Poseidon: The Ultimate Weapon of Vengeance [i]

"To wipe out the enemy coast..."

A weapon system on its own

The Poseidon, designated 2M39 in Russian service and known to NATO as Kanyon, is among the most enigmatic and controversial strategic systems developed in recent years. It resists conventional classification: neither a conventional torpedo nor a crewed submarine, it represents a novel class of autonomous, nuclear-powered underwater vehicle designed to carry a nuclear warhead.

This autonomous, nuclear-powered underwater vehicle, formerly designated Status-6, has been described in open sources as capable of carrying a very large thermonuclear warhead (some reports even cite yields as high as 100 megatons)¹ and of transiting intercontinental distances at depths that would place it beyond the reach of most conventional antisubmarine weapons, arguably leaving only exceptionally large-yield nuclear depth charges as a theoretical counter. Open reporting also suggests it can adopt multiple mission modes: a high-speed transit phase at depth, which offers rapid repositioning but is more readily detectable by advanced acoustic sensors, and a prolonged low-speed, low-observability cruise that exploits nuclear endurance to remain submerged for effectively indefinite periods before conducting a final approach to a target.

As with many novel Russian weapons, most technical details remain classified; nevertheless, a synthesis of open-source analysis and official Russian statements permits a broad—albeit uncertain—reconstruction of Poseidon’s design philosophy, capabilities, and potential strategic effects.

The system’s existence has been publicly acknowledged by Russian officials and illustrated in state imagery since 2015, with subsequent references appearing in speeches by President Vladimir Putin. Official portrayals consistently show a large, torpedo-like unmanned vehicle propelled by a compact nuclear powerplant. Independent Western analysts and think tanks, including the Bulletin of the Atomic Scientists, the Hertie School, and GlobalSecurity.org, generally assess that the platform is powered by a compact liquid-metal-cooled fast reactor (most plausibly lead–bismuth), measures roughly 18-24 meters in length with a diameter near two meters, and is intended to operate at depths on the order of one kilometer or more. Open estimates for warhead yield typically cluster around two megatons, although some Russian statements and more sensational sources have suggested far larger figures; taken at face value, those Russian claims imply yields on the order of 100 megatons - roughly fifty times the commonly cited Western estimate - underscoring the large and unresolved discrepancy between official Russian messaging and independent technical appraisals.

To illustrate the size of Poseidon, the following picture helps:

The Reactor

Let’s now dive into the design: the rationale for nuclear propulsion in a torpedo-sized system is straightforward. A platform designed to cross oceans autonomously, remain submerged for long durations, and maintain high speed cannot rely on chemical fuel or battery power. Only a nuclear reactor provides the energy density required to sustain such endurance and performance. Among reactor options, liquid-metal-cooled fast reactors are the most plausible because of their compactness and high power density. Russia has extensive historical experience with this technology, particularly in the Project 705 & 705K Alfa-class submarines, which used lead–bismuth–cooled VT-1 reactors (see the illustration below). These reactors can achieve high thermal power in small volumes and operate without bulky high-pressure systems, making them suitable for integration into a limited-diameter hull. Although pressurized water reactors are technically simpler and widely used in naval propulsion (submarines, aircraft carriers, and icebreakers), their volume, shielding requirements, and mechanical complexity make them less ideal for such a compact, high-speed vehicle. Liquid-metal reactors are not without drawbacks, as they require careful temperature management to avoid coolant solidification and create radiological hazards through polonium formation, but their advantages in power density likely outweigh these issues for a weaponized, non-recoverable platform.

Project 705 (705K) top and liquid-metal cooled nuclear reactor functional schematics.

Assuming a reactor output in the range of several to a few tens of megawatts, Poseidon’s claimed speed envelope becomes theoretically plausible. Hydrodynamic drag increases rapidly with speed, so propelling a large underwater body beyond fifty knots demands immense power. Achieving 100 knots would require advanced, cavitation-resistant designs and a propulsion system of extraordinary efficiency. The operational depth of about one kilometer is within Russia’s known capabilities, as shown by deep-diving submarines and titanium-hulled submersibles already in service. However, it implies a robust and pressure-resistant hull structure.

The well-known and the utterly unknown converge in the story of Poseidon’s propulsion ²,³,⁴,⁵,⁶. To understand where it came from, one must first examine the history of small liquid-metal nuclear propulsion in the Soviet Union and Russia, a field that combined extraordinary ambition, advanced engineering, and high-risk experimentation. Beginning in the late 1950s, Soviet scientists and engineers pursued compact reactors cooled with liquid metals, aiming to produce energy-dense, high-power systems for applications where conventional reactors could not fit—primarily submarines, specialized naval vessels, and later, experimental space systems.

