Word has it that China’s People’s Liberation Army Navy (PLA Navy) has staged a breakthrough in submarine propulsion. At any rate, that’s the word from marine engineer Rear Admiral Ma Weiming, a specialist in electromagnetic systems. Admiral Ma recently reported on state-run CCTV that shipwrights are installing shaftless rim-driven pumpjets in China’s “next-generation nuclear submarines,” meaning attack or ballistic-missile boats. (Click here for a layman’s description of pumpjet technology.) Ma crowed that Chinese engineers are “now way ahead of the United States, which has also been developing similar technology.”

If Admiral Ma is playing it straight—rather than hyping promising but yet-to-be-proven gadgetry—then the PLA Navy is poised to overcome a technological and tactical defect that has plagued it since its founding. American submariners long lampooned Soviet and Chinese nuclear boats for being noisy and easy to detect. PLA Navy boats remained backward long after the Cold War. Ultraquiet propulsion, though, would put an end to unquestioned U.S. acoustic supremacy, opening up new operational and strategic vistas before the PLA Navy while ushering in a deadlier phase of U.S.-China strategic competition.

The rim-driven pumpjet is an electrically driven “propulsor” that simplifies and thus quiets an engineering plant. Older technology typically uses gears to connect the elements of a drive train. Steam spins the innards of high-speed turbines. Turbines spin far too fast for any main propulsion shaft or propeller, however, so ships outfitted with traditional engineering plants have “main reduction gears” that step down the speed of rotation drastically, to speeds useful for the shaft that turns the screw and impels the hull through the water. Gears are noisemakers. Pumpjet technology dispenses with them, simplifying and silencing plant operations.

The design also reduces cavitation—bubbles churned up when a propeller turns rapidly underwater, leaving low-pressure zones behind the blades where water can boil. Cavitation emits noise that enemy sonar operators may hear. Thus it can alert hostile anti-submarine-warfare (ASW) forces, helping them find, track and target the emitter. Hence the allure of novel technology that suppresses cavitation.

Now, there are ample grounds for skepticism toward Admiral Ma’s claims. New technology remains a hypothesis until tested out in real-world operations. But at the same time it’s doubtful Ma was simply showboating for Chinese TV viewers. Rising competitors have caught up with established navies before, or even leapfrogged them in certain areas. The Imperial Japanese Navy defied expectations, devising the Long Lance torpedo that it deployed to devastating effect at Pearl Harbor. The Soviet Navy concocted antiship missiles and torpedoes that give the U.S. Navy fits to this day. Thus it behooves us to ask what if: what if China pulls off a technological leap of similar magnitude?

Set aside the question of whose submarines are quieter than whose. Boastfulness—the urge to be the biggest, best and most of everything, and to have others acknowledge it—forms a strand in China’s cultural DNA. Ma is indulging in it. But no one is going to hold a contest to measure noise given off by U.S. Navy and PLA Navy boats, and award victory to the quietest fleet. Combat is the true arbiter of military effectiveness—and undersea combat hinges on whether “hiders” or “finders” prevail. It pits a sub’s capacity for silent running against the acuity of ASW sensors and operators trying to ferret it out.

In other words, if American hiders remain quiet enough to evade Chinese finders, they hold the advantage of stealth. If acoustics has befriended the PLA Navy, then American finders have a problem. And if both submarine services can elude ASW hunters, then both they and surface fleets are in dire peril. “Peer” submarines could engage one another at close proximity in the deep, or strike against surface vessels without warning. Indeed, the surface of embattled oceans could verge on no-go territory. That prospect makes this thought experiment about the future of subsurface warfare worthwhile.

Suppose rim-driven pumpjet propulsors do pan out for China’s navy. How might commanders use newly elusive boats? First of all, they might afford nuclear-powered ballistic-missile submarines (SSBNs, known to U.S. submariners as “boomers”) precedence when installing newfangled propulsion hardware. The PLA Navy already operates a sizable fleet of diesel-electric attack subs that satisfices for antiaccess/area-denial purposes. They can make shift until silent-running nuclear-powered attack subs (SSNs) join the fleet. SSNs can wait. By contrast, the navy stands at the brink of fielding its first effective SSBNs.

