CHINA used a top-secret SC-19 anti-satellite (ASAT) missile in a test last year against a target missile as part of a missile-defense system that remains shrouded in secrecy. The ASAT missile was fired against a new medium-range missile and details were disclosed in a State Department cable made public recently by WikiLeaks that included an outline of a diplomatic protest note to Beijing about both Chinese weapons programs. The cable provides the first detailed U.S. assessment of what defense officials say is a major strategic advancement in China’s military buildup. It reveals that China’s anti-satellite system was developed for use...