To Russia, the Yantar is an oceanic research vessel - to others, including the UK, it's a spy ship, and a worry for Britain's defence chiefs.
The vessel has long been suspected of secretly mapping out Britain's undersea cables, where more than 90% of our data, including billions of dollars of financial transactions, are transferred.
But now, a new escalation, with revelations the Yantar's sailors targeted Royal Air Force pilots in patrol planes with lasers.
Shining lasers into a pilot's eyes is provocative, and to use the Defence Secretary John Healey's words, "deeply dangerous". It's illegal in the UK and can lead to a prison sentence.
Healey's direct message to Russia and its leader Vladimir Putin was stark: "We see you. We know what you're doing. And if the Yantar travels south this week, we are ready."
