After more than 50 years of development, "precision bombing" is still subject to mistakes - electronic, mechanical and human - that can exact a deadly civilian toll and can have far-reaching political consequences.
A bomb may fall off its aircraft rack prematurely; a loose tail fin may send it veering miles off course. The morning dew may briefly blind its laser-guidance system. Or a tired, stressed air crew member may punch the wrong target numbers into a satellite-guidance system.
After years of effort and billions of dollars in investment, today's bombing system "is a lot better, a lot safer" than in previous conflicts, said retired Admiral Stephen Baker, a former US Navy pilot and weapons tester. But he added: "It's not perfect."
And US officials are well aware that mistakes that result in civilian deaths could erode vital support for the US military effort from Afghan groups, allies in neighbouring countries and moderate Muslims elsewhere in the world.
The US effort to develop precision-bombing techniques became visible with the "smart bombs" of the Vietnam War era, and came into their own in the 1999 air war against Yugoslavia.
In the Balkan war, only 20 of the 23,000 munitions used by the US went awry and inflicted so-called "collateral damage", according to the Pentagon's official tally.
Yet those incidents brought worldwide attention - especially when a bomb fell on the Chinese embassy in Belgrade, the capital, killing three people - and repeatedly threatened to sunder the fragile European coalition that backed the NATO war effort.
The bombing of the embassy resulted from an erroneous US map, an example of how faulty intelligence can lead to such mistakes.
When the war was over, the Pentagon again intensified its effort to make its bombing techniques more precise.
Laser-guided bombs are the most precise of all, because they follow a thin beam to a precise point on the ground. Yet they can be thrown off by rain, clouds or even heavy fog or dust.
Such bombs are often used by tactical fighter jets that aim a laser beam on a target as the aircraft fly at 500 miles per hour at low or medium altitude. The systems can also be knocked off if the aircraft hits turbulence.
On other occasions, smoke from the explosion of one bomb will drift in front of a second target, interrupting the laser beam and throwing off the bomb, said Admiral Baker, now an analyst with the Centre for Defence Information think-tank in Washington.
A number of mechanical glitches can cause a bomb to be dropped on the wrong target. Racks holding the bombs under the wings of a fighter jet sometimes fail, releasing the weapons prematurely. No laser system would be able to correct inadvertent drops, analysts said.
The military has spent billions of dollars over the years trying to automate target systems in ways that would make them less subject to glitches.
In the Vietnam War, targeting information was passed between controllers and pilots and headquarters in a system that was labour intensive and subject to occasional errors.
Now the process has been computerised. Yet humans are called on to perform several tasks.
They can make mistakes, as occurred in mid-October when a US service member apparently transposed two digits in targeting data. The mistake sent a 2,000-lb bomb crashing into a row of homes in Kabul, killing at least four people.
Errors can also occur during the complicated process of converting maps into numerical targeting data, a process called "co-ordinate drift".