IT’S EASY to forget the virtues of submarines, which lurk beneath not only the waters but also the consciousness of most Americans. They aren’t as iconic as fighter jets or as visceral as tanks. But they can deny a stronger enemy navy control of important waters. Afterward they can exercise command of the sea, blockading or projecting power onto enemy shores with impunity. These elusive warships, in other words, pack an outsized punch.

Just ask Eugene Fluckey. Nicknamed “Lucky Fluckey,” the World War II submarine commander sent the most enemy tonnage to the ocean’s bottom of any skipper in the Pacific. Sinking Japanese tankers, freighters and other merchantmen dismembered a Japanese Empire reliant on sea transport. And raiding shipping was an option of first resort for Washington. U.S. Pacific Fleet submarines were able to start attacking Japanese shipping while American battleships were still burning in Pearl Harbor—long before the U.S. Navy surface fleet penetrated western Pacific waters. That’s what naval specialists call “sea denial.” It’s a strategy for hindering or preventing stronger adversaries from using certain nautical expanses.

Submarine operations spread progressively westward as the navy seized Pacific islands where forward bases could be built. Nearby bases let U.S. submariners establish a near-constant presence in Asian seas, sinking even more merchant shipping while pummeling the Imperial Japanese Navy from below. As the tide turned in the Pacific, undersea warfare made an indispensable contribution to American “command of the sea,” meaning near-total control of important sea areas.

And late in the war, Fluckey’s boat USS Barb took the fight directly to Japan, engaging in gun duels against Japanese shore sites. A landing party even went ashore to blow up a train. Such theatrics aside, Harvard professor Stephen Rosen maintains that a submarine blockade of Japan could have compelled Tokyo to surrender—even had President Harry Truman declined to order the atomic bombings of Hiroshima and Nagasaki. That’s high praise for these humble-looking ships of war.

Sea denial, sea command, the exploitation of command: submarine operations span the range of naval missions. Yet despite a century’s proof of submarines’ efficacy, from World War I in the Atlantic to the competition with China today, the classics of sea-power theory—the closest thing seafarers have to a how-to manual of naval combat—are puzzlingly silent on how to employ them in wartime or peacetime. The classics concentrate overwhelmingly on surface warfare, scanting undersea combat. It is high time to bring submarines into the canon.

 

AS AMERICAN submariners like to boast, some ships are built to submerge while others are made to submerge—once! There’s truth to that jest. First, these are warships that operate in three, not two, dimensions. In this sense they resemble combat aircraft, which can overfly surface fleets at altitudes of their choice. Adding that z-axis to submarines’ maneuvering space lets them operate not just near but also within the defensive perimeters around enemy formations. Think about the German U-boat lurking underneath a U.S. Navy destroyer in the World War II film The Enemy Below.

Surface vessels navigate across what amounts to a featureless plain, whereas submarines roam within a vast, three-dimensional column of water. This flexibility opens up tactical and operational vistas for submarine skippers that are unavailable to their surface brethren, whose ships lumber around in (mostly) plain sight. On the other hand, sub crews have to contend with terrain when operating in shallow water. Undersea warfare resembles land warfare in that sense. Soldiers work around mountains, valleys and defiles. Submariners must take account of the sea floor’s uneven if not shifting topography—in the near-shore environment in particular.

Second, concealment is a submarine’s chief method of defense. Surface-ship designers assume adversaries can detect, target and attack men-of-war plying the ocean’s surface. Such vessels must be stoutly built to absorb hits from enemy missiles or gunfire. They also boast elaborate active defenses—radar, antiaircraft and antiship missiles, electronic warfare—to ward off assault. The overriding assumption: ships exposed to enemy sensors will take hits.

By contrast, submariners go to extravagant lengths to hide. Loath to give away their presence—and thereby compromise their defenses—submariners typically operate their sonar sets in “passive” mode. They listen for telltale sounds emanating from enemy boats. Once they hear another ship’s engineering plant or other noise, they can identify, track and target it. This acoustic cat-and-mouse game works both ways. Running silent helps a boat evade detection. Slowing to a crawl quiets noise from the propulsion machinery.