Liquid metals such as sodium, sodium–potassium alloys, and lead–bismuth eutectic offered unique advantages: high thermal conductivity, low vapor pressure, and the ability to operate at very high temperatures without pressurization. These properties enabled smaller cores capable of producing significant power, essential for high-speed submarines or autonomous underwater vehicles, and for space reactors requiring long-term, reliable electricity. The development of such reactors was not confined to a single laboratory; it involved a network of Soviet research institutes and design bureaus, including the Kurchatov Institute, the Institute for Physics and Power Engineering (IPPE) in Obninsk, OKBM Afrikantov in Nizhniy Novgorod, Gidropress, and the Luch and Krasnaya Zvezda organizations responsible for thermionic conversion and reactor assembly.

One of the most striking applications of this technology was in the Project 705 “Alfa” submarines. These boats required extremely high speeds in small hulls, and engineers met this demand with lead-bismuth-cooled reactors such as the BM-40A and OK-550. The liquid-metal coolant allowed cores to deliver immense power without the size and weight penalties of conventional systems. Yet these advantages came with severe challenges: lead–bismuth solidifies at relatively modest temperatures, so a loss of heat could freeze the reactor, and handling the radioactive coolant and highly enriched fuel required specialized shore infrastructure. These operational difficulties limited the number of vessels that could benefit from this technology. Still, the lessons learned provided critical experience in coolant chemistry, materials science, and reactor maintenance under extreme conditions.

To illustrate the complexity, the following is an example of one liquid metal piping from the Project 705 submarine:

Results of cleaning and corrosion testing: Left: before cleaning; right: after cleaning (Hydrogen cleaning of the pump test loop pipeline in 1980). No corrosion observed on EP-823Sh steel (fuel element cladding) after testing in lead-bismuth coolant (LBC) at 600 °C for 50,000 hours. There has been no equipment failure or accident on any reactor installation caused by corrosion of steels in lead-bismuth coolant. Furthermore, no accidents or failures attributable to slag deposits have occurred since hydrogen cleaning was implemented.

In parallel, Soviet engineers explored liquid-metal reactors for space applications, producing the TOPAZ series of thermionic power reactors. These reactors used liquid metal, often sodium–potassium alloys, to remove heat from the fuel while directly converting thermal energy to electricity through thermionic elements integrated into the core. The reactors were compact, robust, and capable of providing continuous electrical power for years, making them ideal for satellites and other long-duration space missions. TOPAZ reactors were later acquired by Western researchers after the collapse of the Soviet Union, offering a rare glimpse into advanced Soviet nuclear space technology.

The broader development of sodium-cooled fast reactors for civilian power, such as the BN series, including BN-350, BN-600, and BN-800, demonstrates the Soviet mastery of liquid-metal technology beyond niche applications. While these reactors were much larger than those used in submarines or spacecraft, they shared many technological principles, particularly the use of liquid metal to manage heat transfer in a fast-neutron spectrum. They contributed to plutonium breeding, electricity generation, and the accumulation of extensive operational experience, underpinning Russia’s continuing work on fast reactors and closed fuel cycles.

The technical evolution of these small liquid-metal reactors reflected careful adaptation to each coolant's properties. Sodium offered excellent heat transfer but was highly reactive with air and water, requiring careful control. Sodium–potassium alloys remained liquid at room temperature, simplifying some operational challenges in compact reactors. The eutectic lead–bismuth mixture, although dense and potentially corrosive, has a high boiling point and low neutron activation products, making it ideal for high-performance submerged vessels and autonomous underwater systems. Each choice dictated specialized materials, chemistry management, and operational procedures, shaping the capabilities and limitations of the final designs.

Understanding Poseidon’s propulsion is impossible without this context. It is the culmination of decades of experimentation with compact liquid-metal reactors, first honed for high-speed submarines and later refined in experimental and space-based reactors. The Soviet and Russian expertise in this field has created a vast knowledge base in coolant chemistry, thermionic conversion, and high-power-density reactor cores that underpins the design of autonomous nuclear-propelled systems capable of extraordinary range and power. The Poseidon story, both its public revelations and its technical mysteries, is inseparable from the long, intricate history of small liquid-metal nuclear propulsion in Russia, where innovation often outpaced safety, secrecy shaped the flow of information, and the extraordinary became operational reality.

Propulsion

In addition to its onboard nuclear reactor, propulsion is crucial for guiding the Poseidon to its intended target. Although detailed technical information is limited, a few publicly available photos, especially those showing the rear section, albeit partially obscured, along with conceptual sketches, suggest that Poseidon likely uses a pump-jet propulsion system. This type of propulsion is known for being quiet, efficient, and highly suitable for long-range underwater travel. Its low acoustic signature and enclosed design make it ideal for a strategic weapon intended to move undetected across vast ocean distances.

