The Russian navy has begun trials of a nuclear-capable undersea drone that U.S. military officials believe could be used to stealthily target ports in major American cities. The Tass news agency, quoting unnamed sources, reported that testing of the Poseidon strategic drone, mentioned by Russian President Vladimir Putin during his state-of-the-nation address to both houses of Parliament earlier this year, was now underway. “In the sea area protected from a potential enemy’s reconnaissance means, the underwater trials of the nuclear propulsion unit of the Poseidon drone are underway,” the source told the news agency.