Around 500 fiber-optic undersea cables carry more than 95% of all internet data, strung like 19th-century telegraph cables under the oceans. On the afternoon of March 11th, 2011, Mitsuyoshi Hirai, the chief engineer of the cable maintenance ship Ocean Link, was sitting in his cabin 20 miles off Japan's eastern coast, completing the paperwork that comes at the end of every repair. Two weeks earlier, something — you rarely knew what —. Undersea cables, also known as submarine communications cables, are fiber-optic cables laid on the ocean floor and used to transmit data between continents. These cables are the backbone of the global internet, carrying the bulk of international communications, including email, webpages and video. As of 2026, we track more than 600 active and planned submarine cables. Lasers on one end fire at. Fiber-optic splicing is a task that demands extreme precision, typically carried out in the ship's cable control room. Engineers must fuse the tiny glass fibers with electric arcs, then encase the spliced section in protective material before lowering the cable back into the sea. Because undersea. James Stavridis is a Bloomberg Opinion columnist, a retired US Navy admiral, former supreme allied commander of NATO, and vice chairman at Carlyle.