South Korea has successfully test-fired a modified version of the homegrown Korean Tactical Surface to Surface Missile-I (KTSSM-I), military sources said Friday, as the country is bolstering its defense capabilities against North Korea. The launch of the KTSSM-I variant, capable of being mounted on the homegrown Chunmoo multiple launch rocket system, took place Thursday at the Agency for Defense Development's testing site in Taean County, 109 kilometers southwest of Seoul, according to the sources. South Korea developed the KTSSM-I to secure precision strike capabilities against North Korean artillery pieces hidden in caves after the North's shelling of the South's northwestern border island of Yeonpyeong in 2010. The artillery shelling killed two civilians and two Marines. The missile is known to be able to penetrate the ground by a couple meters to reach underground targets. Source: Yonhap News Agency