Russia has once again sent a signal to the world. President Vladimir Putin proudly announced the successful test of the Poseidon, a twenty-metre-long nuclear underwater drone that Moscow claims is “impossible to intercept”. With a range of around 10,000 kilometres and an alleged payload of up to 2 megatons, Poseidon would be capable of destroying coastal cities in Europe or North America.

The question now occupying experts is this: if this super torpedo really works — how could anyone stop it?

A weapon of a new order

Poseidon is not a conventional torpedo. It is an unmanned, autonomous underwater drone powered by a miniature nuclear reactor. That allows the weapon to remain underwater for months and move at speeds of up to 100 kilometres per hour — far faster than most submarines or anti-submarine weapons can track.

According to Russian sources, Poseidon can travel at depths of up to one kilometre and imitate the acoustic signature of a civilian vessel along the way, making sonar detection extremely difficult. From Russian waters, the weapon could reach virtually any target in the Atlantic or Pacific Ocean.

Putin calls it an “invisible protector of Russia”, but within NATO it is seen as a strategically destabilising weapon: designed not to win a war, but to spread fear.

A new threat to existing defence systems

Until now, most missile defence systems — from the American Aegis network to Israel’s Arrow system — have been designed to intercept ballistic missiles in the air. An underwater drone such as Poseidon operates entirely outside that defensive layer.

“There is no defence system designed to intercept a nuclear warhead travelling underwater,” one NATO officer said off the record. “You can see missiles on radar, but not something moving kilometres below the surface.”

An additional problem is that Poseidon can be launched from special submarines such as the Belgorod class, which are themselves difficult to track. Once the weapon is on its way, it becomes practically untraceable — making it above all a psychological weapon of threat and deterrence.

Russia is playing with fear

Since the Cold War, Moscow has used nuclear weapons as a political pressure tool. According to Russia expert Jan Balliauw (Egmont Institute), Putin uses demonstrations like this to show that the West “must not mock Russia”.

Poseidon fits perfectly into that picture: technologically impressive, but above all intended to intimidate. Russian state media have even suggested that a coastal detonation could trigger a radioactive tsunami tens of metres high — although Western analysts consider that unrealistic.

Even so, the message is clear: deterrence through fear.

How do you defend yourself against something that seems unstoppable?

For Western defence analysts, Poseidon represents a new kind of threat that changes thinking about deterrence. Concepts exist for underwater drones designed to intercept other drones, but that technology is still in its infancy.

Some experts point to the need for new sensor networks that map the ocean floor worldwide, combined with AI-driven detection systems. Others stress that diplomacy and arms control will become crucial: if every major power develops a Poseidon-like system, underwater stability will be hard to maintain.

In other words, the world needs to think about defence now, before the first of these weapons becomes operational.

A new phase in nuclear threat

Putin’s “super torpedo” shows how the arms race has shifted once again — from the air to the depths of the ocean. Where missile shields once offered the illusion of protection, Russia is now literally going underneath that shield.

Poseidon is therefore more than a weapon: it is a warning that the future of warfare lies not only in the air or in space, but underwater as well. And as long as there is no answer to the question of how to stop it, Poseidon will remain a frightening symbol of modern nuclear power.