The U.S. Defense Department is looking to nature for inspiration and hopes to develop a super-smart drone that can hunt like a hawk, even indoors.

The department's Defense Advanced Research Projects Agency (DARPA) has put out a call for researchers to participate in developing autonomous drones small enough to fly into a building through an open window and support troops engaged in dangerous urban missions.

The drone needs to be able to fly indoors at speeds up to 45 mph, automatically navigating through complex indoor environments without communication with outside operators, DARPA says.

The inspiration for the Fast Lightweight Autonomy program -- yes, that's FLAP -- comes from nature in the form of the goshawk, a bird of prey with the unique ability to fly through dense forests without "smacking into a tree," says program manage Mark Micire.

What DARPA is asking researchers for is an autonomy algorithm that would let a drone mimic the birds' ability to fly fast while still avoiding obstacles, all without human control or intervention.

Small drones for indoor flight have been developed before, but all have required human controllers and have navigated using GPS.

DARPA envisions a drone that would still be operated by a pilot who could be thousands of miles away, but which could be able to make split-second decisions on its own to avoid obstacles and navigate indoors.

The drone would search an area carrying cameras, microphones and other sensors and navigate, without assistance, a "labyrinth of rooms, stairways and corridors," DARPA said in a release announcing the project.

Birds of prey and many kinds of flying insects have the kinds of navigational capabilities DARPA is seeking for such drones, Micire says.

"The goal of the FLA program is to explore non-traditional perception and autonomy methods that would give small UAVs the capacity to perform in a similar way, including an ability to easily navigate tight spaces at high speed and quickly recognize if it had already been in a room before," he says.

DARPA says it intends to grant a number of contracts and grants worth $5.5 million in its FLAP initiative.

Technology developed in the program could have applications beyond military operations, says Stefanie Tompkins, director of DARPA's defense sciences office.

"Urban and disaster relief operations would be obvious key beneficiaries, but applications for this technology could extend to a wide variety of missions using small and large unmanned systems linked together with manned platforms as a system of systems," she says.