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Why Russia’s Massive Poseidon Nuclear Torpedo Is So Terrifying

Poseidon Nuclear Torpedo
Image: Creative Commons.

Poseidon is massive — and basing the torpedo on the ocean floor could make it impossible to stop.

The Threat

The Russian Navy’s fearsome Poseidon torpedo is not only nuclear-armed, but it is also nuclear-powered. And it is massive — estimated at around 7 feet in diameter and around 100 tons, the torpedo foregoes a conventional high-explosive warhead in favor of a nuclear payload. By comparison, one of the United States Navy’s standard heavy-weight torpedos, the Mark 48, is a paltry 21 inches in diameter and about 3,500 pounds.

Unlike most conventional torpedoes, the Poseidon’s primary target wouldn’t necessarily be a surface ship or other submarines. Thanks to the torpedo’s large nuclear warhead, it would instead target large port cities vital to industry and trade — like the many cities that dot the United States’ east and west coasts.

New Deployment Strategy?

Despite Poseidon’s massive offensive potential, the nuclear weapon has one potentially glaring weakness: its delivery method.

The Poseidon’s range is virtually unlimited, and combined with a high top speed, would be a particularly challenging weapon to defend against. However, for a Poseidon launch to be successful, the submarine the torpedo launches from must remain undetected — at least long enough to fire off its nuclear payload.

Poseidon’s considerable size requires a massive launch platform: the Russian Navy’s K-329 Belgorod submarine.

K-329 Belgorod

While Russian Navy submarines have made significant advances in improving their stealth capabilities, Soviet submarines have historically been considered ‘loud’ compared to their American and NATO Ally counterparts.

The Belgorod was originally a Soviet-era Oscar II-class nuclear submarine but features several modernizations and improvements. In addition to serving as a mothership to six Poseidon torpedos, the large submarine hosts a deep-diving, nuclear-powered midget submarine mated under its hull and an unmanned underwater vehicle inside a topside hangar.

Given the K-329’s auxiliary vehicle’s unique capabilities, experts believe that the Belgorod plays dual roles: an intelligence collection and espionage platform and a powerful sea-based leg of Russia’s nuclear deterrence triad.

A Threat from Below

Recent open-source intelligence suggests that the Russian Navy is aware of their submarine noise issues and is actively masking the Poseidon before launch. How? Not by launching the missile from a submarine but a fixed ocean floor location.

Independent of a submarine, a Poseidon torpedo could theoretically lie in wait for extended periods of time, perhaps in a kind of launch container to protect the torpedo from the corrosive effects of the sea and ocean flora and fauna. When signaled, the torpedo could then blast outwards and toward a coastal city target.

The launch method trade-off is not without its own problems, however. Removed from a submarine mothership, a containerized Poseidon would be extremely vulnerable if located by an opposing naval force, possibly defenseless. Furthermore, a fixed seabed position could limit the torpedo’s application, although this may be somewhat mitigated by high top speed and virtually unlimited range.

Oscar II-class Submarine 3

Image Credit: Facebook posting from Danish Navy.


The Poseidon nuclear torpedo is clearly a weapon with incredible offensive potential. In addition to a seabed or submarine launch, some experts believe the torpedo could travel ‘stealthed-up’ towards a target, masking its sound by traveling slowly until it reaches its target. Regardless of which launch method is ultimately favored, the Poseidon is a potent arrow in the Russian Navy quiver.

Caleb Larson is a Defense Writer based in Europe. He holds a Master of Public Policy and covers U.S. and Russian security, European defense issues, and German politics and culture.

Written By

Caleb Larson is a multiformat journalist and defense writer based in Berlin but has spent most of 2022 reporting from Ukraine. He covers the intersection of conflict, security, and technology, with a focus on American foreign policy and European security. Follow him on Twitter @calebmlarson.



  1. Rich Streeter

    September 3, 2021 at 10:23 am

    That’s not a torpedo, that’s a weaponized UUV. Words and definitions matter. Scary non-the-less, but realistically, any nation that can produce a UUV can rig a nuke warhead inside of it. Welcome to the year 2021.

  2. Frank

    September 3, 2021 at 12:30 pm

    While it’s interesting from a technological perspective, Poseidon is no more terrifying than a nuclear-armed ICBM, and is in fact probably less so all things considered.

    Popular layman-level defense industry/security journalism sites have been hyping it up as some amazing doomsday weapon, but it’s just a mobile nuclear depth bomb. Nothing about it changes deterrence theory in any meaningful way.

    Poseidon can’t target landlocked or inland strategic targets, which is a huge downside, and it has far greater travel time to target than an ICBM. SOSUS could detect it en-route, but if it were able to “sneak up” on a costal target it could create strategic surprise. However, since it wouldn’t be able to counterforce target inland ICBM silos, it’s only valuable for countervalue targeting, thus defeating the purpose of said surprise attack, since the target’s land-based nuclear forces would be able to make a retaliatory strike.

  3. Brian Reilly

    September 3, 2021 at 2:11 pm

    Oh my GOSH!! The Russkies have a weapon we MUST counter! Alert GD, Lockheed, Boeing… all of them. Throw massive amounts opf cash at the problem now, before it is too late!!

    And you people wonder why we taxpayers want to run you all out of town on a rail…

  4. Geary Carson

    September 3, 2021 at 9:48 pm

    Well, this is where you want the mean guy as President. I don’t think anyone believes that the military could do much of anything now let alone detect Russian submarines in time to stop a massive nuclear weapon. With Former Vice President Biden the Commander In Chief, we are all sitting ducks just gambling that we can survive this presidency cycle.

  5. Mb

    September 7, 2021 at 12:42 am

    An expensive, redundant waste of money. We should encourage the Russians to build as many as possible.

  6. Tom Bombastadillo

    April 15, 2022 at 3:18 pm

    If the range is unlimited, they can just fire them from home base. And if they can self-propel in stealth all by themselves, then just launch them from home base. That seems to negate most of the premise of this article.

  7. Steven

    April 15, 2022 at 8:30 pm

    I kept saying that all the way through the article. Thinking no longer exists on the planet. “It cannot be sunk, but it’s greatest weakness is being sunk” Don’t take drugs and write online all you kids out there.

  8. victorian

    April 18, 2022 at 5:31 pm

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