Russia's secret Poseidon nuclear submarine Khabarovsk begins sea trials in White Sea.

On August 17, 2026, the Russian Navy's Project 09851 Khabarovsk nuclear submarine departed the Sevmash shipyard in Severodvinsk to commence its first factory sea trials in the White Sea. This deployment initiates the critical at-sea testing phase for the first submarine designed from its inception to carry six 2M39 Poseidon nuclear-powered, intercontinental autonomous underwater vehicles. The trials will evaluate the 10,000-tonne vessel's novel forward-hull geometry, integrated propulsion systems, and overall structural integrity prior to state acceptance and its anticipated transfer to the Pacific Fleet.

Measuring approximately 135 meters in length with a displacement of 10,000 tonnes, the Khabarovsk is structurally optimized around two longitudinal hangars engineered to accommodate six 2P39 launch installations. Following a highly delayed construction timeline dating back to 2014, these factory trials will comprehensively test its KTP-6-185SP pressurized-water reactor, pump-jet propulsion, and diving behavior to ensure technical readiness for deploying up to 660 tonnes of specialized strategic underwater payload.

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The Khabarovsk is the first Russian nuclear-powered submarine built specifically to carry and launch six long-range, nuclear-powered Poseidon underwater weapons against strategic targets. (Picture source: X/Massimo Frantarelli)

On August 17, 2026, Massimo Frantarelli revealed that Russia's Project 09851 Khabarovsk nuclear submarine departed Severodvinsk for its first factory sea trials in the White Sea, opening the at-sea test phase for the first submarine designed from the keel up to carry six 2M39 Poseidon nuclear-powered underwater weapons. The milestone came exactly 4,404 days after construction began on July 27, 2014, and more than 14 years after Rubin Central Design Bureau received the design contract from the Russian Ministry of Defence on June 19, 2012. The original contract called for delivery in 2020, putting the program roughly six years behind that target when the Khabarovsk finally reached sea trials.

The submarine was rolled out of Sevmash workshop No. 50 on November 1, 2025, and physically lowered into the water around November 30, leaving roughly 8.5 months for completion afloat, mooring trials, reactor and propulsion preparation, electrical integration, navigation system checks, and preparations for operation away from the shipyard. Factory trials must now establish machinery performance, steering response, diving behavior, propulsion reliability, and operation of the integrated onboard systems before state acceptance trials can begin. The Khabarovsk is also materially different from the BS-329 Belgorod, commissioned on July 8, 2022, because the Belgorod was reconstructed from an unfinished Project 949A hull whereas Project 09851 was dimensioned around Poseidon from inception.

The current configuration assigns six 2P39 launch installations to Khabarovsk, compared with four on Belgorod, a 50% increase in embarked Poseidons. After acceptance, the Khabarovsk is intended for the Pacific Fleet and Kamchatka, where Krasheninnikov Bay is being prepared to support Project 09851 and 09852 submarines and their Project 20183 support ship. Confirmed information about the submarine is scarce; for instance, measurements following the November 2025 rollout place the Khabarovsk at roughly 135 m long and 13.5 m in beam, with another measurement giving 135 to 140 m, substantially refining earlier estimates of 113 to 120 m made before the complete hull could be measured.

One reconstruction calculated a main pressure hull diameter near 13 m and a maximum width of roughly 16 m across the enlarged forward section, dimensions consistent with accommodating longitudinal Poseidon compartments beside the central pressure structure. Displacement is repeatedly placed near 10,000 tonnes. For comparison, a 2021 reconstruction put Project 09851 at roughly 120 m against about 160 m for Project 955 Borei, with most of the difference resulting from deletion of the Borei's ballistic missile compartment behind the sail. The Borei carries 16 RSM-56 Bulava SLBMs in that section, whereas the Khabarovsk has no equivalent vertical missile block. Project 09851 is also considerably shorter than the 184-m, roughly 30,000-tonne Belgorod because it eliminates the converted submarine's large central special mission section used to support deep-diving vehicles.

The stern, pump-jet area, and rudder arrangement visible after rollout are very close to Project 955A Borei-A, while the forward section follows the basic geometry required for Poseidon carriage. In practical terms, the design combines an established large submarine propulsion section with a new weapons bow and deletes the large central payload sections found on both Borei and Belgorod. This is why the Khabarovsk should not be treated as another Russian SSN or SSGN: its 10,000-tonne hull is optimized primarily to move six exceptionally large strategic weapons to their launch area. One machinery configuration associated with Project 09851 uses a KTP-6-185SP pressurized-water reactor with roughly 200 MW of thermal power and a turbine developing roughly 50,000 hp, although an OK-650V-family reactor has also been associated with the Borei-derived stern.