Third, submarines are loners for the most part. Surface engagements are about concentrating firepower at decisive places on the map to overwhelm an opponent. Submarine warfare is about individual units hunting for action. Surface ships generally steam in concentric formations centered around “high-value units” such as aircraft carriers or amphibious transports. Outlying picket ships guard the high-value unit against surface, aerial or subsurface assault. A layered defense constitutes the carrier’s best chance of survival in a contested environment. Once in range, the formation projects offensive firepower against a hostile fleet or onto hostile shores.

By contrast, the submarine’s operating characteristics and need to remain unseen make independent operations its prime mode of action. Communicating with fellow boats increases the dangers of detection, as does operating in packs with them. Plus, passive detection represents a submarine’s best way to find adversary shipping. Passive sonar works best at low speeds, when the sub makes little noise of its own to obscure sounds emanating from an opponent. Sprinting short distances and pausing to listen is one tactic. Trailing a towed-array sonar—a “tail” festooned with hydrophones—behind the boat is another. A towed array lets crews hear minute sounds with even less interference from their own machinery.

While navies sometimes attach submarines to surface task groups, turning them loose in the depths remains the best way to prosecute undersea warfare. Freedom of action boosts an entrepreneurial crew’s chances of staying hidden, of finding enemy ships in the briny deep or on the surface, and of striking hard should circumstances warrant. Independence thus magnifies their combat potential. These disparities—technology, the radically different setting, this proclivity for stealth—add up to an approach to sea combat so different from surface warfare that it merits a fresh look. Sea-power theory schools judgment—and can improve the practice of undersea operations.

 

PERHAPS THE silence of the great works is less puzzling than it seems. Alfred Thayer Mahan (1840–1914) was the second president of the Naval War College and the author of The Influence of Sea Power upon History, 1660–1783, probably history’s most consequential treatise on maritime strategy. But his masterwork appeared long before submarines proved their mettle on oceanic battlefields. Mahan died in late 1914, after the guns of August rang out but before German U-boats commenced their rampage against Allied shipping. Mahan acknowledged the potential of submarine warfare in a vague way, yet never incorporated undersea combat into his theories.

Mahan’s contemporary, the English scholar Julian Corbett, likewise published his signature treatise before submarines reached their potential. His 1911 work Some Principles of Maritime Strategy drew primarily on the age of sail, which was the main fount of insights into naval war for fin de siècle historians. Corbett (1854–1922) was an adviser to Admiral Jacky Fisher, Great Britain’s top naval officer, who masterminded Royal Navy operations during World War I. But he, too, did not incorporate insights from the Great War. In short, history’s foremost naval historians perished just as undersea warfare started coming into its own. No theorist of comparable stature finished their work.

This oversight carries practical consequences. With few precepts to lift their gaze toward larger things, submariners find themselves consumed with engineering and administration. This is doubly true for the all-nuclear U.S. Navy submarine force. A Fluckey can make things up as he goes, and excel. Nevertheless, a more systematic approach to the subsurface domain is long overdue. What lessons might be extracted from the greats?

 

CORBETT LONGED for the age of sail. He longed in particular for the eighteenth century, when classifying warships was a straightforward matter. Clear purposes simplify the problem of designing and employing fleets to dispute, obtain or exercise command of the sea. A neat division of labor also makes things easier for analysts of maritime affairs. Let’s take Corbett’s basic precepts in turn.

First, there’s sea denial, whereby a lesser fleet contests a more powerful opponent’s preeminence. That’s where the U.S. Pacific Fleet found itself vis-à-vis the Imperial Japanese Navy in 1941–1942, with the Pearl Harbor fleet demolished and replacement ships still being built. Even the strongest force cannot be strong everywhere, at all times. Uneven superiority grants a weaker adversary a number of combatant options. By grouping assets, it can make itself superior at select points on the map despite its overall inferiority. Corbett notes that a savvy contender can mount “minor counterattacks,” small-scale assaults on soft spots in a dominant foe’s defenses.

Second, there’s command of the sea, sometimes termed “sea control.” Mahan defines command as “overbearing power on the sea which drives the enemy’s flag from it, or allows it to appear only as a fugitive.” For Corbett, as for Mahan, seizing command is the paramount goal of navies. To overpower an antagonist, statesmen and commanders can mass dispersed forces, order new ships built, court allies, or induce the adversary to disperse or waste his strength. The ultimate aim: a victorious counteroffensive. Disputing command—the sea-denial phase—is merely a precursor to winning command and its fruits.

