Passage: The Dong Feng 4 (Chinese: 东风-4; pinyin: Dōng Fēng Sì; literally: 'East Wind 4') or DF-4 (also known as the CSS-3) is a two-stage Chinese Intercontinental ballistic missile with liquid fuel (Nitric acid/Unsymmetrical dimethylhydrazine).  It was thought to be deployed in limited numbers in underground silos beginning in the 1970s and early 1980s.  The Dong Feng 4 has a takeoff thrust of 1,224.00 kN, a takeoff weight of 82000 kg, a diameter of 2.25 m, a length of 28.05 m and a fin span of 2.74 m.  The range of the Dong Feng 4, which is equipped with a 2,190 kg nuclear warhead with 3.3 Megaton yield, with a nominal range of 5,500 km.  This gives it sufficient range to strike targets as far away as Russia, India, and American bases in the Pacific. The missile uses an inertial guidance system, resulting in a large CEP of 1,500 meters.  As of 2017, 10-15 launchers are deployed.

Question: What kind of system does the missile use?
an inertial guidance system