Part 2
Charles Heyman, the editor of Jane's World Armies, said: "It would be a very difficult operation, there is no doubt about that. Commanders will want a lot of troops and aircraft as well as artillery in support because many defences may still be in place after air strikes.
"The classic terrorist tactic is to desert these places and move away and not get themselves caught by properly organised military forces of any sort. But if there are people trying to defend them, you could have a really bloody battle on your hands."
Contingency plans for airlifting casualties out of the battle zone will also be necessary. American strategists are drawing on the experiences of the "tunnel rats" of the Vietnam War, the US soldiers who, armed with grenades, pistols and torches, fought in the hundreds of miles of tunnels dug by Communist guerillas.
While military technology has moved on, with thermal imaging equipment used to track enemies, the battle would come down to the same techniques of hand-to-hand fighting in claustrophobic conditions.
The terrorists' tunnels are believed to be able to conceal thousands of fighters for months. They include dormitories and other living quarters, communication centres and armouries stacked with Kalashnikov rifles, mortars, ammunition and explosives.
Some of the caves have lighting and electricity supplied by generators and makeshift systems of hot water pipes for heating. Al-Qaeda fighters live a sparse existence with just the Koran for comfort.
Bin Laden was known to be based in a cave in a mountain range above Jalalabad in eastern Afghanistan, the subterranean centre of his global terror network, until disappearing before the US hijack attacks.
His underground lair was reported to have a library of Islamic texts, an arms store and a communication room including computers, faxes and a satellite telephone.