Instead of homing in on Taliban regulars along the confrontation lines with the opposition Afghan Northern Alliance, US bombers initially focused on units of the 500-strong "55th brigade", a formation of battle-hardened Arab fighters.
By selectively targeting the "Arabs", Washington had hoped to send a message to Taliban commanders and militia that the anti-terror campaign was against Osama bin Laden, the alleged mastermind of the attacks on the US, and his al-Qaeda organisation rather then the Afghan regime and people.
The aim of this strategy was to encourage Taliban officers and troops to defect to the Northern Alliance or depart the field of battle. So far this has not happened.
Indeed, many ordinary Afghans have rallied to the Taliban cause as have 9,000 Pakistanis, who are waiting at the border for the Taliban to induct them into their army.
The 55th brigade, based at a former Afghan army facility outside Kabul, was raised, trained and paid for by bin Laden.
Its units are said to be better trained and more highly motivated than Taliban troops. The 55th is drawn from the estimated 3,000 Arabs and others who have settled in Afghanistan.
Many are Islamists who dare not return to their home countries, others stay on in Afghanistan because constant warfare provides employment.
The 55th is a regular infantry formation, not an underground terrorist organisation like bin Laden's al-Qaeda.
During the war against the Soviet Union more than 25,000 volunteers joined the Afghan mujahedeen ("holy warriors"), including Arab Saudis, Egyptians, Algerians, Sudanese, Yemenis, Somalis, Lebanese and Mauritanians and non-Arab Chadians, Indonesians, Filipinos, Uzbeks, Tajiks and Uyghurs from western China. Since then veterans, known as "Afghans", have fought in the conflicts in Bosnia, Kosovo, Kashmir and Chechnya and mounted challenges to their own governments in Algeria, Egypt and Uzbekistan.
More than 1,000 seasoned "Afghans" and fresh mercenaries have crossed the border into Afghanistan since September 11th.
The 55th brigade has provided crucial support to Taliban forces during offensives against the Northern Alliance over the past five years.
Once the US bombing campaign began, units of the 55th were dispersed to strategic positions round the country to await the expected Anglo-US ground campaign.