In the decades since the end of the Korean War, Pyongyang has constructed thousands of tunnels, Army Brig. Gen. Neil Tolley, commander of U.S. Special Operations Forces in South Korea, said at a conference in Florida last week. Tolley said the tunnels include 20 partially subterranean airfields, thousands of underground artillery positions and at least four tunnels underneath the Demilitarized Zone separating the two Koreas. “We don’t know how many we don’t know about,” Tolley said.

“The entire tunnel infrastructure is hidden from our satellites,” Tolley added. “So we send [Republic of Korea] soldiers and U.S. soldiers to the North to do special reconnaissance.” Tolley said the commandos parachute in with minimal supplies in order to watch the tunnels without being detected themselves.

Update: The article at the Diplomat is gone and reporter David Axe is being told that he misheard what Tolley said. Apparently Tolley was speaking hypothetically, not describing actions already taken. Axe insists it was ambiguous:

I told The Diplomat I will step down as a regular contributor. I want to spare them any additional damage. But let me be clear: Tolley did not state that he was speaking hypothetically. And he described in detail his need (either at present or eventually, conditionally — he did not specify) to “leap” forces north with ever-lighter and better equipment. I’m told that represents a present or potential violation of the Koreas’ armistice. Which, apparently, USFK takes very seriously … though Pyongyang does not.