The U.S. Forces Korea conducted special training last weekend to practice seizing a North Korean nuclear facility buried deep underground.
The USFK publicized the drill on Twitter to send a warning to Pyongyang, just before North Korea staged a massive military parade on Monday where it showed off new nuclear-capable missiles.
The U.S. 2nd Infantry Division tweeted four photos on April 23 showing U.S. troops in protective suits equipped with gas masks, portable oxygen tanks and rifles conducting a search mission in a tunnel. One photo shows them guarding the entrance to the tunnel. The soldiers' chemical, biological and radiological protective gear is presumed to be new.
The drill was aimed either at searching for enemy leaders hiding in an underground bunker or seizing an underground command post and a nuclear missile facility.
The tweet did not specify the location, timing and purpose of the training but identified the personnel as "Ready First soldiers," i.e. members of the 1st Armored Brigade Combat Team. They were assigned to the 2nd Infantry Division on rotation.
"The North has fired intercontinental ballistic missiles and is also preparing more intensive provocations, including a fresh nuclear test," a South Korean military officer said, "The USFK's disclosure of the photos itself is a warning message to the North."