In 2014, US warships spent about 210 days in the Black Sea. But two years after the coup, the number was down to 58.

The recent increase of US and NATO activity in the Black Sea is viewed as a major provocation in Moscow and was part of the reason why Russia sent more forces to its bases in western Russia and on the Black Sea in Crimea, what the West portrays as a troop buildup along Ukraine's border.

Still, defense pundits in think tanks tied to the US military establishment are arguing for a larger US naval presence in the Black Sea. Without it, they argue, "The result is an emboldened Russian President Vladimir Putin, who is orchestrating a stranglehold on Ukrainian ship traffic in the adjoining Sea of Azov and harassment of NATO ships in the Black Sea, said Foggo, now dean of the Arlington, Va.-based Center for Maritime Strategy."

"He and other analysts say that regardless of the outcome of the current situation in Ukraine, the U.S. must take the lead in developing a NATO Black Sea strategy," the report added.

Besides the naval presence, the US and its allies have also been deploying spy planes and bombers to fly over the Black Sea. Russian jets typically intercept the Western planes and escort them out of the area.