Fabricating a new capability would seem to take precedence over improving an old but adequate one—especially if the nation’s nuclear deterrent depends on the new capability. If this logic prevails, how will the PLA Navy employ working boomers? To all appearances, it envisions employing the South China Sea as an offshore “bastion” for SSBNs, much as the Soviet Navy of yesteryear made semienclosed waters into protected bastions for its missile boats. Undersea deterrence, then, probably numbers among the motives impelling the PLA to transform rocks and atolls into fortified outposts, acquaint itself with underwater hydrography, and so forth. China’s Type 094 SSBNs or their pumpjet-equipped descendants could slip out of the sub base on Hainan Island, descend into South China Sea waters, lose themselves in the depths and dare rival navies to come into China’s “near seas”—expanses that fall under the shadow of land-based PLA missiles and aircraft—to hunt them.

Or if Chinese Communist Party leaders feel comfortable granting SSBN skippers the liberty to venture outside the near seas (though that’s a lot of atomic firepower to entrust to a naval officer whose loyalties might prove suspect), the Luzon Strait affords a convenient entryway to the western Pacific. Within the strait lies the Bashi Channel, a deep underwater thoroughfare into the Pacific. The weather between Luzon and the southern tip of Taiwan often works against airborne ASW; subs transiting the channel can conceal their whereabouts by diving beneath thermal layers that play tricks with sound. An ultraquiet SSBN, in short, could thrive in South China Sea patrol grounds—and beyond.

Second, PLA Navy commanders doubtless salivate at the prospect of ultraquiet attack boats. They could merge new SSNs—presumably the Type 095s under development—into their antiaccess defenses against the U.S. Pacific Fleet. They could package new with old units inventively. For example, they could station a picket line of diesel boats and older Type 093 SSNs along likely axes of approach from Hawaii or U.S. West Coast seaports. Speedy but quiet Type 095s could act as “skirmishers,” operating forward of the pickets. SSNs could snipe at the Pacific Fleet’s flanks during its westward voyage while scouting for the rest of the fleet, and for shore-based PLA defenders. They could mount piecemeal attacks against the American fleet, or even try to herd it toward the picket line for additional punishment.

PLA commanders thus could use ultramodern platforms to wring new value out of legacy platforms. Such an approach would harness the latest technology while staying true to China’s Maoist tradition of “active defense.” Active defense—which, as Chinese military folk remind us, remains the “essence” of Chinese military strategy decades after Mao Zedong’s demise—envisions luring foes deep into Chinese-held territory. PLA defenders stage tactical actions to weary enemies as they come. They fall on isolated units and try to smash them. Successive small-scale attacks enfeeble enemy forces, setting the stage for decisive battle on Chinese ground.

Think about the options that may become available to Chinese skippers as propulsor technology matures. Diesel boats could act as western Pacific pickets, or congregate in wolfpacks to concentrate firepower from multiple axes. Relatively noisy Type 093s could act as decoys, distracting American ASW hunters while Type 095s spring ambushes at opportune moments. And on and on. Commanders could combine and recombine forces in limitless ways—in keeping with China’s way of war.

Call it undersea active defense.

Third, the advent of quiet-running SSNs would let the PLA Navy play submarine-on-submarine games reminiscent of those once played by U.S. and Soviet boats. To date, lacking a peer to U.S. Navy Los Angeles– or Virginia-class SSNs, the PLA Navy has employed its submarine fleet mainly as an antisurface force. It waits offshore for hostile forces to approach, then does its best to pummel them with missiles or torpedoes. American submariners, by contrast, will tell you the best ASW weapon is another submarine. They view hunting subs as their chief contribution to high-seas warfare. Chinese submariners might follow suit if their boats ran quiet enough, and boasted sensors sensitive enough, to make sub-on-sub ASW an option. Or they might incorporate ASW into their operational portfolio while retaining the emphasis on antiship missions.

Either way, PLA submarine operations would take on an intensely offensive hue. No longer would the sub force be a mostly static force lofting antiship missiles toward adversary surface task forces. It would seek out adversary subs as well—and, if successful, project China’s antiaccess defenses into the depths in a serious way for the first time. No longer could the United States’ silent service prowl Asian waters with impunity. Indeed, if both fleets were comparable in stealth, cat-and-mouse games might predominate. This would be a dangerous business. Reaction times would be minimal if boats could only detect and track one another at intimate range. Proximity would magnify the prospect of collisions, accidents of other types, or even inadvertent exchanges of fire. Both navies and their political masters must think ahead about how to manage close-quarters encounters in the deep.