The Sky Spear (天戟 Tien Chi) is a Taiwanese short-range ballistic missile (SRBM) capable of striking targets on mainland China. Derived from the Sky Bow II (Tien Kung-2) surface-to-air missile, the Tien Chi has a two-stage booster that extends over the single-stage Tien Kung-2. The Sky Spear was developed by the Chungshan Institute of Science and Technology (CSIST) in Taiwan. As of early 2001, up to 50 Tien Chi missiles were deployed at two sites: Tungyin Island, and an unidentified second location. The Tungyin Island missiles are said to be housed in silos and protected by batteries of Tien Kung-2 SAMs.