Kilo class, Soviet designation Project 877 Paltus (Russian: Па́лтус, 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 variant, also known as Improved Kilo-class by the West