Project 677 Lada-class.

Technical Data

• Armament

  The Project 677 Lada-class concentrates its principal offensive armament in six 533 mm bow torpedo tubes, which provide a common launch architecture for heavyweight torpedoes, submarine-launched missiles and naval mines. The most consistently cited Project 677 Lada-class configuration carries 18 weapons, allowing the weapon room to be configured according to mission rather than reserving separate launch systems for torpedoes and missiles. This is particularly significant given the submarine's smaller hull: Project 677 retains six 533 mm tubes and an 18-weapon nominal capacity despite reducing surfaced displacement to 1,765 t and crew to 35-36 compared with 2,350 t and 52 personnel for Project 636. The bow tubes are associated with an automated loading arrangement, consistent with the broader reduction in manual functions across the submarine. The available information does not establish that every submarine routinely carries all weapon types simultaneously, so the 18-weapon figure is better understood as total available magazine capacity rather than 18 torpedoes in addition to missiles.

  Torpedoes provide the submarine's primary close and medium-range anti-submarine and anti-surface attack capability, with weapons selected according to the intended target and mission. Armament includes at least three 533 mm torpedoes. The USET-80/USET-80K is an electric heavyweight torpedo with a range of 18 to 20 km and a maximum speed of 45 to 50 knots; the USET-80K includes the Keramika active/passive acoustic seeker for improved shallow-water and under-ice performance. The second, the SET-80, is an electric anti-submarine acoustic-homing torpedo with a range of 15 to 18 km and a maximum speed of 40 to 45 knots; it was developed as an intermediate Soviet anti-submarine weapon during late Cold War torpedo modernization. The third, the UGST Fizik-1/Physik, is a modern heavyweight torpedo combining a liquid-monopropellant axial-piston engine, a pump-jet propulsion, a fiber-optic wire guidance and a terminal acoustic homing to reach 25 km at a speed of 50 knots or 50 km at a speed of 40 knots. Because missiles and mines occupy weapon-storage capacity otherwise available to torpedoes, a strike-oriented or mine-warfare load would correspondingly reduce the number of heavyweight torpedoes available.

  Serial Project 677 submarines are associated with the Kalibr missile system, with the missiles fired horizontally through the existing 533 mm torpedo tubes. This arrangement gives the submarine missile capability without requiring a dedicated vertical launch section and allows the same six launch tubes to perform anti-submarine, anti-ship, and land-attack missions depending on the weapons loaded. This distinction is important because the export-oriented Project 1650 Amur concepts offer different missile arrangements, including proposed vertical launch cells. Those Amur configurations, subsequently, should not be transferred to the operational Russian Project 677 specification. For instance, the Kronshtadt is specifically associated with Kalibr capability, making tube-launched Kalibr-family weapons part of the corrected serial Lada configuration rather than merely an export proposal.

  The 3M54, part of the Kalibr/Club family and known by NATO as the SS-N-27 Sizzler, is a Russian anti-ship cruise missile that can be launched from submarines and surface ships, including through the Lada-class' 533 mm submarine torpedo tubes. It cruises at about Mach 0.8 at low altitude before accelerating to approximately Mach 2.9 during the final 20 km, reducing the time available for a target ship to react. The missile is 8.22 m long, weighs about 1,920 kg, and carries a 200 kg high-explosive warhead. Its export variants (3M-54E/3M-54TE) are capped at 220 km to 300 km to comply with export restrictions, while the 3M54M1 sacrifices the terminal supersonic sprint for greater payload and range efficiency, with a 450 kg warhead and a stated range of 300 km.

  Other weapons appearing in the available information include the RPK-6 Vodopad/SS-N-16 Stallion. This tube-launched anti-submarine rocket missile was designed to fire from standard 533 mm torpedo tubes, making it physically and electronically compatible with the Lada-class. Fired horizontally using compressed gas at depths down to 150 meters, this missile exits the water, ignites its solid-fuel rocket motor, and rises supersonically into the atmosphere at speeds of up to Mach 2.5. During its flight phase, the RPK-6 navigates via an inertial autopilot guidance toward the designated target coordinates at ranges between 35 and 50 km (approx. 19 to 27 nautical miles). Once over the target zone, the missile drops its payload (either a 400 mm UMGT-1/APR-3 lightweight acoustic homing torpedo or a low-yield nuclear depth charge) into the sea via parachute.