Instead of using traditional propellers, pump-jet systems pull water in through an intake, push it through a spinning rotor, and then force it out the back to create thrust. The entire mechanism is enclosed in a tube, making it safer and more streamlined.

The pump-jet model

One of the most significant advantages of pump-jet propulsion is its quiet operation. Because the moving parts are inside a casing, it doesn’t make as much noise as regular propellers. This is important for missions that require stealth, such as military or wildlife observation. It also helps reduce cavitation, which occurs when bubbles form and collapse around the propeller, causing noise and damage.

Pump-jets are also good at handling debris and rough underwater environments. Since the blades are protected, they’re less likely to get tangled or damaged. Some designs even allow the vehicle to move in any direction, which helps with maneuvering in tight spaces.

There are many new developments in this area. Some pump-jets are being made with 3D printing, which makes them cheaper and easier to customize. Others use special shapes and fluid-flow tricks to improve performance at low speeds. Some high-end models can dive deep underwater and still work efficiently, while newer designs are eliminating traditional shafts to make the system simpler and more reliable.

Of course, pump-jets aren’t perfect. They can be less efficient than propellers at very low speeds, and designing them requires extensive testing and fine-tuning. But engineers are working on ways to improve them, including using artificial intelligence to control their motion and exploring nature-inspired designs to make them even quieter and more efficient.

Challenge for the Sonar Operators

Sonar⁷ is the primary tool used to find submarines. There are two main types: active sonar, which sends out sound pulses and listens for echoes, and passive sonar, which listens for sounds in the water. Passive sonar is especially important for detecting quiet submarines, such as those using pump-jets.

Pump-jets are quieter because they reduce cavitation, the formation of bubbles that collapse and make noise. They also shield the moving parts within a duct, helping muffle the sound. However, they’re not entirely silent. Sonar operators are trained to listen for subtle acoustic signatures, such as the faint hum of machinery, vibrations from the pump-jet’s rotor and stator, or even the sound of water flowing through the duct.

Detection becomes a game of patience and skill. Operators use advanced sonar arrays and software to filter out background noise and focus on specific frequencies. They analyze patterns, compare them to known submarine profiles, and use techniques like target motion analysis to estimate the location and movement of a contact. In some cases, they rely on multi-static sonar, in which one system sends a signal and others listen for the return, increasing the chances of detecting a quiet submarine.

Despite the challenges, pump-jet submarines or autonomous underwater vehicles can still be tracked, especially if they operate in noisy environments, use older equipment, or have their propulsion systems start to wear down and produce more sound. For example, even the advanced Russian Borei-class submarines, which use pump-jets, have been detected due to aging hydraulic pumps that became noisier over time.

As Poseidon moves faster, potentially exceeding 100 km/h, it generates more noise from water flow, turbulence, and mechanical vibrations. This makes it easier for sonar operators to pick up its acoustic signature, especially if they’re using sensitive arrays designed to detect subtle underwater sounds.

But here’s the catch: even if Poseidon becomes more detectable at high speeds, intercepting it is another story. At such a velocity, it can cover vast distances quickly, reducing the time available for response. Traditional anti-submarine weapons and interceptors may struggle to match its speed or predict its path in time to neutralize the threat.

In essence, Poseidon trades some stealth for speed, but at such extreme velocities, it may not need to hide. Its ability to outrun most underwater defenses could make it nearly unstoppable once launched.

Warhead - the Tsunami-maker (or not)?

The warhead estimates are extreme—from generally clustering around two megatons, suggesting a large thermonuclear device packaged to withstand deep-sea pressures and long transit times, to a gigantic 100-megaton warhead, which is also feasible. Speculation about “salted” or radiologically enhanced versions, such as cobalt-based warheads designed to maximize contamination, persists in public discourse. Still, there is no reliable evidence supporting their existence at the time this article was published. From an engineering standpoint, very high yields would increase warhead size and mass beyond what a torpedo-sized body could efficiently accommodate. Hence, the two-megaton to ten-megaton range remains the credible estimate for now. Such a yield is more than sufficient to devastate any port or coastal city if detonated nearby.

Understanding the effects of a Poseidon detonation requires recalling the physics of underwater nuclear explosions. When a nuclear device explodes underwater, the expanding fireball creates an immense pressure wave through the surrounding water, known as a hydraulic shock, capable of crushing ships and underwater structures within a considerable radius. The explosion also generates a massive bubble of hot gases that oscillates, sometimes breaching the surface and ejecting a towering column of water. At shallow depths, this interaction forms a “base surge,” a cloud of radioactive mist that can heavily contaminate surrounding areas. Historical tests, such as the 1946 Baker shot at Bikini Atoll, demonstrated that even relatively low-yield underwater explosions can render ships and nearby waters dangerously radioactive for extended periods. In deep-water detonations, the shockwave and thermal energy remain more confined, causing less surface disturbance but still creating catastrophic conditions for marine life and infrastructure within kilometers.

