System Defense Command (SDC) was a division of the Grayson Space Navy. Its was charged with maintaining the long-range detection arrays, border sensors, and several squadrons of quick reaction forces to identify and respond to possible threats to the Yeltsin's Star System. It was also in charge of fixed defenses such as orbital fortresses, missile pods and planetary defense systems. Its commanding officer in the early 1920s PD was Admiral Leon Garret. (Companion)