  Mine warfare is an explicit Project 677 mission, with mines carried in place of some or all of the normal torpedo and missile load. The available information in both Russian and English contains different maximum figures depending on the configuration, including 24 mines in one Lada-specific specification and 44 mines in a broader class description. It also identifies PM-1 and RM-2G mine types. These figures should not be combined with the normal 18-weapon load because mines can occupy different storage arrangements and multiple smaller mines can replace a smaller number of full-size torpedoes. The class can therefore be configured for offensive or defensive minelaying, but doing so likely changes the available torpedo and missile inventory rather than adding mines on top of a full combat load.

  A limited surfaced air defense capability is also available, with Igla-1M, Strela-3M and Verba man-portable surface-to-air missiles (MANPADS), with eight missiles carried in transport-launch containers. These weapons do not provide an underwater air defense capability and require personnel to employ them while the submarine is surfaced, making them a last-resort defensive weapon against helicopters or low-flying drones rather than an integral underwater missile system. Additionally, during sea trials in late 2024, photos emerged of the submarine Velikiye Luki (B-587) in the Baltic Sea fitted with a temporary deckhouse mount for a 12.7 mm Kord heavy machine gun to counter Ukraine's uncrewed surface vessels and kamikaze drones, but this should be treated as a standard equipment across the entire class.

• Design

  The Project 677 represents a substantial structural departure from the Project 877 and Project 636 Kilo-family submarines. The Project 677 was explicitly designed with a single-hull (mono-hull) configuration and a significantly smaller displacement than its predecessor, the Project 636 Kilo-class. This single-hull construction marked a major departure from traditional Soviet and Russian attack submarine design, which typically used double hulls, to make the vessel quieter, lighter, and more compact. The pressure hull is manufactured from AB-2 high-strength steel, maintains an almost constant diameter through much of its length, and terminates in approximately spherical bow and stern sections. Flat transverse bulkheads divide the pressure hull into five watertight compartments, while the internal arrangement is organized vertically across three levels. Streamlined light-hull structures cover portions of the pressure hull and contribute to the external hydrodynamic form. At the stern, each Project 677 submarine uses cruciform control surfaces, while the forward horizontal hydroplanes are mounted on the sail rather than immediately adjacent to the bow.

  The reduction in physical size compared with Project 636 is therefore substantial. The Project 677 possesses a 66.8 m waterline length and a 72 m overall length including outer casing and appendages, compared with 73.8 m for the Project 636, while maximum beam falls from 9.9 m to 7.1 m. Mean draught is 6.5 to 6.6 m, while surfaced displacement is 1,765 t, compared with 2,350 t for Project 636, a reduction of 585 t or 24.9%. The detailed Russian specifications place the Lada-class submerged displacement at 2,650 t, an increase of 885 t. The Project 677 Lada-class submarine is powered by two 1,250 kW diesel generators driven by Kolomna D49/ED-2 V8 diesel engines. These generators charge the onboard batteries, which drive a single permanent-magnet electric propulsion motor outputting around 2,700 kW. For silent docking and emergency maneuvering, the boat also relies on two auxiliary electric motors producing about 102 horsepower each.

  The Project 677's smaller pressure-hull volume is partly enabled by extensive automation. The normal complement is 35 to 36 personnel, compared with 52 sailors aboard a Project 636 submarine, reducing manpower by 16-17 personnel, or roughly one-third. The reduction affects more than personnel costs: fewer crew members require less accommodation volume, food and freshwater storage, sanitary capacity, life-support equipment, and working space during the submarine's stated 45-day endurance. This allowed Rubin to reduce the hull dimensions while retaining a six-tube weapon section, an 18-weapon nominal magazine, large sonar arrays, two battery groups, two diesel generators, and the electrical propulsion installation. Automation covers both combat functions through the Litiy automated combat information and control system, as well as technical functions through integrated machinery and submarine control systems.

  Acoustic signature reduction was one of the principal design objectives and affects the hull, machinery installation, and propulsion arrangement. The Project 677 uses the Molniya anti-sonar anechoic coating over its external surfaces. This treatment is intended both to reduce the strength of active-sonar energy reflected from the submarine and to attenuate some internally generated noise before it propagates into the surrounding water. Machinery and rotating equipment are mounted using vibration-isolation arrangements, including VI-type vibration isolators, limiting the transmission of structure-borne vibration into the pressure hull. The propulsion system uses one shaft and a seven-bladed skewed propeller, with the blade geometry intended to reduce pressure fluctuations, cavitation, and periodic propeller noise. Full electric propulsion also separates the diesel generators from direct mechanical propulsion of the shaft during normal operation, further supporting the class's acoustic reduction measures.

