Explainer: How Vulnerable Are Undersea Cables That U.S. Says Russia Is Tracking?

Announcing fresh sanctions against Russia this week, the U.S. Treasury Department accused Moscow of "tracking undersea communications cables" and imposed punitive measures on a St. Petersburg firm that it says provided underwater diving equipment to Russia's Federal Security Service (FSB). "We are now seeing Russian underwater activity in the vicinity of undersea cables that I don't believe we have ever seen," U.S. Navy Rear Admiral Andrew Lennon, the commander of NATO's submarine forces, told The Washington Post in December. "It's not that it's much more difficult to sever cables in the deep ocean, it's just that the primary forms of interference are less likely to happen," writes Nicole Starosielski, an associate professor at New York University and author of the 2015 book The Undersea Network. "The sea is so big and the cables are so narrow, the probability isn't that high that you'd run across one," Starosielski adds.