Russia has tested its nuclear-powered Poseidon underwater torpedo, President Vladimir Putin said, marking the country’s second strategic weapons trial in less than a week and prompting renewed debate over a potential new phase in nuclear deterrence.

Speaking during a hospital visit with soldiers wounded in Ukraine, Putin said the device was launched from a submarine and that its onboard nuclear power unit had been successfully activated. It was his most detailed public description of the programme in several years. He claimed the system could not be intercepted by existing technology.

“For the first time, we managed not only to launch it from its carrier submarine using the starting engine, but also to activate its nuclear power plant, on which the vehicle operated for a certain period of time,” Putin said, as quoted by the Kremlin.

“This is a major success because, like the Burevestnik, it has very compact dimensions. If the Burevestnik’s reactor is a thousand times smaller than that of a submarine, Poseidon’s is a hundred times smaller. Yet Poseidon’s power output significantly exceeds even that of our most advanced intercontinental missile, the Sarmat.”

The test follows Russia’s trial of the Burevestnik nuclear-powered cruise missile on October 21 and nuclear launch drills on October 22. The Kremlin described these actions as proof that Moscow would not yield to Western pressure over the war in Ukraine. The White House urged Russia to focus on ending the conflict rather than showcasing new weapons.

According to Reuters, analysts describe Poseidon as an autonomous, nuclear-powered torpedo designed to travel thousands of kilometres at high speed to strike coastal targets and contaminate shorelines.

Open-source assessments cited by Russian media indicate the system is about 20 metres long, weighs roughly 100 tonnes and could carry a warhead of up to two megatonnes, possibly using a liquid-metal-cooled reactor. Putin and state media have previously outlined operational parameters suggesting a range of 10,000 km at around 185 km/h.

Putin called the torpedo “unstoppable” as it travels deep under water at 1,000m below sea level, making it “undetectable” and suggested that no defence against the weapon can ever be developed.

“There are no methods of intercepting it,” he said. “And it is unlikely anything comparable will appear anytime soon.”

Putin said the Poseidon can be added to the list of the hypersonic Oreshnik,  the nuclear cruise missile Burevestnik,  Russia’s largest ICBM Sarmat, and a whole new class of hypersonic missiles which he showcased in during his 2018 state of the nation speech which the West has no analogue for. According to reports at the time, the Pentagon was taken by surprise by the hypersonic missiles and currently has no countermeasure. Specifically, the Burevestnik can penetrate the “Golden Dome” missile shield recently proposed by Trump.

The Poseidon is also a potential game changer and it also challenges traditional arms-control categories by combining a nuclear propulsion system with an autonomous delivery mechanism that is neither a ballistic nor a cruise missile. Moscow presents such projects as a response to decades of United States missile-defence developments and Nato’s eastward expansion.

The announcement appeared aimed at both domestic and international audiences: at home, to demonstrate technological progress despite sanctions, and abroad, to signal that Russia retains advanced nuclear capabilities even as its conventional war in Ukraine continues.

Nuclear tests back on

In apparent response to the string of announcements of new Russian nuclear weapons, US President Donald Trump ordered the newly renamed Department of War to restart nuclear weapons tests in defiance of the Comprehensive Nuclear Test Ban Treaty (CTBT) that the US signed in 1996, but never ratified. Despite the lack of ratification, the United States has maintained a unilateral moratorium on nuclear testing since it last exploded an atomic bomb in 1992.

Russia was also an original signatory to the agreement, and it ratified the treaty in 2000. However, the Kremlin revoked its ratification in in October 2023 but said it would maintain a moratorium on tests unless the US restarted its tests.

If Trump carries through on the order to resume testing, the collapse of another Cold War-era security agreements. The START missile treaty is due to expire next February that was renewed by Putin and former US President Joe Biden in 2021, but suspended by the Kremlin following the start of the war in Ukraine. Putin and Trump discussed renewing the treaty again during the Alaska summit on August 15 but as nuclear sabre rattling increases the prospects of that are fading.

Both America and Russia are becoming increasingly more aggressive with their nuclear posturing. Prior to the order to resume nuclear tests, Trump moved two nuclear submarines to an “appropriate place” in August as part of his tough man showdown with Putin as a deadline to end the war in Ukraine by August 15 loomed. That clash ended with an agreement to meet in Alaska instead.

Putin also loosened its nuclear doctrine last year, reducing the threshold for justifying a first strike on an adversary by broadening the definition of what defines an “existential threat” to Russia. The escalating threats and showcasing of increasingly powerful weapons is destabilising and increases the chances of a nuclear war, bne IntelliNews opined in an editorial in August.