For Dungeons & Dragons roleplayers, part of the fun of make-believe adventure is searching for hidden chambers where the monsters keep their treasure. For that matter, it's a familiar theme in horror movies to have villains and vampires pop out from behind walls and bookcases.

But for U.S. commandos, hidden compartments are not entertainment. They are obstacles to a successful mission to capture fugitives, or seize documents and weapons. And on a house raid in hostile territory, there isn't a lot of time to go tapping on walls to find a stash.

That's why U.S. Special Operations Command (SOCOM) wants a detector that can quickly spot where the loot is hidden. The goal of the research project is to develop a handheld device that can detect hidden chambers in an average-sized room (168 square feet) and at a range of about 6.5 feet during sensitive site exploitation, or SSE, operations.

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The sensor should be able to penetrate to a depth of 2 feet and have enough battery power to run for forty to fifty minutes. However, while it needs to detect hidden spaces, it doesn't need to scan the contents inside. “It doesn't have to 'see' thru a metal surface/container; the presence of a metal chamber in a wall would be a suspicious indication,” SOCOM says.

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Sensors that detect the presence of humans, such as infrared, acoustic or radar, already exist or are being developed. But current technology is either too bulky or too complicated, says SOCOM. But developing a handy device poses technical challenges. SOCOM emphasizes that the sensor must be able to distinguish between normal spaces in a wall, such as the gap between studs, and hidden compartments. It also must be able to function with a variety of building materials, including brick, cinder block, concrete, wood and sheet rock. “The system should be able to distinguish suspicious hidden cinder block openings vs normal cinder block voids in normal wall construction,” SOCOM adds.

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And the device has to be easy to use and reliable. “For the operator to be willing to carry/operate an additional system, along with all of his other equipment, the system performance needs to be high; a system with low detection rates or high false detection rates will be left behind,” SOCOM points out.

SOCOM suggests that cutting-edge technologies such as modern radio frequency transmit/receive modules, advanced computer vision algorithms and modern computer processors may enable a solution to be found. The research proposal did contain links to a Wikipedia entry on ground-penetrating radar, and a Florida company called Ground Hound Detection Services that detects the presence of underground utilities before construction begins in an area.

Michael Peck is a contributing writer for the National Interest. He can be found on Twitter and Facebook.

This article first appeared in 2017. It is being republished due to reader interest.

Image: National Museum of the U.S. Navy via Wikimedia Commons