  The external geometry also reflects the requirements of the sonar installation. Each Lada-class submarine carries a large conformal or quasi-conformal acoustic array in the bow, supplemented by flank arrays and a low-frequency towed array. Moving the forward hydroplanes to the sail keeps large moving control surfaces and their associated hydrodynamic disturbances away from the bow sonar aperture. The relatively narrow beam, streamlined outer form, and single-shaft stern arrangement simultaneously reduce wetted area and hydrodynamic disturbance compared with the broader Project 636 hull. Russian claims state that Project 677 produces an acoustic field several times lower than earlier submarines, including a claim of noise levels more than three times lower than Project 636. No frequency-specific radiated-noise measurements in decibels are supplied, however, so this cannot be translated into a numerical detection range advantage.

  Survivability is based principally on underwater concealment, compartmentation and diving depth rather than armor. The five watertight compartments provide an internal subdivision intended to limit flooding following hull or system damage, while the AB-2 pressure hull supports a normal operational depth of 250 m and a maximum test depth of 300 m. The 50 m difference between operational and maximum/test depth provides a structural operating margin between routine diving and the deepest specified condition. The submarine's relatively compact dimensions and surfaced displacement were intended particularly for operations in coastal waters, internal seas and near-sea areas, although its endurance and snorkel range permit operations well beyond immediate coastal zones.

• Propulsion and performances

  The operational Project 677 Lada-class submarine uses a single-shaft diesel-electric propulsion combined with a full electric drive. The detailed serial configuration gives two Kolomna V8 D49/ED-2 diesel generators rated at 1,250 kW each, providing a combined generating capacity of 2,500 kW, together with two battery groups containing 120 cells each, for 240 cells in total. Propulsion is provided by a main all-mode electric motor rated at 4,050 to 5,500 hp, depending on the information, driving a single shaft and low-noise seven-bladed skewed propeller. Two 102 hp auxiliary electric motors provide additional low-power or reserve propulsion functions. This architecture differs fundamentally between surfaced or snorkeling power generation and submerged battery operation.

  The diesel generators produce electrical energy rather than providing the normal direct mechanical connection between diesel engines and the propeller shaft. Electrical output can supply onboard systems, recharge the batteries, and support propulsion through the electrical architecture, while the main electric motor provides the shaft power. When fully submerged without a snorkel, the diesel generators cannot operate because their internal combustion engines require atmospheric oxygen, so electrical energy is drawn from the battery installation. Each Project 677 can therefore operate without diesel combustion during battery-powered submerged movement, eliminating the need to expose a snorkel and removing diesel combustion and exhaust as immediate signatures. Once sufficient battery capacity has been consumed, however, the submarine must eventually return to snorkeling depth to operate the diesel generators and recharge unless it returns to port.

  The Project 677 Lada-class achieves an economical battery-powered submerged range of 650 nautical miles at 3 knots. Operating continuously at 3 knots, this corresponds mathematically to approximately 9 days of submerged travel, though true operational endurance varies depending on combat system usage, sensor draw, water conditions, and hotel loads. Secondary references citing a 7,500 nautical mile submerged range may actually refer to combined snorkeling/diesel operations rather than pure battery power. When operating on snorkel (diesel generator power at periscope depth), the boat achieves a cruising range of 6,500 nautical miles at 7 knots (approximately 12,038 km). Diving performance, for its part, is specified at 250 m operational depth and 300 m maximum/test depth.

  The submarine's maximum submerged speed is 21 knots (38.9 km/h), while its maximum surfaced speed is 10 knots (18.5 km/h). The top underwater speed of 21 knots represents a 2-knot increase over the preceding Project 636 Kilo-class despite the Lada's smaller displacement. However, running at maximum speed dramatically increases electrical draw, exhausting the battery pack in a fraction of the time compared to economical 3-knot cruising. Consequently, tactical operations rely on short bursts of high speed combined with extended periods of low-speed movement to preserve endurance and acoustic stealth. The submarine also has a stated 45-day overall endurance, which refers to the duration of a deployment supported by onboard fuel, provisions, freshwater, life-support capacity, and other consumables rather than uninterrupted battery-powered submergence.

