The Kilo class is the NATO reporting name for a naval diesel-electric submarine that is made in Russia. The original version of the vessels were designated Project 877 Paltus (Turbot) in Russia. There is also a more advanced version, designated as Improved Kilo in the west, and Project 636 Varshavyanka in Russia. The Kilo will be succeeded by the Lada class submarine, which began sea trials in 2005.
The boats are mainly intended for anti-shipping and anti-submarine operations in relatively shallow waters. Original Project 877 boats are equipped with Rubikon MGK-400 sonar system (with NATO reporting name Shark Gill), which includes a mine detection and avoidance sonar MG-519 Arfa (with NATO reporting name Mouse Roar). Newer Project 636 boats are equipped with improved MGK-400EM, with MG-519 Afra also upgraded to MG-519EM. The improved sonar systems have reduced the number of operators needed by sharing the same console via automation.
Anechoic tiles are fitted on casings and fins to absorb the sonar sound waves of active sonar, which results in a reduction and distortion of the return signal. These tiles also help attenuate sounds that are emitted from the submarine, thus reducing the range by which the sub may be detected by passive sonar.