Russia is allegedly building a 'doomsday' torpedo with the nuclear capability to wipe out coastal cities.
A copy of the United States Defense Intelligence Agency's nuclear posture review, which was leaked in January, reveals that the Pentagon is ramping up its nuclear efforts to focus on the threat posed by Russia.
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The report states that Russia is developing a "new intercontinental, nuclear armed, nuclear-powered, undersea autonomous torpedo".
It describes the weapon, known by the codename 'Kanyon', as a drone-type device which is fired underwater and designed to create large zones of radioactive contamination.
Armed with a 100-megaton hydrogen bomb (twice as powerful as any nuclear bomb ever tested), the torpedo would 'swim' through the ocean toward its target, resistant to anti-missile systems.
Once detonated, the resulting nuclear blast could swamp coastal areas by creating a radioactive tsunami up to 500ft high, which could destroy a city and leave the land uninhabitable for up to a century.
Some analysts have called Kanyon a "doomsday weapon", while scientist Adam Mount told CNN that the torpedo is a "horror of the Cold War".
"It is clearly inspired by overblown Russian worries that US missile defenses will make their missile forces obsolete."
He said it was "alarming" to see the torpedo mentioned in an official Pentagon document.
In addition to Kanyon, the report estimates that Russia has a stockpile of 2000 "non-strategic" nuclear weapons. These include short-range ballistic missiles, unguided 'gravity' bombs and 'depth charges' designed to attack submerged submarines.