Why ‘tapping’ a modern fiber-optic cable that lies on the seafloor is a lot harder than doing the same with a Cold War copper cable
During the Cold War, Russia and the U.S. built a number of submarines that were designed or later adapted to engage in spying activities on the seafloor. For the U.S. versions, these activities would often take the form of a submarine attaching itself to the ocean floor and tapping Soviet undersea cables.
The U.S. Navy built their seafloor spy machines at a time when it was relatively easy to tap such cables. During most of the Cold War, these cables were basically copper lines wrapped in protective rubber and plastic layers. These copper cables carried electrical pulses that were used as the propagation method for telegraph and telephone communications. The Soviets used these to connect their remote naval bases with their headquarters. Moscow considered such cable transmissions to be secure, in contrast to the highly non-secure nature of radio communications. For that reason the Soviets would usually not encrypt transmissions that passed through these cables, so by tapping them the U.S. could get a lot of information on enemy submarine operations and other military secrets.
Perhaps the most famous of the U.S. spy submarines was the U.S.S. Parche, a standard nuclear attack submarine launched in 1978. The Parche was later significantly refitted, including the addition of side thrusters and retractable under-boat skids that allowed the crew to maneuver it precisely and “land” it on the seafloor. The sub was also retrofitted with a large diver’s chamber on its back that connected to its aft escape hatch via a steel tube. It had all the amenities needed to serve saturation divers as they worked on the seafloor. Analysts also speculate that it had external lockers that housed tapping cables designed to tap undersea communication cables, which would be placed by the sub’s divers.
Nine years before the Parche was launched, the U.S. launched the much smaller NR-1. At a length of only 40 meters, the NR-1 was only a sixteenth the size of a regular nuclear submarine and was fitted with a very small nuclear reactor that took up most of the sub’s internal space. Also, whereas normal subs have nuclear reactor rooms that are wrapped in heavy radiation shielding, the NR-1 saved on weight and space by having only one radiation shield — that being the single wall that separated the small crew compartment from the much larger reactor room. Apart from being very cramped, the sub also gave its 11-man crew the thrill of sleeping with their feet pressed against the radiation shield that protected them from a nuclear reactor. This midget sub had a number of side thrusters that made it incredibly maneuverable. Unlike the Parche’s retractable skids, the NR-1 had two retractable truck wheels filled with alcohol that it used to drive around on the seafloor. The NR-1 didn’t have diver-supporting facilities but used a number of basic robotic arms to clamp onto things like Soviet undersea communication cables.
Apart from tapping enemy communication cables, spy submarines would also be used to find pieces of Russian missiles and other secret technologies on the seafloor. In 1976, the NR-1 was used to find and retrieve an F-14 jet and the classified U.S. missile it was carrying on the bottom of the Atlantic. The jet was swept off a U.S. carrier in a freak accident during a storm. Reality says: “Top Gun, kiss my ass.”
The first fiber-optic undersea cables were laid in the mid 1980s. Since then optical undersea cables have proliferated and today almost all of the 400 internet cables on the ocean floor are based on fiber-optic technology. It is unsure whether these new cables could physically be tapped by divers or a submarine, as it would require the spying team to somehow slice the cable in two (or at least fray the cable’s layers until the internal optic fibers are exposed) and insert a data-recording device that does not block the flow of light from one side of the severed fiber from reaching the other side of the severed fiber. Keep in mind that an optic fiber is as thin as a hair and these days undersea data cables have up to 24 and sometimes even 36 pairs of fiber strands.
Tapping such a cable on the seafloor would therefore seem like an impossible feat of micro-alignment, but in a way that is exactly what happens when a cable-repair ship repairs a broken cable, something that happens around twice a week somewhere on the planet. How exactly these repair ships manage to fuse together each broken strand of fiber is a story for another day, suffice to say they have to cut the cable in two while it is on the seafloor, then raise each side of the cable up separately. The damaged parts are then cut off and a long bridging section is then fused onto each side separately. This magical act of fusing dozens of strands of fibers together perfectly — so that light can flow through each strand smoothly — is done in a special room on board the ship, and the room looks like a high-tech lab. Needless to say, the act of fusing optic fibers would require highly trained technicians working with incredibly precise tools in a very special lab.
For these reasons it would be difficult for any nation’s navy to successfully tap a modern fiber-optic cable on the seafloor. The physics would be too challenging and there would be a long period where it would be obvious to the cable operator that something has cut the cable. This would be the period when any theoretical team of spy divers would have to cut the fibers before carefully placing a data-recording device in such a way that the fibers align perfectly on each side of the device. If such a device has indeed been invented yet, it would be awesome to behold.
Imagine my surprise then when I found an article that claims the U.S. does have a spy submarine that can do just that. The Associated Press reported in 2005 that the highly secretive U.S.S. Jimmy Carter had been upgraded to carry teams of technicians to the seafloor where they would purportedly be able to tap fiber-optic cables. Deutsche Welle reported in 2013 that such undersea tapping of optical cables by the Jimmy Carter would be unlikely and too “top secret” a kind of information for any journalist to verify independently. The German news outlet did however add that — if you were to try something that extraordinary — the best part of the cable to target would be the signal-amplifying “repeater” units that are built into the cable at intervals of around 80 kilometers. “At these spots, the fiber optics can be more easily tapped, because they are no longer bundled together, rather laid out individually,” Deutsche Welle reported.
The difficulty that would be involved in such a theoretical underwater tapping operation is perhaps why governments now put a high premium on not allowing their cable operators to have stretches where the cables cross over land that does not belong to the nation or an allied nation. Spy agencies can tap into fiber-optic cables that land on their territory with relative ease. Justin Sherman, a fellow at the Washington-based think tank called the Cyber Statecraft Initiative of the Atlantic Council, told Reuters that such cables are “a surveillance goldmine” for the intelligence agencies of the world. “When we talk about U.S.-China tech competition, when we talk about espionage and the capture of data, submarine cables are involved in every aspect of those rising geopolitical tensions,” Sherman said.
The Atlantic also reported in 2013 on how U.K. and U.S. spy agencies were in the habit of recording every single data bit that transits through the internet cables that pass over their soil.
This is the end of part 2 of our series on why China is planning to build its own private undersea cable network between itself, Europe, Africa and the Middle East. Part 3 will be published this Thursday and it will look at U.S. efforts to keep Chinese cable-laying companies out of modern cable projects, leading to China’s plan to build its own undersea network. We will also look at the vulnerabilities of undersea internet cables during wartime, and the type of warfare units that one would need to patrol and defend an undersea cable from tapping and sabotage.
Image: Petty Officer 1st Class Joshua Treadwell, Public Domain