Russia is in possession of an underwater nuclear drone capable of carrying a 100-megaton nuclear warhead, a recently leaked draft of the Pentagon's Nuclear Posture Review confirmed.

The weapon, referred to in the document as an “AUV,” or autonomous underwater vehicle, is featured in a chart that lays out Russia's multiple nuclear delivery vehicles.

Pentagon officials warn in the posture review that Russia has actively diversified its nuclear capabilities, a strategic advantage it has over the United States:

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In addition to modernizing ‘legacy’ Soviet nuclear systems, Russia is developing and deploying new nuclear warheads and launchers. These efforts include multiple upgrades for every leg of the Russian nuclear triad of strategic bombers, sea-based missiles and land-based missiles. Russia is also developing at least two new intercontinental range systems, a hypersonic glide vehicle and a new intercontinental, nuclear-armed undersea autonomous torpedo.

The draft of the posture review was obtained and published by the Huffington Post.

In a statement, the Pentagon did not deny that the draft is authentic...