The propulsion train uses one shaft and a pump-jet rather than a conventional exposed multi-bladed propeller, while two auxiliary maneuvering thrusters provide low-speed control during docking and confined-water operations. Maximum submerged speed is set at 30 to 32 knots, or 56 to 59 km/h. At 30 knots, the Khabarovsk would cover 1,000 nautical miles in 33.3 hours if it could sustain maximum speed, although an operational transit would normally be slower because acoustic discretion rather than maximum speed is central to submarine survivability. Maximum or normal operating depth is generally placed near 500 m, draft near 10 m, crew near 100, and patrol endurance at 90 to 120 days. The endurance figure gives a 30-day spread between the lower and upper estimates and permits multi-month deployments without the submarine's nuclear propulsion being the limiting factor, since food, crew endurance, and consumables become more restrictive than reactor fuel.

The Poseidon itself is associated with depths as great as 1,000 m, meaning the weapon could descend roughly 500 m below the carrier's estimated operating envelope after launch. The distinction between the two operating envelopes is important: the Khabarovsk does not have to reproduce Poseidon's claimed depth or endurance because its function is to survive the crewed patrol, reach a suitable release area, and launch the vehicles, after which their independent nuclear propulsion assumes the long-distance transit. The forward half of the submarine contains the principal engineering trade-off behind the entire Project 09851 design. The Khabarovsk is configured for six 2P39 launchers, with the six Poseidons most plausibly divided between two flooded longitudinal hangars positioned along the port and starboard sides of the bow. Large forward doors provide loading and launch paths, while the conventional torpedo compartment occupies the much narrower space between the two Poseidon sections.

The arrangement accounts for the unusual width of the bow and has similarities to older Soviet submarines that placed oversized cruise missiles alongside the central pressure hull rather than inside a conventional torpedo room. A double-bubble or divided pressure hull geometry has also been associated with the forward section as a means of recovering internal volume between the two large weapons compartments. The dimensional problem is substantial: a Poseidon is most commonly placed near 20 m long and 1.8 to 2.0 m in diameter, while the wider range of estimates extends from 16 to 24 m long and 1.5 to 2.0 m in diameter. Mass estimates extend from roughly 55 tonnes through 100 tonnes to about 110 tonnes per vehicle. Six 55-tonne vehicles would weigh 330 tonnes; six at 100 tonnes would reach 600 tonnes; and six at 110 tonnes would total 660 tonnes. Those figures exclude the mass of the 2P39 launch installations, support equipment, structural reinforcement, doors and flooding systems.

Using the 20-m length figure, six weapons laid longitudinally represent a payload whose individual vehicles are roughly 15 times the length of a standard 533 mm torpedo's diameter and whose combined mass can exceed that of several complete small conventional submarines. The Poseidon trades the speed of a ballistic weapon for an underwater route and a much longer autonomous transit. Its nuclear propulsion unit is associated with a range near 10,000 km, or 6,200 miles, and a frequently cited maximum operating depth of 1,000 m. Speeds most consistently associated with the vehicle are 60 to 70 knots, equivalent to 111 to 130 km/h, while a 100 knots, or 185 km/h, figure has also circulated without the same level of consistency. These numbers allow the delivery timeline to be quantified. At 60 knots, 1,000 km requires nine hours, 5,000 km requires 45 hours, and 10,000 km requires 90 hours.

At 70 knots, the same distances require 7.7, 38.6, and 77.2 hours. Even a 100-knot transit would require about 54 hours to cover 10,000 km. The Poseidon consequently cannot perform the same prompt strategic function as a Bulava SLBM, whose flight time against intercontinental targets is measured in tens of minutes. Its characteristics instead favor geographically fixed targets whose coordinates remain relevant after one to four days of underwater travel, particularly ports, naval bases, coastal military installations, industrial infrastructure and population centers. Large naval formations are also included among potential target categories, but a moving formation introduces a substantially more demanding terminal search and guidance problem after a transit potentially lasting several days. Warhead figures are even less stable than the speed estimates: values up to 2 megatons coexist with estimates of 20 to 25 megatons, while other historical figures extend still higher. 

The price paid for carrying six such vehicles is visible in the Khabarovsk's conventional armament. One configuration assigns six to eight 533 mm tubes to the central bow compartment between the Poseidon hangars, with USET-80, Fizik-2 and Futlyar heavyweight torpedoes, Kalibr missiles and naval mines among the weapons associated with those tubes. The number of reloads is not established, which prevents a reliable total conventional ammunition figure, but the geometry makes one limitation clear: a conventional Russian SSN can allocate much of its bow to torpedo tubes, handling machinery, and horizontal storage racks, whereas the Khabarovsk gives most of the corresponding volume to two Poseidon hangars. The conventional weapons section is therefore secondary by design due to displacement constraints.

