THE US army plans to protect its helicopters with a laser weapon designed to dazzle anyone attempting to shoot at them from the ground. But the development has prompted concerns over whether such lasers could cause permanent blindness.

The device, called Aircraft Countermeasures (ACCM), consists of a laser that can be mounted alongside other weapons to protect the helicopter from small-arms and machine-gun fire without using lethal force. Small-arms fire is an increasing threat to helicopters, and the US army recently reintroduced door gunner training for the first time since the Vietnam war, using a new virtual-reality training system. But existing electronic countermeasures only protect against guided missiles.

The ACCM is being developed at Kirtland Air Force Base in New Mexico by ScorpWorks, the Air Force Research Laboratory's tactical laser prototyping team. In 2004 the team tested a laser dazzler against a shooter firing a simulated rifle at ranges of ...