Researchers say a drone aircraft being tested by the U.S. Navy that could conduct a combat mission without human involvement raises troubling ethical questions.

The drone, designed to land on the deck of an aircraft carrier, operates not only with no pilot in the cockpit but with no pilot at all, raising the specter of a pre-programmed semi-independently operating machine capable of wreaking mayhem on its own.

While humans would program the autonomous drone's flight plan and could override its decisions, many find the concept of a heavily armed aircraft operating without direct human control worrisome.

"Lethal actions should have a clear chain of accountability," Noel Sharkey, a computer scientist and robotics expert, told the Los Angeles Times. "This is difficult with a robot weapon.