A Yasen multipurpose submarine can use its weapons inventory for anti-submarine warfare, anti-surface warfare, and long-range land attack, while the Khabarovsk's six principal weapons are strategic systems with transit times potentially exceeding three days over intercontinental distances. The 533 mm battery consequently provides the boat with a means to engage submarines or surface ships, lay mines, and potentially launch Kalibr weapons without converting Project 09851 into a general-purpose attack submarine. Igla and Verba MANPADS have additionally been associated with the boat, but these can only provide highly restricted short-range protection when the submarine is surfaced and have no relevance during submerged operations. However, if the Poseidon cannot be fielded in usable numbers, the Khabarovsk cannot recover the lost strategic capacity by carrying 16 SLBMs like a Borei or the much larger conventional missile and torpedo inventory of a Yasen-M. 

The Belgorod submarine further illustrates both the infrastructure Russia already possesses and the limitations that the Khabarovsk was designed to remove. BS-329 began construction in 1990 as a Project 949A Oscar II cruise-missile submarine, was formally laid down on July 24, 1992, and reached roughly 76% completion before work on its original configuration stopped in 2006. Reconstruction under Project 09852 began in 2012, retaining the large Project 949A-derived hull while incorporating Poseidon equipment and facilities for deep-diving submersibles. The Belgorod eventually began factory sea trials on June 21, 2021, and entered service on July 8, 2022, meaning more than 30 years separated its formal keel-laying from commissioning. Its dimensions are correspondingly exceptional: roughly 184 m long, 15 m in beam and 30,000 tonnes submerged, compared with roughly 135 m, 13.5 m and 10,000 tonnes for the Khabarovsk.

The current configuration attributes four 2P39 launchers to Belgorod and six to Khabarovsk, although earlier information assigned six to Belgorod as well, so the exact Project 09852 load remains one of the unresolved numerical discrepancies. The later four-round figure would mean Khabarovsk carries two additional vehicles despite being roughly 49 m shorter and only one-third of Belgorod's submerged displacement, because it eliminates the large special-mission section and devotes more of its usable volume specifically to Poseidon. Weapon development also moved closer to carrier development on October 28, 2025, when Russia reportedly conducted a Poseidon test in which the vehicle was launched from a submarine and its onboard nuclear power unit was activated.

The Khabarovsk entered the water roughly one month later and began sea trials less than ten months after that test, so Russia is now testing the dedicated carrier while the weapon itself remains in a comparatively recent phase of nuclear-propulsion validation. The resulting force remains numerically limited despite more ambitious plans attached to the program. As of August 18, 2026, Russia possesses one commissioned Poseidon carrier, the Belgorod, and one purpose-built carrier undergoing factory trials, the Khabarovsk; there is not yet an operational flotilla of serial Project 09851/09853 boats. The Khabarovsk is intended for the Pacific Fleet, and Krasheninnikov Bay on Kamchatka is being prepared with dedicated facilities for Projects 09851 and 09852 together with a Project 20183 support ship, showing that the force requires specialized shore handling in addition to the carrier submarines themselves.

Force plans also remain inconsistent. One version calls for four carriers divided evenly between the Northern and Pacific fleets, another calls for five Poseidon-armed submarines, and another places the broader Project 09851/09853 production run at three or four boats. Project 09853 is intended as a serial or modified follow-on to Khabarovsk, with Orenburg associated with a possible unit and autumn 2025 preparations, but no confirmed construction start is established in 2026. The Ulyanovsk is also repeatedly associated with another Poseidon carrier and a 2017 keel-laying, although that creates a project-number and naming conflict with the Project 08851 Yasen-M submarine Ulyanovsk laid down in 2017.

The distinction between the confirmed and planned force is therefore important: Russia has one converted carrier in service, one dedicated six-launcher carrier at the beginning of sea trials, specialized Pacific support infrastructure under development, and several competing plans for subsequent hulls. The immediate significance of the August 17 trial is narrower but still measurable: for the first time Russia has taken to sea a roughly 135-m, 10,000-tonne submarine whose bow, internal volume and weapons architecture were built specifically to deploy six intercontinental nuclear-powered Poseidons, moving the program from dependence on the converted Belgorod toward testing the configuration on which any larger operational Poseidon force would have to be based.

Written by Jérôme Brahy

Jérôme Brahy is a defense analyst and documentalist at Army Recognition. He specializes in naval modernization, aviation, drones, armored vehicles, and artillery, with a focus on strategic developments in the United States, China, Ukraine, Russia, Türkiye, and Belgium. His analyses go beyond the facts, providing context, identifying key actors, and explaining why defense news matters on a global scale.

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