DARPA is asking universities for access to their tunnels ASAP, and it's because the US military thinks its next war will go underground

A soldier with the 10th Mountain Division guards a hallway during training for subterranean warfare. SSG James Avery/US Army The Defense Advanced Research Projects Agency (DARPA) tweeted on Wednesday that it was seeking "university-owned or commercially managed underground urban tunnels & facilities able to host research & experimentation," raising concern from Twitter users.

DARPA's request is actually related to the Pentagon's focus on underground warfare in large urban spaces, which it's devoted at least half a billion dollars to since 2017.

The agency told Insider that the request was also related to its SubT Challenge, where teams of researchers show off technology they develop to assist in searching, mapping, and navigating underground spaces.

Visit Business Insider's home page for more stories. The Defense Advanced Research Projects Agency (DARPA) issued a peculiar request over Twitter on Wednesday, asking for underground tunnels to use for research - as soon as possible. Though DARPA's request managed to spook Twitter users, DARPA told Insider that the request is related to technology development for underground combat and search-and rescue operations. While President Donald Trump looks to create a Space Force - an entirely new military branch - the Pentagon itself has put more than half a billion dollars into technology and training to compete on underground battlefields.

The Defense Advanced Research Projects Agency asked universities and colleges for underground tunnels to use for research. Staff Sgt. Michael Armstrong / US Army / DVIDS "Attention, city dwellers," DARPA tweeted. "We're interested in identifying university-owned or commercially managed underground urban tunnels & facilities able to host research & experimentation." The agency noted the short notice of the request - it asked for responses within two days - and specified that it was seeking "a human-made underground environment spanning several city blocks" which includes "a complex layout & multiple stories, including atriums, tunnels & stairwells."

While the Trump administration is increasingly looking to the skies and pressing for a Space Force, DARPA is focusing on operations underground. Stacy Smenos, Dugway Proving Ground / DVIDS In the agency's online request for information, DARPA specifies that it's trying to understand how technology could be used for rapid mapping, search, and navigation operations, likely in the case of urban conflict or disaster-related search-and-rescue operations. "Complex urban underground infrastructure can present significant challenges for situational awareness in time-sensitive scenarios, such as active combat operations or disaster response," Jared Adams, a spokesperson at DARPA, told Insider via email.

The request comes out ahead of DARPA's Subterranean Challenge. Matt Gonzales / US Marine Corps / DVIDS The Subterranean Challenge, or SubT Challenge, invites teams of researchers from all over the world to compete and find technological solutions for underground operations. The teams use locations - like the ones DARPA requested information about - to test technologies that can search and navigate in underground terrain where it might be too difficult for humans to go. Teams in the systems competition focus on technology like robotics that can physically search and navigate in an underground terrain. On the virtual track, teams compete and develop software that can be used to assist in simulations of underground operations.

The urban circuit of the SubT challenge will take place in February 2020, hence the request for urban underground space. Capt. Scott Kuhn / DVIDS "As teams prepare for the SubT Challenge Urban Circuit, the program recognizes it can be difficult for them to find locations suitable to test their systems and sensors," Adams told Insider. "DARPA issued this RFI in part to help identify potential representative environments where teams may be able to test in advance of the upcoming event."

The military has become more aware that it needs to develop technology and strategy to fight in an underground, urban setting. Sgt. Jessica DuVernay / DVIDS Historically, underground warfare has been the domain of special operations troops like Navy SEALs. But military researchers predict that this kind of warfare will be too much for special operators alone to navigate, particularly if dealing with an adversary like China or Russia, which both have extensive underground space. China in particular uses vast underground complexes to store missiles and its nuclear arsenal. "We did recognize, in a megacity that has underground facilities - sewers and subways and some of the things we would encounter ... we have to look at ourselves and say 'OK, how does our current set of equipment and our tactics stack up?'" Col. Townley Hedrick, commandant of the infantry school at the Army's Maneuver Center of Excellence at Fort Benning, Georgia, said in an interview with Military.com last year.