Public claims that a Poseidon detonation could generate a “radioactive tsunami” capable of inundating entire coastlines across oceans are scientifically unsupported. Tsunamis arise primarily from the displacement of large volumes of water, typically by tectonic or landslide events that deform the seafloor over vast areas. A nuclear explosion, even at megaton scale, releases immense energy but couples it into short, high-frequency waves that dissipate rapidly rather than forming the long-wavelength motions required for ocean-spanning tsunamis. At most, a nearshore or shallow-water detonation could produce powerful local waves and flooding within tens of kilometers of the site, especially if it destabilized seabed sediments or triggered an underwater landslide. However, the global “continent-destroying tsunami” motif belongs more to political rhetoric than hydrodynamic reality.

The damage to a coastal city from a Poseidon strike would depend strongly on depth and distance. A deep-water detonation several hundred meters offshore would annihilate ships and marine installations nearby, create a massive plume of contaminated seawater, and leave severe radiological pollution in local currents and sediments. The water–air interface would mute the direct blast effects on land, though low-lying coastal facilities could still experience flooding and contamination. If the explosion occurred in shallow water, near a harbor or estuary, the destructive potential would rise dramatically. The blast would excavate the seabed, hurl millions of tons of water and radioactive spray onto the coast, and flood port districts with contaminated slurry. Ports, industrial zones, and densely populated waterfronts would suffer catastrophic damage. At the same time, aerosolized fission products and activated seawater could deposit dangerous levels of radiation across nearby areas for months and years. Even so, the primary inland hazard would stem from radioactive contamination and flooding, not from the kind of overpressure damage typical of atmospheric nuclear detonations.

The environmental consequences of such an event would be devastating. Marine life in the detonation zone would be destroyed instantly, and residual radionuclides could persist in sediments and food chains for decades. Fisheries and coastal economies would be crippled by contamination, and recovery of port infrastructure might take decades.

Some technical thoughts on when Poseidon goes boom…

What happens on the receiving end when Poseidon goes boom near the coastline can be simulated with software packages such as ANSYS for a serious, professional analysis, or even with an AI to a very broad degree, which can run different scenarios based on specific parameters.

Underwater shock from hypothetical megaton-class detonations using a standard empirical scaling relation commonly used in underwater-explosion engineering. The relation estimates the peak pressure in the water as a function of explosive yield and radial distance. In simple form, the equation used is:

Pₚₑₐₖ = 52.4×10⁶ · (W^{1/3} / R)^{1.13}, [Pa] ,

where W is the TNT-equivalent mass in kilograms and R is the distance from the explosion in meters. This formula is an engineering empirical fit (a Cole-type scaling) that produces reasonable first-order estimates of the short, intense pressure pulse a large underwater blast would create; it is not a substitute for a full numerical hydrocode simulation that includes depth, seabed geometry, bubble dynamics, or coastal bathymetry.

To get a wider picture of the effect, the formula mentioned above was run for four hypothetical yields that bracket commonly-discussed public estimates for a weapon of the Poseidon class: 0.1 Mt, 1 Mt, 2 Mt, and 10 Mt. Distances were evaluated from 100 m up to 100 km on a log-spaced grid, so the results show how the peak underwater pressure decays with range over two orders of magnitude and more.

The computed outputs are peak underwater pressures in MPa and psi, and grouped the numerical values into practical “damage bands” for intuition: pressures above ~100 MPa are inside the catastrophic range for nearby ships and submerged structures, 10–100 MPa is a severe-damage band, 1–10 MPa is serious (enough to breach small hulls or damage sensitive underwater systems), 0.1–1 MPa is significant, and below ~0.01 MPa the direct shock effects on large vessels or shore installations become small. These bands are approximate engineering heuristics, not precise structural failure thresholds, and are included only to help interpret distances in familiar terms. To present concrete numbers, here are the radii⁸ (rounded) at which the peak underwater pressure decays to selected thresholds for each yield I modeled. For 0.1 Mt, the radius to 100 MPa is about 260 m, to 10 MPa about 2.0 km, to 1 MPa about 15.4 km, and to 0.1 MPa about 118 km. For 1 Mt, those radii move outward: roughly 564 m to 100 MPa, 4.3 km to 10 MPa, 33.2 km to 1 MPa, and 255 km to 0.1 MPa. For 2 Mt, the comparable radii are about 711 m, 5.5 km, 41.9 km, and 321 km, respectively. For 10 Mt, they are roughly 1.22 km, 9.33 km, 71.6 km, and 549 km, respectively. These distances are the straight-line radial distances through water at which the modeled instantaneous peak shock falls to the stated pressure thresholds; they do not automatically map to “shoreline damage radii” without accounting for depth, geometry, and local bathymetry.

