The Kilo-class submarines are a group of diesel-electric attack submarines designed by the Rubin Design Bureau^[1][2][3] in the Soviet Union in the 1970s and built originally for the Soviet Navy.

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 (Russian: Варшавянка, after the revolutionary song of the same title) variant, also known in the West as the Improved Kilo class.^{[citation needed]} 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.

The Project 877 attack submarines were 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 (9.9 mi) and surface vessels with 10 Pa/Hz noisiness in 100 km (62 mi).^[4] 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.^[5] 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.^[6]

Project 636 and 636.3 submarines can launch Kalibr (and their Club export version) cruise missiles. It was reported in September 2022 that they can carry four Kalibr missiles, and can launch them through two of their six torpedo tubes.^[7]

A single Project 877 submarine, B-871 Alrosa, is equipped with pump-jet propulsion, instead of a propeller.^[8] It has been retrofitted for the Kalibr missile.^[9]

It was planned for Project 636 (Improved Kilo) to be succeeded by the Lada class in Russian Navy service. 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.^{[citation needed]} Series production was reported to be underway in the latter 2010s.^{[10][needs update]}

The Russian Navy also moved forward in the late 2010s, with the construction of Project 636.3, also known as Improved Kilo II. The first-in-class was named Petropavlovsk-Kamchatsky (PPK) and was launched by the head of Admiralty Shipyard Alexander Buzakov on 28 March 2019, or some thirty months after commission.^[1] By November 2019, six units had been built for the Black Sea Fleet and further boats were proposed, but not funded, for the Pacific and Baltic Fleets.^[3]

In June 2022, an unconfirmed report from within Russia's defense industry suggested that a further tranche of six additional Project 636.3 vessels might be ordered to start construction in around 2024.^[11] The PPK class "is slightly longer in length — the sub's submerged displacement is around 4,000 tons — and features improved engines, an improved combat system, as well as new noise reduction technology; it can fire both torpedoes and cruise missiles, launched from one of six 533-millimeter torpedo tubes."^[1] The PPK class has a seven-bladed propeller, instead of the six-bladed propeller of the Project 877 class.^[9]

There are several variants of the Kilo class. The information below is the smallest and largest number from the available information for all three main variants of the boat.^[12]

• Displacement:
  • 2,300–2,350 tons surfaced
  • 3,000–4,000 tons submerged
• Dimensions:
  • Length: 70–74 meters
  • Beam: 9.9 meters
  • Draft: 6.2–6.5 meters
• Maximum speed
  • 10–12 knots surfaced (18–22 km/h)
  • 17–25 knots submerged (31–46 km/h)
• Propulsion: Diesel-electric 5,900 shp (4,400 kW)
• Maximum depth: 300 meters (240–250 meters operational)
• Endurance
  • 400 nautical miles (700 km) at 3 knots (6 km/h) submerged
  • 6,000 nautical miles (11,000 km) at 7 knots (13 km/h) snorkeling (7,500 miles for the Improved Kilo class)
  • 45 days sea endurance
• Armament
  • Air defence: 8 Strela-3 or 8 Igla-1, but after sea trial it^[which?] was rejected by the navy.^{[citation needed]}
  • Six 533 mm torpedo tubes with 18 53-65 ASuW or TEST 71/76 ASW torpedoes or VA-111 Shkval supercavitating torpedoes, or 24 DM-1 mines,
• Crew: 52
• Price per unit is US$200–250 million (China paid about US$1.5–2 billion for 8 Project 636 Kilo-class submarines)^{[when?][citation needed]}

In 2015 five Kilo-class submarines were deployed to the Russian naval facility in Tartus, Syria. At least two of the units reportedly attacked land targets inside Syria with 3M54 Kalibr cruise missiles (NATO designation: SS-N-27A "Sizzler").^[3] On 8 December 2015 marked the first time a Kilo-class submarine fired cruise missiles against an enemy. The B-237 Rostov-on-Don struck two targets near the ISIS capital of Raqqa by the missile attack.^[13] The B-237 transited the Dardanelles on its way back to the Black Sea on 12 February 2022.^[14]

The B-871 Alrosa a pump-jet Kilo class, which derives from the Project 877 hull, participated in the Russo-Ukraine War.

After the sinking of the Russian cruiser Moskva in April 2022, it was remarked that the Kilo-class subs were the only members of the Black Sea Fleet whose orders did not prohibit venturing into Ukrainian waters near Odessa during the Russian invasion of Ukraine.^[15] In September 2022, after the early 2022 Crimea attacks, the UK MoD said that the Kilo-class submarines were moved from Sevastopol to the Port of Novorossiysk in Krasnodar Krai.^[16][7]

On 13 September 2023, B-237 Rostov-on-Don was severely damaged by a Ukrainian Storm Shadow missile strike while it was drydocked in Sevastopol.^[17][18][19]

The first submarine entered service in the Soviet Navy in 1980, and the class remains in use with the Russian Navy today; around 11 original Kilo-class vessels believed to still be in active service with the Russian Navy (as of 2023), while new Improved Kilo–class subs are being delivered through the 2020s to replace them. About forty vessels have been exported to several countries:

•  Algeria: 2 original Kilo (Project 877), 4 Improved Kilo (Project 636).^{[20][21][22][23][24][25]}
•  People's Republic of China: 2 original Kilo (Project 877), 10 Improved Kilo (Project 636).^[26][27]
•  India: 10 original Kilo (Project 877), 1 sustained major casualty^[12][28] – designated as the Sindhughosh class
•  Myanmar: one boat transferred from Indian Navy by March 2020.^[29][30]
•  Poland: 1 original Kilo (Project 877) – ORP Orzeł.^[31][32]
•  Iran: 3 original Kilo (Project 877).^[27]
•  Romania: 1 original Kilo (Project 877) – Romanian submarine Delfinul (not operational).^{[citation needed]}
•  Russia: 10–11 original Kilo (Project 877), 11 Improved Kilo (Project 636.3)^[33] and 1 additional Improved Kilo on order (636.3) for Pacific Fleet to be delivered in 2024.^[34] One further Improved Kilo ordered in August 2020, during the International Military-Technical Forum "ARMY-2020";^[35][36] up to six additional boats of the class intended to replace Project 877 units; first three ordered in 2023.^[37]
•  Vietnam: 6 Improved Kilo (Project 636)^[38][39][40] – Hồ Chí Minh City, Hà Nội, Hải Phòng, Đà Nẵng, Khánh Hoà, Bà Rịa-Vũng Tàu.

• The Polish Kilo-class submarine ORP Orzeł, 26 June 2011
• Russian Kilo-class submarines in Polyarny, Murmansk Oblast
• An Algerian Kilo-class submarine
• A Chinese Kilo-class submarine being delivered from Russia as deck cargo in 1995.
• ORP Orzeł, the control room of an 877E-class submarine
• The Iranian Kilo-class submarine Yunes, during delivery in 1995.
• Indian Kilo-class submarine, INS Sindhughosh
• Diesel submarine Kilo-class Kaluga returns from a long voyage
• Russian Improved Kilo-class submarine Ufa during the Russian Navy Day parade in 2023.

• List of Soviet and Russian submarine classes
• List of submarine classes in service
• Future of the Russian Navy
• Cruise missile submarine
• Attack submarine