven for al-Qaeda... . They're here, they're in the country, they're very prevalent, and they don't want us here. More specifically, they don't want the government of Afghanistan to succeed."