Hundreds of US soldiers have established their northernmost base in Afghanistan, pushing up along its eastern border with Pakistan to block militants crossing jagged mountains, train fledgling local forces and build support with wary tribesmen.
In doing so, they have pushed themselves further into harm's way, drawing rocket fire from enemies on surrounding mountain peaks and losing at least seven soldiers since February, including their previous commanding officer in a May 5 helicopter crash in bad weather.
With NATO taking charge of security in the volatile southern provinces wracked by a Taliban resurgence, the US is increasingly able to focus on stabilising the still-dangerous east of Afghanistan, extending the Afghan government's writ there and hunting for fugitives like Osama bin Laden.
More than 600 US soldiers have deployed in Naray, a clutch of mud-brick and stone villages inhabited by 30,000 Pashtun tribes-people in Kunar province -- a virtually forgotten corner of Afghanistan at the northern end of the belt of eastern provinces patrolled by US forces.
Bin Laden is familiar with Kunar's mountainous terrain from the days of the holy war against the 1979-89 Soviet occupation of Afghanistan.
The province was also a stronghold of Afghan warlord, Gulbuddin Hekmatyar, whose Hezb-e-Islami faction has long held ties with bin Laden and now fights the elected government of President Hamid Karzai.
American officials say heavily armed remnants of Hekmatyar's group are still active in Kunar and receive aid from militants crossing into Afghanistan from lawless tribal regions in Pakistan.
They are also supported by holdouts from the Taliban regime, which was toppled in late 2001 by US-led forces for harbouring bin Laden, orchestrator of the Sept 11 attacks.
But Lt Col Michael Howard, commanding officer of Forward Operating Base Naray, said the main challenge his American forces face is not the virtually impossible task of sealing the frontier from militant incursions but winning the trust of villagers from five local tribes.
"You have a group of people who for years have had one option, and that was to cower to, or be a part of the likes of the Taliban, Hezb-e-Islami or Al-Qaeda.
That was their only choice," said Howard, who runs the 3rd Battalion, 71st Cavalry Regiment of the 10th Mountain Division, based in Fort Drum, New York.
"The greatest challenge is making folks realize that things have changed."
Some soldiers in Naray have recently arrived from southern Helmand and Kandahar provinces, where NATO has deployed thousands of forces in recent months -- mostly British and Canadians -- and last week took over command from the US-led anti-terror coalition.
More US soldiers are expected to be shifted to the east in the months ahead.