The base at Bagram is used by special forces and as a prison
The hangars and buildings of Bagram airbase are a distinctive sight on the horizon on the drive from the Afghan capital, Kabul.
Originally built by the Soviet military during its invasion of Afghanistan in the 1980s, Bagram is now the main base for the US-led coalition force.
The base can hold up to 10,000 troops. It is under US command and control but forces from other coalition nations also use the facility.
Bagram also houses the main prison facility for people detained by US forces across the country, which can hold up to 1,000 prisoners.
The base, situated around 40km (25 miles) north of Kabul on the Shomali plain, has been occupied by the coalition forces since the toppling of the Taleban regime in December 2001.
It is officially known as Bagram Airfield by the US military.
It is served by a runway of more than 10,000ft (three-km), where large cargo and bomber aircraft can land and which has been repaired by coalition troops.
It played a key role during the Soviet occupation of Afghanistan, serving as a base for troops and supplies.
The airfield gets its name from the nearby Bagram village. Many of the village residents now work at the base.
Some of the troops situated there are involved in combat, but many supply the thousands of other US forces spread around the country.
Day and night, there is constant movement at the base.
Huge transport aircraft land or take off from there, and all kinds of helicopters can be seen, from Apache gunships and Chinook transport helicopters to Blackhawks.
Despite the heavy security, four detainees, described as "dangerous enemy combatants", escaped from Bagram in July 2005 - the first time any prisoner has managed to do so, the US military said.
Like the inmates of the US prison at Guantanamo in Cuba, the detainees were denied the right to challenge their detention in US civilian courts.
When this was overturned for Guantanamo detainees the US justice department sought to continue the practice in Bagram.
The prison at the Bagram air base houses senior al-Qaeda suspects
This was partially overturned in April, 2009 when a US judge, John Bates, decided non-Afghan prisoners held by American forces in Afghanistan could challenge their detention in the US.
People detained at Bagram are mostly held in an anonymous-looking building deep in the heart of the base, correspondents say.
Those who have been inside describe it as being divided up into cages in some areas, with walled-off rooms in others.
During the course of 2005, the US military gradually released many of those held there under a joint Afghan and US-backed reconciliation scheme known as the Takhim-e-Solh or "Strengthening Peace" programme.
Despite this initiative, after US President Barack Obama began his term in 2009 the justice department said around 600 people, including Afghan nationals and foreign al-Qaeda suspects, remained detained at Bagram.
The US is further planning to construct a $60m (?36m) new prison designed to hold 1,100 more people.
It is rare for attacks to take place on Bagram base but a rocket attack killed two US soldiers in June, 2009.
In February 2007 a suicide bombing outside the base during a visit by then US Vice-President Dick Cheney killed more than 20 people.