U.S. Forces Korea (USFK) has revealed its recent training at an underground facility in an apparent show of its stepped-up efforts to ensure defense readiness following North Korea‘s recent missile launches.

In a recent Twitter post, the USFK’s 2nd Infantry Division disclosed a series of photos showing troops wearing gas masks and protective suits during a specialized training program. It did not reveal where and when the training occurred.

“Ready First Soldiers conducted training at the underground facility,” the unit wrote on Twitter.

Ready First soldiers refer to those belonging to the 1st Armored Brigade Combat Team, 1st Armored Division. (Yonhap)