Sierra-class submarine

	A Sierra II submarine underway
Class overview
Name	Sierra class
Builders	Krasnoye Sormovo
Operators	Soviet Navy; Russian Navy;
Preceded by	Alfa class, Victor class
Succeeded by	Akula class
Built	1979–1992
In commission	1984–present
Planned	5
Completed	4
Canceled	1
Active	2
Laid up	2
General characteristics
Type	Nuclear attack submarine
Displacement	Sierra I:; 7,200 tons (surfaced); 8,300 tons (submerged); Sierra II:; 7,600 tons (surfaced); 9,100 tons (submerged);
Length	Sierra I: 107.16 m (351.6 ft); Sierra II: 110 m (360 ft);
Beam	Sierra I: 12.28 m (40.3 ft); Sierra II: 14.2 m (47 ft);
Draft	Sierra I: 8.8 m (29 ft); Sierra II: 8.8 m (29 ft);
Propulsion	Sierra I & II: 1 × PWR, 190 MW (HEU <= 45%); 2 × 1,002 hp (747 kW) emergency motors; 1 shaft, 2 spinners;
Speed	Sierra I & II: 10 knots (18.5 km/h) (surfaced); Sierra I: 34 knots (63.0 km/h) (submerged); Sierra II: 32 knots (59.3 km/h) (submerged);
Range	Effectively unlimited, except by food supplies
Complement	Sierra I & II: 61 & 72
Armament	Sierra I & II:; 4 × 650 mm (26 in) torpedo tubes (only Sierra I); 4 × 530 mm (21 in) torpedo tubes ( 6 x Sierra II); SS-N-21 Sampson SLCM; SS-N-15 Starfish anti-submarine weapon: 200 kt depth charge or 90 kg HE Type 40 torpedo; SS-N-16 Stallion, 200 kt depth charge or 90 kg HE Type 40 torpedo; Minelaying configuration: 42 mines instead of torpedoes;

The Sierra class (Soviet Project 945 Barrakuda and Project 945A Kondor; NATO reporting names Sierra I and Sierra II) are a series of nuclear-powered attack submarines built for the Soviet Navy and currently in service with the Russian Navy. The Sierra II boats are the only titanium-hulled submarines currently commissioned in the Russian Navy.

The Sierra class was a third generation Soviet attack submarine. It resembles the Alfa-class submarine in having a light and strong titanium pressure hull which enables the submarines of the class to dive to greater depths, reduce the level of radiated noise and increase resistance to torpedo attacks. It is powered by a single OK-650 pressurized water reactor. Due to the difficulties of working with titanium, and later also the fall of the Soviet Union, only two boats each of the Sierra I and Sierra II variants were made. The Akula-class submarine was created as an alternative to the Sierra class, being very similar but made of steel, and became much more numerous in the Soviet and Russian navies.

The upgraded version, the Sierra II class was specifically developed for search and destroy missions against United States Navy nuclear submarines. It has speeds and diving depth greater than its American counterparts at the time it was designed. It has also improved quieting and sonar. As of 2019 the Sierra I boats were in the reserve fleet, while the Sierra II boats were still active. In 2024 it was reported that the Sierra II submarines are docked at the Nerpa shipyard in Snezhnogorsk, Murmansk Oblast, and will undergo a modernization of their internal systems, though the refit had not started yet.