More than 99 percent of international data flows through submarine telecommunications cables, according to the International Telecommunication Union (ITU). These fiber-optic lines carry everything from cloud traffic and financial transactions to video calls between continents. Much of that hidden infrastructure depends on a surprisingly specialized industry: manufacturers who build cables designed to operate for decades beneath the ocean.One of the companies building that infrastructure is SubCom, which operates a roughly 50-acre manufacturing campus in Newington, New Hampshire. The company designs, manufactures, and installs undersea fiber-optic networks, bringing together factory production, optical engineering, marine operations, and system testing.The facility is now expanding as demand for international bandwidth grows. But its work involves more than producing long lengths of cable: each system must be engineered to transmit data across thousands of kilometers while withstanding pressure, water exposure, and the physical stresses of installation on the seabed.How glass fibers carry data across oceansAt the heart of a submarine communications cable are optical fibers. These extremely thin glass strands transmit information as pulses of light. Unlike conventional electrical cables, which carry signals as electrical currents, fiber optics can carry enormous amounts of digital information over long distances with relatively little signal loss.However, the fibers cannot simply be dropped into the ocean unprotected. Submarine cables are engineered with layers that shield the delicate glass from water, mechanical stress, and other environmental hazards. Depending on the route, manufacturers can add protective layers and steel-wire armoring to help the cable withstand demanding conditions, particularly in shallower waters where anchors and fishing equipment pose greater risks.The cable’s construction also depends on its intended operating environment. A lightweight design may be suitable for deep ocean sections, while more heavily protected versions are used in areas where external damage is more likely. This means a single submarine network can use different cable designs along its route rather than relying on one uniform construction.Why a cable needs more than glassEven with high-quality optical fibers, signals weaken over long distances. Submarine networks therefore use optical repeaters installed along the cable route to amplify the signals, allowing information to continue across ocean basins.These repeaters must operate reliably in an environment that is difficult and expensive to access. Their housings need to withstand immense water pressure, prevent water ingress, and protect sensitive components. The cable itself also needs an electrical conductor to deliver power from shore-based equipment to repeaters along the route.At SubCom’s Newington campus, cable manufacturing is part of a larger integration process. The company says it builds the components of its subsea systems at the facility, bringing the cable, repeaters, and other equipment together before deployment. The completed system is tested before it is loaded onto a cable-laying vessel.That factory-to-ship workflow matters because installing a cable across an ocean is a major marine engineering operation. Teams survey the seabed, plan a route, account for water depth and potential hazards, and carefully control how the cable is laid. Near shore, cables are often buried for added protection, while sections in deeper water may rest directly on the seabed.A factory expanding for global data demandSubCom’s Newington facility has a history dating back to 1953, when it operated as Simplex Wire & Cable. Today, it is a central part of a company that says it has deployed more than one million kilometers (about 621,000 miles) of subsea cable systems worldwide, enough to circle the Earth roughly 25 times.The company is expanding the site to increase production. According to a January 2026 report in the Portsmouth Herald, based on information from SubCom, the Newington facility was producing approximately 58,000 kilometers (36,000 miles) of cable annually. The company aims to raise that figure to around 77,000 kilometers (47,800 miles) by the end of 2026, with a longer-term target of 100,000 kilometers (62,000 miles) per year. The expansion includes more than 100,000 square feet of manufacturing space, new extrusion and power-conductor lines, and plans to add 75 to 100 jobs at the site.That capacity is intended to serve a market shaped by growing data traffic, cloud computing, and technology companies connecting data centers across continents. SubCom has worked on systems including Grace Hopper, which connects the United States, United Kingdom, and Spain, and SEA-ME-WE 6, a 19,200-kilometer (11,900 miles) network linking Southeast Asia, the Middle East, and Western Europe.Submarine cables remain vulnerable to anchors, fishing activity, seabed disturbances, and natural hazards, making careful route planning, maintenance, and repair essential. The ITU has highlighted the need to strengthen the resilience of these networks as they underpin international communications and economic activity.The result is an often-overlooked part of the internet’s physical infrastructure. Data may appear to travel invisibly between screens, but much of it depends on glass fibers manufactured in specialized facilities, assembled into pressure-resistant cables, tested on land, and laid across the ocean floor. In Newington, that work is becoming an even larger industrial operation as the world’s demand for international connectivity continues to grow.