For the past five years or so these pixels have been arguing—nay, clamoring—for the U.S. Navy to build or buy a contingent of diesel attack submarines (SSKs) to fill out its undersea inventory. If anything the logic for going conventional is more compelling now than ever. It offers a way to add new hulls with dispatch, at manageable cost, and without imposing extra burdens on the few shipbuilders that specialize in naval nuclear propulsion. Best of all, a diesel contingent is an ideal implement for executing U.S. strategy in what the Pentagon terms its “priority theater,” bar none: the Indo-Pacific.

According to the Naval Sea Systems Command’s Report to Congress on the Long-Range Plan for Maintenance and Modernization of Naval Vessels for Fiscal Year 2020, the “Navy the Nation Needs” would number 355 vessels in all, up from 290 today. That tally includes a fleet of 66 nuclear-powered attack boats (SSNs). Today, according to the Naval Vessel Register, the figure stands at 50. The NVR lists 68 subs, but 18 of those are Ohio-class ballistic-missile or cruise-missile boats, not SSNs built for undersea knife fights.

Fifty is the number for now, but there’s downward pressure on that total. Los Angeles-class SSNs constructed to face the Soviet Navy are easing into retirement as they wear out, while shipyards are scrambling to introduce Virginia-class SSNs into service fast enough to replace them and, if all goes as planned, get ahead of the pace of retirements en route to that 66-boat force. Navy leaders fear builders may not keep up. In fact, some projections show the SSN count dropping into the low 40s by the late 2020s. Compounding the numbers challenge: the Ohio-class ballistic-missile submarines (SSBNs), which anchor the nation’s nuclear deterrent, are nearing the end of their service life at the same time as the Los Angeles class. Navy magnates have named replacing the Ohios with new-build Columbia-class SSBNs their top priority. 

Submarine construction priorities, in other words, pit two critical naval functions against each other—awarding nuclear deterrence precedence over command of the sea among the panoply of missions. That’s a reasonable call. Deterrence is a matter of national survival. SSBNs supply the invulnerable second-strike capability that has formed the beating heart of deterrence since the inception of the atomic age. But that strategic choice entails fearful opportunity costs. Wresting sea command from rivals such as China’s People’s Liberation Army Navy or the Russian Navy is an inescapable prerequisite for strategic success in the Indo-Pacific. Without free use of Western Pacific seaways in particular, Washington’s chances of facing down challengers and upholding solemn commitments to allies appear bleak. 

After all, forces that can’t reach the field of combat accomplish little. U.S. maritime strategy could be hollowed out if industry cannot keep up with the demand and the attack-boat fleet gets too lean to carry out its battle duty. Nuclear deterrence might hold fast, yet policymakers in Washington would have few options short of using doomsday weaponry if the U.S. Navy couldn’t count on using the maritime thoroughfare to rush reinforcements and supplies to scenes of action. Obstructing access would open up new strategic vistas for the Beijings and Moscows of the world. Few would believe the White House if it vowed to use nukes to, say, turn back aggression against the Senkaku Islands. No one risks Armageddon for the sake of unpopulated islets. Knowing U.S. leaders had no conventional recourse. Xi Jinping might roll the iron dice—and give the order. The same logic might apply for other hotspots along the Western Pacific rim—Taiwan, the South China Sea, you name it.

So what seems like a mundane tradeoff between ship types and budget lines turns out to be a tradeoff with fateful import for U.S. foreign policy. Pick one horn of the dilemma and the other gores you. To escape the dilemma let’s procure low-cost platforms in bulk to add mass and firepower to the fleet. Many more manufacturers work with conventional than nuclear propulsion plants, diversifying the number of potential suppliers. And it appears—using the Japanese Soryu-class diesel attack boat, acclaimed the finest sub of its type in the world, as the standard—that the navy could outfit itself with four or five conventional subs for the price of a Virginia. Or to avoid fratricide among submarine acquisitions, you could buy a Soryu equivalent for roughly the cost of a littoral combat ship that brings far less value to U.S. maritime strategy.

At this point the nuclear mafia within the silent service—the dominant faction among submariners, it must be said—will produce statistics beyond counting to prove that nuclear-powered craft are superior to their conventional brethren. And they will be right—by every measure except what matters. Namely, winning. The SSK is the right tool for the job provided it’s deployed at the right place on the map in the right manner to achieve maximum effect. Its true purpose: sea denial, meaning hampering foes’ freedom of movement through selected waterways.

Combining submarines with marine geography amplifies their efficacy at sea denial. Array diesel boats along, say, Asia’s first island chain in concert with unmanned combat vehicles, sea mines, surface patrol craft, warplanes, and missile-armed ground troops and you’ve erected a formidable barrier to passage between the China seas and Western Pacific. That’s a barrier that Beijing will think twice about flouting. You don’t need an SSN to stand picket duty, and in fact using it thus amounts to overkill. Nuclear attack boats have sea-control missions to perform on the open ocean. Used imaginatively, inexpensive diesel subs can reinforce conventional deterrence and free up precious SSNs for more important things, all without busting the shipbuilding budget. That’s the reciprocal of producing über-pricey SSBNs to reinforce nuclear deterrence. How’s that for cosmic balance?

Now, acquiring SSKs—preferably of a proven design in order to hold down risk and expense—charts an expedient path to strategic effectiveness. Should dollars and cents permit, however, fleet designers ought to experiment with more ambitious improvements to submersible technology and tactics. In a remarkable Naval War College Review article penned not long after the Cold War, Israeli naval officer Yedida Ya’ari lauds the submarine as a platform for littoral warfare. In fact, he implores navies to make better use of it along embattled coastlines.

The author points to the hazards near-shore battle holds for surface fleets along with subs’ relative immunity to those hazards. Littoral zones are cramped, dangerous places for surface warships. Complex terrain, short distances, and breakneck-speed hostile weaponry compress decision times for crews—tempting them to launch weapons in self-defense at the first hint of trouble. Littoral operations give new poignancy to the old saw he who hesitates is lost. In 1987, USS Stark suffered two Exocet missile strikes and 37 dead in the Persian Gulf when its crew failed to act. A year later USS Vincennes downed an Iranian Airbus over the Gulf when its skipper ordered missiles launched at short notice on incomplete targeting data. But there’s a curious cultural inversion. If surface sailors are on a hair trigger in confined quarters, submariners are trained to hide at the merest hint of detection. Roving sub-hunting aircraft are the usual culprits. The impulse to concealment handicaps subs’ combat effectiveness.

Admiral Ya’ari believes submariners can temper their defensive reflexes and bolster their efficacy by exploring new technology—anti-air technology in particular. Certainly the menace has not receded from littoral operations since the 1990s—just the reverse. Open-ocean combat, an arena ruled by nuclear-powered attack boats, poses fewer problems. Distances are longer, geography causes few problems, and shore-based weaponry is a tangential factor at most. Accordingly, to extrapolate from Ya’ari’s brief, outfitting SSKs destined for the littorals with newfangled technology should take precedence over equipping their nuclear-powered kin. These are the platforms that will stand into coastal waters to smite enemy surface, subsurface, and aerial traffic. Subs enjoy a kind of “bidimensional maneuverability” that permits them to evade the worst threats while landing heavy hits. SSKs are best suited to exploit that vertical maneuverability in sea-denial missions.

They’re cheap, defensible, and punch above their weight in the right setting—what’s not to love? 

James Holmes is J. C. Wylie Chair of Maritime Strategy at the U.S. Naval War College. The views voiced here are his alone.

Image: Wikimedia.