“Invisible Nuclear-Armed Submarines, or Transparent Oceans? Are Ballistic Missile Submarines Still the Best Deterrent for the United States?”, 2019-01-07 ():
The service lives of the US Navy’s 14 Ohio-class nuclear-powered, ballistic nuclear missile submarines (SSBNs), which make up the undersea leg of the country’s nuclear triad, are coming to an end while their replacements, the new Columbia-class subs, undergo research and development. This new SSBN is expected to cost about $128 billion to develop, leading critics to ask whether these investments make sense for a naval future where, because of advances in sensing technology, submarines may be harder to hide. Their point is a valid one to raise.
But the question whether submarines are getting harder to hide depends very much on whose submarines you’re talking about, who’s hunting them, and where.
To some degree, undersea geography is destiny, when it comes to hiding and finding nuclear submarines.
[Keywords: SSBN, nuclear-powered ballistic missile submarines, passive acoustics, reliable acoustic path, SOSUS, nuclear deterrence]
…The key technology underlying these assumptions of such an indelicate balance of terror was the SSBN, because unlike land-based forces it was considered survivable under all conceivable circumstances due to the fact that the oceans were essentially opaque. And indeed, this turned out to be case for the US’s SSBNs, but not for Soviet SSBNs.
A story that occurred behind then-high walls of secrecy explains why. Using narrow-band, low frequency, passive acoustic listening arrays that were developed during the 1950s and deployed all along the East Coast, the US Navy was able to continuously track the George Washington and then her 4 sisters as they crossed the Atlantic on their way to their first patrols in the Norwegian Sea. Rotating machinery within the hulls of the first 5 American SSBNs—such as reactor coolant pumps, turbo-generators, and reduction gears—created vibrations at specific low and very low frequencies. Little effort was made during their design to prevent these vibrations from coupling directly to the submarine’s hull and then to the water, generating specific, narrow-band acoustic tonals at low frequencies.
Beginning in the deep waters where the US Eastern continental shelf ends, and ending where the continental shelf begins in the Western approaches to Britain, these low frequency tonals propagated without important loss over the breadth of the entire North Atlantic.
The arrays that were collecting these tonals were part of what was soon to be a global network called the Sound Surveillance System, or SOSUS. By 1964, SOSUS or SOSUS-like systems provided ocean-wide, passive acoustic surveillance against any submarine that produced such tonals in the deep ocean basins of the North Atlantic and the Norwegian Sea, as well as in large parts of the Pacific… During the Cold War, the Soviet Union only learned of some but not all of the elements of this competition beginning in the late 1960s, and the Soviets did not deploy nuclear submarines designed from the start with quieting in mind until the Akula SSN in the early 1980s. Because of this, the USSR also got a late start in developing advanced, passive acoustic sensors. But most important, it did not even attempt to create a Soviet version of SOSUS in American SSBN deployment areas.
More than just sensor technology: This was not the result of any technological asymmetry; early SOSUS technology was not by any means out of reach of the Soviets. Instead it was the result of an asymmetry in the consequences of a common maritime geography. The deep sound channel, a propagation path that only occurred in deep water, is what enabled SOSUS.
SOSUS arrays therefore needed real estate that was reasonably near where the continental shelf ended and the deep ocean began, in order to bring cables deployed at the axis of the deep sound channel ashore to processing facilities where the data from the acoustic arrays could be processed and displayed. The United States had easy access to multiple such locations on its coasts and the coasts of its allies alongside the deep ocean basins that mattered in the Cold War, while the Soviet Union did not…Meanwhile, increasingly quiet American SSBNs disappeared from Soviet “view” as soon as they submerged on leaving port, only to reappear when they returned some 60 days later.
…The only submarines in the world that can know for sure whether they are immune to American anti-submarine warfare capabilities are American, and no countries other than the United States have the global presence and the full spectrum of anti-submarine warfare capabilities needed to make even very quiet submarines potentially vulnerable.
[Likewise, China is badly disadvantaged:]
…As with SOSUS during the Cold War, the key to undersea surveillance under modern conditions is a favorable maritime geography—and the maritime geography that the United States and China share in the Pacific greatly favors the US Navy.
The United States has distributed, bottom-mounted listening arrays that can detect any Chinese submarine attempting to pass through any of the exits from the Yellow, East, and South China Seas into the Philippine Sea and the greater Pacific. Meanwhile, the reverse is not true for China, either for American attack submarines entering China’s Inner Seas in the other direction, never mind American SSBNs deploying from their base in Washington to their nearby patrol areas.
The key technologies here are passive acoustic listening arrays that use what is called the Reliable Acoustic Path, or RAP (2007)…Unlike early SOSUS arrays, the Fixed, Distributed System uses very advanced technology for both sensing and signal processing. But like SOSUS, it depends on real estate for shore-based signal processing near where the continental shelf drops off into the deep ocean basin. In the Western Pacific, this real estate lies in what China calls the First Island Chain—meaning on the territory of US allies. Consequently, even if China could copy the Fixed, Distributed System or develop a version on its own (which is by no means guaranteed) deploying it at the entrances to its Inner Seas from the Philippine Sea would require fiber-optic cables spanning the entire East and South China Seas, whose shallow waters would make such cables impossible to protect either in peacetime or wartime.
As a result, the United States is likely to maintain undersea control of chokepoints like the Ryukyus and the Luzon Strait, with important consequences for the future of the Chinese SSBN force, not to mention its large force of modern, diesel attack submarines.