In March, Russian state-owned media outlets made a surprising announcement: a new documentary series had entered into production that promised to tell the story of Russian nuclear attack submarine commanders sneaking their vessels into American harbors. The story wasn’t set in some fictional “Hunt for Red October”-esque scenario, however — according to the Russians, the series would depict real events from the recent past.

The commander of the submarine squadron, Sergey Starshinov, was quoted by the Russian-owned RT as saying that the submarines were tasked with coming to within 12 nautical miles of multiple American Navy bases along the East Coast, loitering and gathering intelligence, and then departing all while avoiding detection from American sea-based defenses. That 12 nautical mile figure, while likely not true, was an important element of the story from a foreign policy perspective, of course, because it’s generally held that international waters begin at the 12 nautical mile mark. In other words, despite Russia’s decision to use American defenses as a test run for their stealthy subs, they didn’t want to allow their announced success to be held against them diplomatically.

The United States, which is rapidly developing a number of new submarine detecting technologies, opted not to publicly address the claims made by the Russian Navy, and with good reason: if American forces had detected the submarines during their approach, the U.S. government couldn’t admit it without also revealing at least some details about the manner in which they did, potentially offering Russia the sort of constructive criticism they need to counter U.S. defenses next time. Then, there’s the other possibility — that the United States failed to detect the encroaching submarines at all.

Of course, it stands to reason that the entire show and accompanying coverage were just elements of Russia’s constant disinformation and propaganda efforts, but as time wore on, it began to seem like the U.S. Navy had reason to take the Russian claims seriously. That reason was likely the serious increase in Russian submarine activity all throughout the North Atlantic in recent months. In fact, Russian subs have been so busy beneath the surface of the Atlantic that Chief of Naval Operations Adm. John Richardson recently characterized it as the biggest influx of Russian submarines in that region in at least a quarter century.

Perhaps the most telling response the U.S. Navy has made in the months since Russia’s announcement has been the decision to bring the U.S. Navy’s 2nd Fleet back from retirement. The force, which found its way onto the chopping block in 2011 in favor of freeing up capital for acquisitions, has historically been tasked with policing the North Atlantic and defending America’s eastern seaboard — an issue of increasing importance amidst the recent large uptick in Russian submarine activity, but they’re not the only threats now actively operating in the waters abutting America’s most populated coastline. According to Richardson, the People’s Liberation Army-Navy out of China is also making its presences known in the 2nd Fleet’s stomping grounds.

“They’re certainly a pacing competition for us in terms of the naval threat,” he told VOA, calling the Chinese Navy “global” and clarifying that China’s naval forces can operate anywhere in the world that Beijing wants. This statement runs counter to the generally accepted perspective that China’s Navy while growing rapidly in capability, remains a “green water” fleet — meaning that its forces are primarily beholden to staying near enough to Chinese shores to return and refuel with regularity. China’s expanding fleet of aircraft carriers, for instance, appear to represent a significant technological leap for the nation, but still rely on diesel-electric engines for propulsion — unlike America’s truly global fleet of nuclear powered Nimitz and Ford class carriers.

However, although carriers are often recognized as the premier ships of any fleet, it’s China’s nuclear submarines, not carriers, that possess the ability to operate thousands of miles from friendly waters. China’s decision to begin operating attack submarines in the Atlantic and even the Mediterranean Sea create what Richardson referred to as a “new dynamic” to American defense.

The threat posed by these submarines hailing from current diplomatic opponents is broader than concerns about a World War III inciting attack — many experts have levied concerns about Russian interference with the undersea cables linking Europe and North America. Severing these lines (or infiltrating them) could have far-reaching ramifications on communications and economics for a large portion of the world’s economy. Further, positioning nuclear missile equipped submarines near to America’s coast creates an additional dynamic to contend with in the ever-evolving competition that is mutually assured destruction (MAD). America has the oldest and potentially least capable nuclear arsenal of these three nations, and MAD only truly works when nuclear powers are balanced enough to ensure the “mutual” portion of MAD is a certainty.