Interpreting what those radii mean in practice requires remembering two important physical facts. First, the pressure pulse in water is highly damaging at short distances because water transmits shock waves extremely effectively; ships and submarines within the inner radii listed above would receive lethal, structure-destroying loads. Second, converting that intense, short-wavelength energy into long-wavelength tsunami waves is inefficient. Large tsunamis that travel across oceans are produced most efficiently by rapid, large-scale vertical displacement of the seafloor (such as major earthquakes or massive submarine landslides), not by even huge explosions. What an underwater megaton-class explosion does do reliably is produce enormous local effects: if the detonation is deep and offshore you get brutally strong underwater shock and bubble dynamics that can crush or disable vessels and heavily contaminate the immediate water column; if the detonation is shallow or close to the shore the same energy couples strongly to the free surface producing violent local water columns, high local runup, violent coastal flooding in the immediate littoral zone, and a dense “base surge” and spray that can deposit activated and fission-derived radioactivity on beaches, ships and port infrastructure. In other words, shallow nearshore bursts are the worst-case scenario for a coastal city because they maximize both hydraulic damage and local radioactive contamination; deep bursts maximize underwater shock and subsurface damage but are less efficient at creating long-range tsunamis unless they trigger a significant submarine slope failure.

The numerical scaling is very useful for assessing the spatial extent of the short, powerful hydraulic shock, and it shows that multi-megaton yields push the serious-damage band (∼1 MPa) out to tens of kilometers in many cases. However, the scaling omits several phenomena that strongly affect actual coastal outcomes: the depth of the burst and how the expanding gas bubble interacts with the sea surface or the seabed (for example, a bubble striking the surface amplifies air blast and water columns), local bathymetry and coastal geometry (bays, shelves and estuaries can focus or amplify waves), bubble oscillation and the creation of a base surge that carries contamination inland in aerosol form, and the complex oceanographic transport of dissolved and particulate radionuclides. It also omits the distinction between short-wavelength wave energy (which explosions readily generate) and long-wavelength tsunami modes. Historical underwater nuclear tests such as Operation Crossroads Baker (23 Kt in shallow water) demonstrate the practical combination of strong local destructive power and intense radioactive contamination, but did not generate ocean-spanning tsunamis; modern analytical literature concurs that even megaton-class explosions are not efficient tsunami generators on a basin scale unless they trigger a massive submarine landslide.

The following are screenshots of the Excel spreadsheet results:

Poseidon 2 Mt warhead underwater peak pressures

Poseidon 10 Mt warhead underwater peak pressure

An Example - London, UK

Let us now clarify the previous text, which may be too technical for some readers, with a concrete example: London, UK. Assume that the largest warhead is used. A 100-megaton underwater nuclear detonation near London would be a catastrophic, city-devastating event, causing immediate mass fatalities in the blast zone, severe structural damage over a far wider area from underwater shock and hydrodynamic effects, extensive radioactive contamination of the sea and shoreline, and profound long-term social, economic, and environmental consequences. While the precise pattern of destruction would depend on variables such as exact location (distance from shore, detonation depth, local seabed topography), tidal conditions, and weather, the following broad effects would hold across all plausible scenarios.

If the device detonated in the Thames Estuary or just a few kilometers offshore, the first effect would be an immense underwater shockwave. Because water is nearly incompressible, a large portion of the weapon’s energy would propagate as a violent pressure pulse through the water column. Close to ground zero, this would obliterate ships, shatter piers and coastal defenses, and severely damage submerged infrastructure. Onshore, the shockwave coupling into the seabed would induce strong ground shaking, compromising building foundations, tunnels, and buried utilities.

At the detonation point, a colossal column of water, tens to hundreds of meters high, would erupt skyward before collapsing back in a roiling plume of spray. This collapse could generate a rapidly advancing surge or series of large waves directed toward the coast. Whether these evolve into an actual tsunami capable of flattening the city depends on technical factors like yield, depth, and seafloor geometry. While oceanographers dispute claims of continent-scale tsunamis from single explosions, a very large shallow-water burst near shore would likely produce waves powerful enough to inundate low-lying areas of the estuary, sweep away riverside structures, and violently flood parts of London closest to the Thames, particularly its docks and waterfront districts, transport corridors, and riverine infrastructure.

Thermal effects from an underwater burst are significantly muted compared to an airburst, as water absorbs most of the initial thermal pulse. Nevertheless, secondary fires would likely erupt from ruptured gas lines, electrical arcing, and building collapses, potentially igniting widespread conflagrations across the damaged urban area. The explosion would also produce a massive “base surge”, a dense, fast-moving cloud of radioactive mist composed of pulverized seawater and particulate debris, which could be driven inland by wind, coating streets, buildings, and people with contamination.

