Packed with nuclear firepower and capable of taking out an aircraft carrier or even an entire city, this is the latest devastating weapon in Vladimir Putin’s arsenal – the world’s longest submarine.

To be launched tomorrow by the Russian President, the 604ft Belgorod is expected to be equipped with up to six nuclear-armed torpedoes, each capable of carrying warheads with an explosive power of two megatons – equivalent to two million tons of TNT, or more than 130 times the power of the Hiroshima bomb.

Experts fear the 79ft-long torpedoes – dubbed Poseidon or Kanyon – could be detonated underwater to cause a radioactive tsunami and threaten coastal cities with waves up to 300ft high.

The Belgorod is expected to operate in the Arctic and the North Atlantic – areas where Russian submarine activity has increased tenfold in recent years

In what is regarded as a sinister development, the submarine’s commanders will report directly to President Putin rather than to the country’s naval top brass, making Belgorod more like a deep-sea intelligence agency than a conventional submarine [File photo]

And there may be no defence for the new British aircraft carriers HMS Queen Elizabeth and HMS Prince of Wales – the largest warships ever built for the Royal Navy – against the nuclear torpedoes, which have a top speed of 70 knots and a range of thousands of miles.

The Belgorod sets sail from Severodvinsk on Russia’s Arctic coastline tomorrow. It carries eight unmanned underwater vehicles (UUVs) which can operate miles below the waves to map the ocean floor using a sonar imaging system known as side-scanning, but may also be deployed to sabotage undersea power and internet cables.

The giant sub also has a 180ft mini-submarine docked underneath it. The 25-man craft can be used for research, rescue and special military operations.

In what is regarded as a sinister development, the submarine’s commanders will report directly to President Putin rather than to the country’s naval top brass, making Belgorod more like a deep-sea intelligence agency than a conventional submarine.

Dr Sidharth Kaushal, from the Royal United Services Institute, told The Mail on Sunday he believed the fleet of UUVs could be of strategic value for Putin.

Dr Kaushal said: ‘The Belgorod is large enough to act as a mother ship for a unique set of smaller vessels which have deep-diving capabilities and the ability to tamper with undersea infrastructure.

So it is well equipped for sabotage and clandestine operations. Its Poseidon nuclear torpedoes could also be a very effective means of attacking an aircraft carrier in wartime – one against which at present no defence exists.

‘The Belgorod will not be part of the Russian Navy per se, meaning its covert and aggressive actions will effectively be deniable. The submarine appears set up for non-attributable Special Forces warfare with its commanders answering directly to the [political] leadership and bypassing the Russian naval command structure.’

The Belgorod is expected to operate in the Arctic and the North Atlantic – areas where Russian submarine activity has increased tenfold in recent years. There has also be a huge rise in Russian approaches to UK territorial waters.

In 2010, the Royal Navy had to respond to only one intrusion, but in 2017, 33 separate incidents required a response by British ships or submarines.

The Navy is developing its own fleet of UUVs, but they are not expected to enter service for another eight years, according to sources.