Imagine wars where weapons can make their own decisions. Well, your imagination can someday turn into a reality - thanks to scientists who have developed a new software that they claim is a step towards getting robotic aircraft to make their own, ethical decisions about wielding lethal force.

A team, led by Ron Arkin at the Georgia Institute of Technology, has developed an "ethical governor", which aims to ensure that robot attack aircraft behave ethically in combat, and is demonstrating the system in simulations based on recent campaigns by US troops, using real maps from the Middle East.

In one scenario, modelled on a situation encountered by US forces in Afghanistan in 2006, the drone identifies a group of Taliban soldiers inside a defined "kill zone". But the drone doesn't fire. Its maps indicate the group is inside a cemetery, so opening fire would breach international law.

In another scenario, the drone identifies an enemy vehicle convoy close to a hospital. Here the system only allows fire that will damage the vehicles without harming the hospital. The team has also built in a "guilt" system which, if a serious error is made, forces a drone to start behaving more cautiously.