Battle and blockade are the usual methods of imposing sea control. Dismantling an enemy force through battle represents the surest route to success. It eradicates serious opposition to one’s use of important waters, thereby yielding a permanent solution. Short of outright victory, a stronger fleet can confine a lesser one to port. Stationing superior forces offshore neutralizes an antagonist—but only as long as the cordon remains tight. Ships must linger offshore more or less indefinitely to enforce a maritime quarantine. Either way, one navy nullifies another—but blockades disperse strength, divert assets from enterprises promising operational and strategic gain, and leave open the possibility of an enemy breakout and a reversal of fortune. Blockades exact steep opportunity costs.

And third, navies covet command in order to exercise it. Battles are not—or shouldn’t be—fought for their own sake, but rather to advance the larger purposes of the war. Control of the sea, then, is an enabler. A navy that wrests command from its foes shields its homeland against an asymmetric counterattack. It can attack seaborne commerce, bringing economic pressure on an opponent to constrict its “national life.” It keeps its own maritime lifelines open. And it can attack, defend and support expeditionary operations, projecting force onto foreign territory in company with ground—and, today, air—forces.

This fundamental insight—that battle has larger purposes—is lost on mariners who see fighting as an end in itself. During World War I, for example, the Imperial German Navy assumed that the Royal Navy would steam into the North Sea for winner-take-all combat. Why? Because, German commanders believed, that’s what a navy steeped in the lore of Trafalgar did. Corbett, however, rejected habitual ways of thinking. Quoting maxims like “The enemy’s coast is our frontier,” he quipped, is like singing “Rule, Britannia!” to plan a campaign. Substituting formulas for original thought is no way to win. Nautical endeavors hinge on keeping policy and strategy in charge.

 

HOW DO navies execute these basic functions? Fleet design was central to Corbett’s account of maritime strategy. To trace the evolution of ship types and classes, he peered back to the founding of the Tudor navy by Henry VIII, whom he dubbed England’s “great sea-king.” In general, said Corbett, oceangoing navies could be divided into three categories: the battle fleet, cruisers and the flotilla. He saw a division of labor among the three. How do submarines fit into this scheme?

Battle fleets are made up of “capital ships,” major combatants meant to wrest supremacy from an enemy battle fleet. Capital ships combine offensive firepower with self-protection capable of withstanding the heaviest blows an enemy fleet can land. Cruisers are swarms of smaller, lighter combatants that police “permissive,” relatively safe expanses cleared of enemy fleets. Such craft are cheap in comparison with capital ships and can be built in large numbers—letting them disperse to many locations to regulate the flow of shipping. The flotilla is a hodgepodge of small craft, armed or unarmed, that performs the administrative tasks all seafaring states must carry out. Typically these are small, short-range, coastal vessels.

So much for what capital ships are. What do they do? Mahan fashions the best definition, describing them as “the backbone and real power of any navy,” ships that “by due proportion of defensive and offensive powers, are capable of taking and giving hard knocks” when battling peer fleets. For Mahan, as for Corbett, firepower and the ruggedness to absorb punishment set these heavy combatants apart.

Mahan enthrones capital ships—dreadnought battleships, in his day—atop a hierarchy of ship types. Vessels lacking such offensive and defensive power “are but subservient” to capital ships “and exist only for them.” How many heavy combatants does a navy need? “The answer—a broad formula—is that [the battle fleet] must be great enough to take the sea, and to fight, with reasonable chances of success, the largest force likely to be brought against it.”

There are political and risk-management dimensions to fleet design, then. Constructing a fleet demands that naval officials estimate the relative probability of threats. Mahan urged fleet architects to size and configure forces for the most likely actions they would confront. That is, they should build their navy to fight the battle it’s apt to fight, not to crush an entire enemy navy in some hypothetical engagement. If a rival appears ready to send its whole navy into a theater, then build against the whole navy. If its interests merit committing only a fraction of the navy, then build to counter that contingent. To do otherwise produces surplus capability at steep cost.

Mahan prophesied that a weaker U.S. Navy could outmatch the Royal Navy—the world’s premier seagoing force—in the Gulf of Mexico and Caribbean Sea. This was the theater that counted to Americans, both due to its proximity and because the Panama Canal would be dug there. Washington didn’t have to engage in an open-ended, ship-for-ship arms race in order to accomplish its goals to the south. The Royal Navy, in contrast, had worldwide commitments to uphold. British men-of-war were scattered throughout the seven seas, while the U.S. Navy could concentrate the bulk of its strength in the Gulf of Mexico and the Caribbean. America could amass local supremacy despite overall inferiority. Great Britain bowed to geostrategic logic around 1900. Its American squadron withdrew to home waters to compete with the German High Seas Fleet being built across the North Sea.

