NATO has warned that Vladimir Putin has deployed Russia's K-329 Belgorod nuclear submarine which is a carrier of apocalypse underwater drone Poseidon.
The Russian weapon is a giant nuclear-capable torpedo capable of causing radioactive tsunamis that can lay waste to enemy coastlines.
Russian TV propagandist Dmitry Kiselyov notoriously told viewers that Russia should “plunge Britain into the depths of the sea” with its “underwater robotic drone Poseidon” causing a 1,640ft tsunami.
Details of its unique high speed 125mph underwater propulsion system have been a closely guarded Russian secret.
The 604ft-long Belgorod is reportedly submerged in Arctic waters after it is suspected of involvement in sabotaging the Nord Stream gas pipelines, according to unofficial sources.
The report of an intelligence note sent by NATO comes from Italian newspaper La Repubblica.
Its mission in the Arctic is feared to be to test the Poseidon super torpedo, seen by Putin as a key to his ultimate military supremacy over the West, according to the report.
This comes amid Russian sabre-rattling over the use of nuclear weapons linked to the Ukraine war, where Putin has been stymied by Western arms supplies.
The Belgorod can go up to 120 days without having to return to the surface.
TASS has previously reported that the Poseidon drone has an unlimited range and a maximum speed of more than 125 mph.
"Unique characteristics of the Poseidon system will help the Navy to successfully combat aircraft carriers and strike groups of a potential adversary in any oceanic theatre of war and destroy shore infrastructure facilities," stated chief analyst of the General Staff, Admiral Igor Katasonov.
"It is a completely new type of weapon that will force Western navies to change their planning and develop new countermeasures," said expert H I Sutton, as reported by La Reppubblica.
A video shows how the state-of-the-art Belgorod submarine carries the lethal Poseidon drone torpedo.
Kiselyov - avidly watched by Putin and a top executive in Moscow’s powerful state media propaganda machine - said Russia could use its big beast Sarmat hypersonic missile, also known as Satan-2, against Britain.
But he told viewers in May: “Another option to plunge Britain into the depths of the sea is the Russian underwater robotic drone Poseidon.
“It approaches the target at a one kilometre depth with the speed of 200 kilometres per hour [125mph].
“There is no way to stop this underwater drone.
“It has a warhead with a capacity of up to 100 megatons.
“The explosion of this thermonuclear torpedo close to Britain's shores will raise a giant wave, a tsunami, up to 500 metres [1,640ft] high.
"This tidal wave is also a carrier of extremely high doses of radiation.
“Surging over Britain, it will turn what is probably left of them into radioactive desert.
“Permanently unusable for anything.
“How do you like this prospect? And Putin warned about this, back on February 24 [if anyone interfered with his special military operation].”
Putin accused the West of sabotaging the Russian-made Nord Stream pipelines, but Western sources insist Moscow was behind the stunt which led to huge gas leaks in the Baltic.