  The development of an Air-Independent Propulsion (AIP) system, also referred to as an anaerobic propulsion system, for Russia’s Project 677 Lada-class submarines has been marked by long delays, technical challenges, and changing plans. Originally intended as a defining "fourth-generation" upgrade over the older Kilo-class to extend submerged endurance to around 45 days, the early Russian AIP design, based on electrochemical generators powered by hydrogen extracted from diesel fuel and oxygen, faced significant difficulties and failed to produce the required power during initial tests. Because of these failures and component supply disruptions following the dissolution of the Soviet Union, the submarines in the series (including the now-decommissioned lead boat Sankt Peterburg) were built or completed with conventional diesel-electric propulsion plants rather than AIP. Although shipyard officials indicated in 2019 that there were no immediate plans to equip active Lada-class hulls with AIP, research and development contract work resumed that same year to refine the fuel-cell generator technology for potential completion and integration into future production runs.

• Sensors and Onboard Equipment

  The Project 677 Lada-class introduced a substantially different underwater detection architecture from the Project 877 and Project 636 Kilo-classes, centered on the Lira integrated sonar complex. Rather than relying principally on a conventional bow array, the Lira combines a large quasi-conformal bow acoustic array, additional flank arrays, and a low-frequency towed array, giving the submarine several physically separated acoustic apertures. The bow array occupies a substantial portion of the forward hull and follows its contours, increasing the available acoustic aperture without requiring a conventional cylindrical arrangement of comparable internal volume. The flank arrays extend the passive listening baseline along the sides of the submarine, while the towed array can operate behind the hull at greater separation from machinery, propeller, and flow noise. Both passive and active acoustic functions are identified, including medium-frequency sonar components, while the low-frequency towed array is principally relevant to passive detection of comparatively weak or low-frequency signatures. No reliable numerical detection range against a defined submarine or surface target is supplied, so a fixed Lira detection range cannot be stated.

  The positioning of the sonar equipment directly influenced the submarine's hydrodynamic design. The Project 677 places its forward horizontal hydroplanes on the sail, keeping large moving control surfaces away from the bow acoustic array and reducing both physical obstruction and hydrodynamic interference in the sonar's forward sector. This differs from arrangements in which bow-mounted diving planes operate close to the principal acoustic aperture. The submarine's relatively narrow hull, vibration-isolated machinery, Molniya acoustic coating, and low-noise electric propulsion are also relevant to sensor performance because reducing self-generated noise improves the conditions under which passive sonar can detect weak external acoustic signatures. The seven-bladed skewed propeller and single-shaft arrangement similarly seek to limit propeller-generated noise that could mask contacts, particularly for the stern towed array. The Lada-class submarine's acoustic reduction measures therefore serve two purposes: making the submarine harder for an opponent to detect and lowering its own acoustic background for passive listening.

  The bow sonar array provides the principal forward acoustic coverage and supports the detection, classification, and tracking of submarines and surface vessels. Its quasi-conformal geometry allows a large acoustic aperture to be incorporated into the contours of the bow while leaving the submarine's six 533 mm torpedo tubes within the forward weapon section. The available information characterizes the Lira as capable of detecting particularly low-noise targets at long distances, but does not provide target type, sea state, water temperature profile, frequency, target aspect, or target radiated-noise level from which a meaningful numerical range could be calculated. Any single detection distance would therefore exceed the supplied information. What can be established is that the Lira is a multi-array system rather than a single acoustic sensor, combining different array positions and frequency regimes to improve detection coverage and provide information for the Litiy combat system.

  The flank sonar arrays increase the acoustic aperture available along the submarine's sides and supplement the forward array when contacts move outside its most favorable sectors. Large passive arrays can exploit the spatial separation of individual hydrophones to improve bearing determination and signal processing against low-level acoustic contacts. On the Project 677, their installation is particularly notable because the hull is only 7.1 m in beam, compared with 9.9 m for Project 636, requiring the sonar architecture to be integrated into a substantially narrower submarine. Information from the flank arrays can be correlated with the bow and towed arrays rather than treated as an independent tactical picture. This multi-aperture arrangement provides the combat system with acoustic information collected from different positions along and behind the hull, reducing the dependence on a single sensor geometry during submarine-versus-submarine engagements.

