Hollywood films often show alien ships or giant monsters rising from the ocean depths to threaten humanity's existence. The U.S. military envisions a more realistic scenario of hiding robotic drones, sensors or decoys on the ocean floor so that they can rise to the occasion when needed.

The idea of hiding sneaky spy technologies beneath the waves comes from the U.S. Defense Advanced Research Projects Agency. The agency described its Upward Falling Payloads program as an effort to hide underwater capsules that could be triggered remotely to activate, float to the surface and release their payloads of sensor buoys or even flying drones.

"The concealment of the sea also provides opportunity to surprise maritime targets from below, while its vastness provides opportunity to simultaneously operate across great distances," DARPA said in a broad agency announcement on Jan. 11.

Earth's oceans provide plenty of hiding places for robots to engage in some "cheap stealth" — about 50 percent of the oceans reach depths deeper than 2.5 miles (4 kilometers). DARPA's ideal payload would fit within a spherical capsule 17 inches in diameter or a cylinder about 5 inches in diameter and 36 inches in length.

The idea of deploying robots from beneath the waves has some precedent, given how the Navy has tested the launch of flying drones from a submarine's trash chute. By comparison, the Upwards Falling Payloads effort faces the additional challenges of ensuring robotic technologies can hibernate for years under deep-ocean pressure and still obey instantly when the order comes down to activate.

DARPA emphasized that the new program is "specifically not a weapons program" and would have "non-lethal" intent. "But other countries may have a different opinion on the definition of "non-lethal" for robots or drones deployed to carry out surveillance or jam communications."

The new program highlights the U.S. Navy's turn to a growing swarm of robotic ships and flying drones that can supplement traditional warships and aircraft. Recent experiments have included firing missiles from robot boats, deploying drone helicopters such as the MQ-8 Fire Scout to help track pirates or smugglers, and testing the X-47 robot warplane from the deck of an aircraft carrier.

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DARPA has also funded development of larger robot ships, such as a submarine hunter called the Anti-Submarine Warfare Continuous Trail Unmanned Vessel, which can stay out at sea for up to 90 days.

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