Radioactive dispersal from an underwater detonation differs markedly from that of an airburst. Much of the fallout becomes entrained in water, rendering the surrounding sea and any aerosolized spray highly radioactive. Fine droplets and contaminated sediments can be carried inland, depositing localized but intense radioactive hotspots, especially near the shoreline. Unlike the fine, windborne fallout from high-altitude bursts, which can travel globally, a near-shore underwater explosion concentrates contamination in the marine environment and immediate coastal zone, yet that concentration is severe enough to render ports, beaches, and riverbanks hazardous for decades. Long-term bioaccumulation in marine life and sediments would pose additional public health and ecological risks.

The human toll would be overwhelming. In the immediate aftermath, those in the blast and inundation zones would face unsurvivable conditions: extreme overpressures, drowning, traumatic injuries from collapsing structures, and acute, lethal radiation exposure. Emergency response would collapse—hospitals, power grids, water systems, and communications in the hardest-hit areas would likely be destroyed or incapacitated. Blocked or obliterated access routes would cripple evacuation and rescue operations. In the following days and weeks, thousands more would suffer from radiation sickness, infections, lack of clean water, and the breakdown of medical care. The psychological trauma, mass displacement, and loss of essential civic functions would trigger nationwide and global ripple effects.

Environmental and economic consequences would be extreme and enduring. The Thames Estuary and adjacent coastal ecosystems would be heavily contaminated; critical maritime infrastructure such as ports, docks, and shipping lanes could remain unusable for years or decades. Decontaminating radioactive seawater, removing contaminated sediments, and rebuilding destroyed infrastructure would require unprecedented resources and time, costing an astronomical, though uncertain, sum. Given London’s role as a global financial and logistical hub, the disruption to international trade, finance, and supply chains would be profound. Politically and militarily, such an attack would provoke an immediate and severe international crisis with far-reaching geopolitical ramifications.

It is crucial to acknowledge uncertainty and avoid sensationalism. A 100 Mt yield is extraordinary, double that of the largest nuclear test ever conducted (the Soviet Tsar Bomba, app. 50 Mt), and experts remain skeptical of exaggerated claims, such as continent-spanning tsunamis from a single device. Slight variations in depth, location relative to the estuary mouth, or local bathymetry can dramatically alter wave behavior, focusing or dissipating energy along different stretches of coast. Yet even accounting for these uncertainties, a near-shore detonation of this magnitude would constitute an unparalleled disaster for London and the surrounding region.

The Poseidon carrier

Positioning Poseidon close to a target necessitates a dedicated underwater carrier. Although its nuclear propulsion eliminates practical range constraints and technically allows launch from Russian territorial waters, employing a submarine-based launcher affords the operational flexibility to deploy and launch the system from nearly any location.

In the Russian Navy, there are two distinct platforms designated as autonomous nuclear undersea vehicle carriers. These are submarines Belgorod and Khabarovsk. The development of these two submarines reflects a deliberate Russian effort to create undersea platforms that are not simply conventional attack (hunter-killer SSN) or ballistic-missile submarines (SSBN) but rather purpose-built carriers for long-endurance autonomous systems and special-mission payloads. Belgorod, the first of these platforms to be publicly acknowledged in Western sources, began life as a Project 949A (Oscar-II) hull before being heavily reworked into Project 09852; the conversion produced a huge submarine with internal volume allocated to deployable vehicles, hangars, and specialized mission systems rather than a pure loadout of cruise missiles. Publicly available technical descriptions place Belgorod’s submerged displacement in the tens of thousands of tons and its length in the high-170s to mid-180s—numbers that make it among the largest operational submarines in the world and align with its role as a “mother ship” for unmanned systems and large payloads.

Belgorod submarine evolution. Credit to CovertShores.

Open reporting indicates Belgorod was modified to carry multiple Poseidon vehicles—commonly cited figures are up to six—installed in external or internal launch bays sized for large torpedoes or autonomous vehicles. This connection between Belgorod and Poseidon is the principal basis for labeling Belgorod a strategic as well as a special-mission asset: if Poseidon is fielded with a nuclear warhead and long endurance, then the hosting submarine becomes part of Russia’s strategic deterrent architecture, not merely an experimental platform. That said, open sources emphasize that many operational details, such as internal launch mechanisms, command-and-control links, and the actual warhead and propulsion characteristics of Poseidon, remain officially opaque.⁹

Project 09852 Belgorod. Credit to CovertShores.

