According to Wikipedia: "This is the original Chinese version of Soviet P-15 Termit missile, and the first was SY-1, produced at Factory 320 (the Nanchang Aircraft Factory); Chinese sources identify the designers as Li Tongli and Lu Lin. The main difference between P-15 Termit and SY-1 missiles is that the unreliable aneroid altimeter of P-15 Termit was replaced by a much more reliable radar altimeter in SY-1. The successor of SY-1, designed by Peng Lisheng and designated as SY-1A, had a mono-pulse terminal guidance radar seeker replacing the original conical scanning radar seeker. The missile received a NATO reporting name CSS-N-1 Scrubbrush."