  At the stern, the Lada-class incorporates a low-frequency towed sonar array. Towing the receiving array behind the submarine separates its hydrophones from a significant proportion of hull machinery and hydrodynamic noise and creates a long acoustic baseline useful for passive surveillance. Low-frequency acoustic energy generally propagates farther through favorable underwater conditions than higher-frequency energy, making the array particularly relevant to long-range passive detection, although actual performance remains strongly dependent on oceanographic conditions and target signature. The towed array complements rather than replaces the bow and flank installations: the forward array remains important for target localization and active/passive operation, the flank arrays provide additional side-sector coverage, and the towed array provides a remote passive listening aperture.

  Above-water surveillance is provided principally by the Parus-98 integrated periscope complex, which includes an electro-optical observation capability rather than relying exclusively on a conventional hull-penetrating optical periscope. A non-hull-penetrating electro-optical/optronic mast allows imagery and sensor information collected above the surface to be transmitted electronically to operator positions inside the pressure hull. This arrangement removes the requirement for the operator to stand directly beneath an optical periscope tube and gives greater flexibility in locating observation and command stations within the control compartment. The Parus-98 is associated with observation, radar, and interception functions, supporting visual and electronic surveillance while the submarine operates at periscope depth. The mast can be exposed for shorter observation periods while the hull remains submerged, although the information provides no mast extension time, optical magnification, infrared detection range, or camera resolution from which more detailed quantitative performance could be established.

  The Project 677 also carries electronic support measures, radar-warning and direction-finding equipment, allowing it to detect electromagnetic emissions without necessarily transmitting with its own radar. Passive interception is particularly relevant at periscope depth because an active radar transmission can reveal the presence and potentially the position of a submarine to opposing forces. The direction-finding capability allows intercepted emissions to be associated with a bearing, while radar-warning functions can alert the crew to potentially hostile radar activity. These systems complement the submarine's acoustic sensors by providing a second category of passive information on surface ships, aircraft, and other emitters. As no detection ranges, frequency coverage, instantaneous bandwidth, or emitter-library capacity are provided for these systems, their capabilities should remain described by function rather than unsupported numerical values.

  Navigation is supported by an inertial navigation complex, which is particularly important because a submerged submarine cannot continuously obtain satellite navigation fixes. The system maintains estimates of the submarine's position, heading, and movement while it remains underwater and supplies navigation information to the command and weapon systems. Accurate navigation is required not only for safe underwater movement but also for employment of long-range tube-launched missile weapons, for which launch-point coordinates and submarine position must be known sufficiently accurately before firing. Periodic external fixes can correct the accumulated error inherent to inertial navigation when tactical conditions permit. The navigation complex was one of the systems modified on the redesigned serial submarines following experience with the Sankt Peterburg, making it part of the technical transition between the prototype and the Kronshtadt/Velikiye Luki configurations.

  Information from sonar, optronic, electronic surveillance, and navigation equipment is integrated through the Litiy automated combat information and control system. The Litiy combines sensor information, tactical processing, and weapon control functions, reducing the number of separate manual processes required to transform a detected contact into a tracked and potentially engageable target. This integration contributes directly to the reduction of the Project 677's crew to 35-36 personnel, compared with 52 aboard a Project 636. The system supports the submarine's six 533 mm torpedo tubes and associated torpedo and missile armament, allowing sensor tracks and navigation data to feed weapon employment. The Litiy was also among the technologically difficult elements of the original Project 677 program, with the lead Sankt Peterburg experiencing combat system problems alongside its propulsion and sonar deficiencies. The corrected serial configuration incorporated the results of those trials rather than reproducing the prototype's original system arrangement.

  Communications are handled through the Distantsiya integrated communications system, identified alongside the Lira, Litiy and Parus-98 as one of Project 677's principal new electronic systems. Its role is to integrate the submarine's communications functions while supporting the broader automated command architecture. The information does not provide a sufficiently detailed frequency breakdown, antenna inventory, satellite-communications specification, or underwater communications range to assign quantitative values to Distantsiya. The important configuration-level distinction is therefore the integration of communications, navigation, electronic surveillance, optronics and several sonar apertures into a common submarine architecture rather than treating each as an isolated installation. More than 130 new items of radio-electronic and shipboard equipment were associated with the Sankt Peterburg, helping explain both the technological ambition of the Project 677 and the integration difficulties encountered during the lead submarine's extended experimental operation.

The Project 677 Lada-class is intended to replace the Soviet-designed Project 877 and Project 636 Kilo submarines with a smaller, more automated, and acoustically quieter design.