Khabarovsk is the follow-on design intended from the outset to be a dedicated Poseidon carrier. Projected in open sources as Project 09851 (sometimes reported as 08951), Khabarovsk represents a different design philosophy: instead of converting a large existing hull, the navy sought a purpose-built class with specific bays and systems for serial carriage of multiple large autonomous torpedoes. Imagery and reporting in 2024–2025 indicate that Khabarovsk has been launched and is proceeding through outfitting and trials; the vessel is described as smaller than Belgorod but optimized to carry more Poseidon units in a production series, thereby moving the capability from a single testbed to an operational class. Open analysts caution that construction and commissioning schedules, and the actual Poseidon numbers fitted to each boat, can change with program priorities and technical hurdles.

Project 09851 Khabarovsk. Credit to CovertShores.

Khabarovsk with distinctive and obscured pump-jet propulsion.

Technically, the combination of a large carrier submarine and a nuclear-powered underwater vehicle presents several distinctive engineering and operational challenges and opportunities. From a systems perspective, the carrier must provide physical launch capability (a bay, cradle, or vertical/horizontal ejector sized for a vehicle the size of a massive torpedo), onboard handling systems, environmental control for long-endurance payloads, data and communications links for mission tasking and telemetry, and maintenance and recovery facilities where relevant. Belgorod’s conversion work and internal images suggest space and handling systems large enough to support these needs; a purpose-built Khabarovsk can be expected to integrate such systems more tightly, reducing the need for field modifications and improving sortie rate. Critics and independent analysts also point out survivability trade-offs: larger hulls with mission bay apertures and external fairings may exhibit acoustic and hydrodynamic signatures different from those of attack or ballistic missile submarines, potentially affecting detectability and transit profiles.

Operational concepts for employment fall into several broad but overlapping categories: strategic deterrence, area denial and coastal-targeting, and long-endurance reconnaissance or strike missions using autonomous systems. If Poseidon is indeed a nuclear-armed, long-range, nuclear-powered vehicle, then deployment options range from forward positioning within Russian territorial waters to covert transit and deployment from patrol areas in the Arctic, North Atlantic, or Pacific approaches. Belgorod’s size and sensor/communications fit suggest it can operate as a forward staging platform, carrying a small number of Poseidon vehicles to areas beyond Russia’s littorals where they can be released toward targets. Khabarovsk, as a serial Poseidon carrier, would allow more distributed, redundant deployments across fleets and theaters. In practice, operational commanders would weigh the risk of exposing the carrier against the value of forward basing: keeping the carrier in safer home waters reduces transit risk but lengthens the torpedo’s required undersea transit; forward deployment shortens it but raises the chance of detection and loss. ¹⁰

A concrete operational routine could therefore look like this in plausible terms informed by open reporting and naval practice: the carrier receives mission tasking and vehicle loadout in port, sails on a long transit under stealth to a designated patrol area, establishes a low-profile surveillance posture while exchanging encrypted tasking and targeting data with higher command and perhaps space or over-the-horizon sensors, and then, under favorable conditions, releases one or more autonomous vehicles to proceed to designated waypoints or target areas. Communications architecture is critical in that sequence; the vehicles must be sufficiently autonomous to complete missions when comms are limited, and the carrier must retain the ability to abort, recover, or re-task assets if required. Open sources indicate Belgorod has been used extensively in trials with unmanned underwater vehicles and that Russia has experimented with surface support ships for Poseidon work, suggesting a mixed fleet approach to testing and, potentially, operations.¹¹

Strategic and operational implications are manifold and deserve careful caveats. From a deterrence standpoint, weapons that can loiter or approach coastal targets from undersea approaches potentially complicate adversary defenses and raise the political threshold for conflict. However, Poseidon’s alleged capabilities, such as endurance, speed, depth, and warhead yield, have been variably reported, sometimes with sensational figures; open intelligence and independent technical analysis vary in confidence about the precise destructive mechanisms (for example, the feasibility of a naval detonated yield producing a tsunami of strategic scale is debated by oceanographers and weapons scientists). Public statements by Russian officials announcing tests or capabilities tend to be politically salient and should be cross-checked with technical analysis; independent outlets and technical observers have documented tests and trials, but cannot independently verify every performance claim made by national leaders. The most responsible analytical posture is to accept that the systems exist and are being integrated, while treating specific performance claims, especially catastrophic tsunami scenarios, with careful skepticism unless independently corroborated.

On force posture and command and control, integrating autonomous nuclear vehicles with strategic command systems creates complex authorization and safety challenges. Any credible deployment doctrine would have to address secure release authority, fail-safe measures, environmental monitoring to reduce fratricide and unintended impacts, and maintenance of communication with assets that may be designed to operate submerged for long periods. Open sources do not and cannot reveal classified command procedures, but observers note that Russia’s long history of special-mission submarines operated by civilian-run research directorates (for example, its Main Directorate for Deep-Sea Research) implies a separation between conventional fleet command and the organizations that might task strategic autonomous systems. That separation raises both procedural ambiguity and potential escalation risks if operational control is diffused across military and civilian research entities.

