Russia's new assassin sub has a fatal flaw

It's official. K-560 Severodvinsk, Moscow's newest and most advanced nuclear attack submarine, has joined the Russian navy.

That's bad news for most countries that could conceivably face Russia in a conflict. The expensive, quiet, 13,800-ton Yasen-class submarine is arguably one of the most sophisticated in the world — and she's just the first of her class.

But the one country that doesn't have much reason to worry is the United States, which has a significantly larger and more modern submarine force.

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