U.S. spy satellites, aircraft and submarines tracked the ship all the way down the coast to Cuba, according to two U.S. defense officials.
It had been years since the U.S. had seen this type of activity by the Russians, officials said. While the Russians have insisted the Yantar is not a spy ship, U.S. naval intelligence believes it has one significant and unsettling capability: small underwater vehicles that can cut vital undersea cables carrying vast amounts of commercial and military data, voice communications and Internet service between the U.S. and Europe.
Some of these details were first reported by the New York Times.
U.S. officials told CNN there was no indication that the Russians have any intention of cutting the cables, but they said that they are showing off their capability to U.S. naval intelligence by their actions.
It comes as the U.S. has watched for the last several months as Russian submarines in deep water have come close to the undersea cables. A classified network of Navy undersea sensors have been set off several times as the submarines approached the cables. The officials said the Russians would be aware in broad terms that their actions would cause the network to detect them.
The U.S. Navy considers all submarine operations to be highly classified and is almost always reluctant to talk about them. But earlier this month, the top U.S. Navy commander publicly addressed the rise in Russian submarine operations.
"The proficiency and operational tempo of the Russian submarine force is increasing," according to Adm. Mark Ferguson, Commander of U.S. Naval Force Europe.
"According to Russian Navy Chief Adm. Chirkov, the 'intensity' of Russian submarine patrols has risen by almost 50% over the last year," Ferguson told an audience in Washington.
Or as another Navy official put it to CNN: "Russian submarine deployments are through the roof."
Ferguson said Russia has increased the rate of operations to a level not seen in over decade.
He also pointed to Russian naval expansion in the Arctic and more than $2 billion in investment in the Black Sea fleet. They underscore what the U.S. Navy sees as a Russian military goal -- to broaden their naval operations and demonstrate a capability to control maritime areas during conflict.
"Russia has introduced new capabilities such as newer and more stealthy nuclear-powered attack and ballistic missile defense submarines. They are also expanding the reach of their conventional submarines with advanced cruise missiles," Ferguson said.
In September, the first Russian Kilo class submarine with a conventional Kaliber cruise missile moved from the North Sea to the Black Sea, bringing that weapon within range of Eastern Europe, according to the U.S. Navy.