Because much of the technical truth about Poseidon’s propulsion, guidance fidelity, and warhead characteristics is withheld from public view, prudent analysis emphasizes scenario planning over definitive claims. One scenario with moderately conservative assumptions is that Belgorod and Khabarovsk will be used primarily as strategic backups and testbeds for autonomous underwater weapons—deterrent signaling tools that increase uncertainty for regional adversaries, but not as large numbers of first-line strike assets. An alternative, more aggressive scenario is that Khabarovsk-class boats are produced in modest numbers and assigned to fleet areas to create multiple dispersed launch nodes for autonomous strategic payloads. Which scenario unfolds depends on technical maturation, budgetary choices, crew training, and geopolitical signaling objectives. Open reporting from 2024–2025 suggests Russia is at least moving from testbed to serial buildout, but the scale and tempo of that shift remain subject to programmatic and diplomatic variables.¹²

From a policy and stability perspective, the emergence of submarines purpose-built for autonomous nuclear systems raises questions for arms control, surveillance and antisubmarine warfare, and crisis management. Existing arms control instruments were not written with underwater autonomous nuclear vehicles in mind, and the opaque nature of special-mission conversion work complicates transparency measures. For navies and defense planners in other countries, the operational priority will be improving undersea detection, tracking, and attribution capabilities; for policymakers, the task will be considering whether new confidence-building measures or technical verification regimes are needed to reduce the risk of miscalculation in crises involving novel submarine-launched autonomous systems.

Summary

In summary, the Poseidon system represents a technically feasible but strategically extreme extension of known nuclear and naval technologies. It most likely uses a compact liquid-metal-cooled fast reactor to achieve long-range, high-speed operation at great depths, carries a warhead of 2-100 Mt, and could inflict catastrophic local damage and contamination on any coastal target. Yet the notion that it could raise ocean-wide radioactive tsunamis is unsupported by physical science. Its true significance may lie less in its physics than in its symbolism: a weapon designed to project the image of ultimate deterrence by threatening entire coastal societies, even if the practical mechanics of such annihilation are more limited than popular imagination suggests.

Politically, the deployment of Poseidon adds a new dimension to strategic deterrence. Its autonomous nature and perceived “doomsday” capability suggest a weapon intended more for psychological and geopolitical signaling than for practical battlefield use. Its mere existence challenges traditional arms control frameworks and complicates stability calculations by introducing a new underwater axis of nuclear deterrence.

Despite the growing public literature, many details remain unknowable. The reactor’s design, actual performance, warhead configuration, and even deployment status are tightly held secrets. Modeling the hydrodynamics of a multi-megaton underwater detonation is inherently uncertain, as no full-scale tests have ever been conducted at such yields or depths. Extrapolations from smaller historical tests provide useful guidance but cannot capture all nonlinear effects of deep-water bubble dynamics or coastal interactions. Moreover, the strategic intent behind Poseidon, whether as a second-strike deterrent, a terror weapon, or an anti-access denial system, remains speculative and politically sensitive.

If you like the article (and many more articles regarding military subjects will come), you can buy me a coffee:

https://www.buymeacoffee.com/mmihajloviW

---

[i] Edited by Piquet (EditPiquet@gmail.com).

1. For comparison, the biggest ever nuclear bomb detonated on 17 October 1961 was the Soviet Tsar-Bomba (AN602) with a yield of 50-58 Mt.

2. IAEA technical report: Liquid Metal Cooled Reactors: Experience in Design and Operation (TE-1569) - review of liquid-metal reactor experience (sodium, lead-bismuth) and materials/operational issues.

3. “Lead-bismuth cooled reactors: history and the potential of …” (technical review) — discussion of LBE history and the 1958 prototype onward.

4. TOPAZ nuclear reactor overview (history of TOPAZ-I / TOPAZ-II; Kurchatov Institute involvement; US purchases/testing in the 1990s).

5. BM-40A / OK-550 descriptions and Project 705 technical notes (Alfa class submarine reactor details).

6. World Nuclear Association / ARIS materials on BN series and Beloyarsk BN-600/BN-800 operations.

7. Sound Navigation and Ranging

8. Radii is the plural of radius.

9. https://www.naval-technology.com/projects/k-329-belgorod-nuclear-powered-submarine-russia/

10. https://www.naval-technology.com/projects/k-329-belgorod-nuclear-powered-submarine-russia/

11. https://www.twz.com/sea/powered-test-of-poseidon-nuclear-torpedo-putin-claims

12. https://www.thebarentsobserver.com/security/here-comes-russias-first-serial-submarine-to-carry-nuclearpowered-gigatorpedoes/439639