Kilo-class submarine
The Kilo class, Soviet designation Project 877 "Paltus (, meaning "halibut"), NATO reporting name Kilo, is a class of diesel-electric attack submarines designed and built in the Soviet Union for the Soviet Navy. The class was built until the mid-1990s, when production was switched to the more advanced Project 636 "Varshavyanka (, meaning "Varsovian (inhabitant of Warsaw; feminine)") variant, also known as Improved Kilo class in the West. Role. These attack submarines 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 Arfa also upgraded to MG-519EM. MGK 400E can detect submarines with 0.05 Pa/Hz noisiness in 16 km and surface vessels with 10 Pa/Hz noisiness in 100 km. 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 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 at which the submarine may be detected by passive sonar. Future. The Kilo class was planned to have been succeeded by the . However, by November 2011 it was apparent that the Lada-class would be delayed because "Sankt Peterburg" (B-585), the lead boat of the class, had shown major deficiencies. On 27 July 2012, the Russian Navy commander-in-chief announced that construction of the Lada-class submarines would resume, having undergone design changes. Series production was reported  to be underway in the latter 2010s. Nevertheless, the Russian Navy also moved forward in the late 2010s, with the construction of Project 636.3, an improved version of the Kilo class. By November 2019, six units had been built for the Black Sea Fleet and further boats were planned for the Pacific and Baltic Fleets. Variants. One Kilo-class submarine, , was equipped with pump-jet propulsion. Operators. The first submarine entered service in the Soviet Navy in 1980, and the class remains in use with the Russian Navy today; 14 original Kilo-class vessels believed to still be in active  service with the Russian Navy, while eight Improved Kilo-class subs had been delivered as of 2021. About forty vessels have been exported to several countries: Specifications. There are several variants of the Kilo class. The information below is the smallest and largest number from the available information for all three variants of the ship. Project 636.3 units. Italics indicate estimates