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

SSG James Avery/US Army

A soldier with the 10th Mountain Division guards a hallway during training for subterranean warfare.

• 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. 
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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.