Kilo-class submarine

The Kilo-class submarines are a group of diesel-electric attack submarines designed by the Rubin Design Bureau in the Soviet Union in the 1970s and built originally for the Soviet Navy. Since it was introduced, more than 70 Kilo-class boats have been built, and around 60 were in active service as of 2023, not only in Russia but also in Algeria, Vietnam, India, Iran, Myanmar, and Poland. The first version had the Soviet designation Project 877 Paltus (Russian: Па́лтус, meaning "halibut"), NATO reporting name Kilo. They entered operational service in 1980 and continued being built until the mid-1990s, when production switched to the more advanced Project 636 Varshavyanka variant, also known in the West as the Improved Kilo class. The design was updated again by the Russian Navy in the mid-2010s to a variant called Project 636.3, also known as Improved Kilo II. Due to the delays and other problems with the successor Lada-class submarine, the Improved Kilo II has been built in larger numbers, with several more units under construction as of 2023.