The Improved Kilo II-class submarine (Project 636.3 Varshavyanka) is a modernized variant of the Soviet-designed Kilo-class diesel-electric attack submarine, developed for the Russian Navy. Known for its stealth, endurance, and advanced sensor capabilities, it is often referred to as a “black hole” due to its exceptionally low acoustic signature.Armed with Kalibr (SS-N-27/SS-N-30) cruise missiles, 533mm torpedoes, and mines, the Improved Kilo II is capable of striking land, sea, and underwater targets with high precision. It features upgraded sonar, improved battery capacity, and an advanced combat system, allowing for greater situational awareness and combat effectiveness.With a top speed of 20 knots submerged, a range of 7,500 nautical miles, and the ability to remain submerged for extended periods using air-independent operations (AIP) alternatives, the 636.3 serves as a key component of Russia’s coastal defense and strategic deterrence. Several units have been deployed in the Black Sea, Pacific, and Baltic Fleets, as well as exported to China, Algeria, and Vietnam.