SOKS

SOKS, or System Obnarujenia Kilvaternovo Sleda, is a nonacoustic submarine detection system created by the Soviet Union. Various versions use detect radionuclides from the nuclear reactor in submarines, chemical signatures, and changes in the refractive index of water in the wake of submarines. It was first installed on the November-class K-14 submarine in 1969. SOKS was revealed in a document that was declassified in June 2017, written by the Central Intelligence Agency Directorate of Science & Technology.