To devise a navy that fits the strategic surroundings, then, naval officials must take account of not just technology—propulsion, defensive protection, armaments—but also distance from likely scenes of action, the number and type of political commitments their own and rival nations have undertaken, and the likelihood and scope of conflict with potential antagonists. Strategic and political calculations—not just nuts and bolts—must be part of fleet design.

Assessing the strategic terrain is hard in any situation. But to make matters worse for naval planners, a “revolution beyond all previous experience,” to quote Corbett, had upended naval thought during the nineteenth and twentieth centuries. Sail propulsion gave way to steam, copper-sheathed wooden hulls to steel armor, smoothbore cannon to rifled guns firing explosive projectiles. Technological advances—in particular submarines, sea mines and self-propelled torpedoes—turned Corbett’s tidy fleet design upside down. Virtually any vessel could tote a mine or torpedo. Such weaponry empowered cruisers and the flotilla—the bottom dwellers in Mahan’s order of things—to strike heavy blows against battle fleets.

It was no longer easy to match ships with missions. Steam-driven men-of-war had fought few engagements for historians to plumb for insight. History no longer provided solid guidance. Still less could anyone foresee the exploits of a Eugene Fluckey plying the depths.

Suddenly, fleet commanders had to worry about screening heavy combatants against superempowered small craft. Torpedo boats and minelayers were beneath tacticians’ notice in the Mahanian hierarchy. But in this brave new world, laments Corbett, “the old practice is no longer a safe guide.” The best mariners can do is acknowledge that a technological revolution has taken place while distilling what guidance they can from history.

Gee-whiz weapons technology, then, had begotten “structureless” fleets. Technological ambiguity made it virtually impossible to design ships for specific functions. Corbett’s revolution never passed, as any contemporary seaman—including yours truly—will attest. The advent of nuclear-powered submarines, military aviation and guided antiship missiles only compounded the dilemmas Corbett bemoaned a century ago. Such is the state of sea-power theory in the twenty-first century.

Finding the submarine’s place in the menu of naval missions, then, is less simple than it appears. Are subs cruisers, or part of the flotilla? Or should they be seen as capital ships, the primary weapon of naval warfare? If the latter, naval establishments should draw up strategies centered on undersea warfare—and redirect scarce shipbuilding resources from pricey surface warships like aircraft carriers into submarine construction.

 

HOW DO submarines support traditional missions? First of all, they can help the weak defy the strong. A sea-denial fleet can redress its inferiority by massing existing forces at decisive places and times, constructing new assets or attracting allies willing to contribute to a combined force. Both Corbett and Mahan view disputing command as a transitory phase. Mahan exhorts naval commanders to seek decisive battle, while Corbett admits this is the correct approach “nine times out of ten.” Circumstances may compel the lesser power to bide its time while searching out opportunities to initiate a counteroffensive. Yet permanent control of vital waters is the ultimate aim for both theorists.

How should sub captains and squadron commanders use their boats? My purpose here is not to prescribe tactics. Nor was Corbett’s a century ago. Tactics and hardware are perishable, whereas strategic theory aspires to transcend changes in methods and technology. Still, a few points are worth raising. Nuclear propulsion, first of all, grants nuclear attack submarines (SSNs) the capacity to operate independently across vast distances, accompany surface task forces, operate in packs with other boats and otherwise contend for mastery of the waves. Used imaginatively, in short, nuclear-powered boats are ideal for maritime wars of positive aim.

Second, certain basic principles that Corbett spelled out endure. Questions of concentration and dispersal, for instance, appear timeless. Corbett urges commanders to disperse the fleet across as broad an area as possible, scouring vital expanses of opponents and protecting friendly shipping. They must do so while keeping ships close enough to one another that they can “condense” at the “strategical center.” This would be the site of battle should an antagonist agree to fight. Such “elastic concentration” permits a navy to police the sea while massing assets quickly to outmatch an opponent. Highly mobile ships like SSNs can spread out widely because they can rush to scenes of action, vectored in by intelligence, surveillance and reconnaissance assets.

But concentration is mainly about focusing firepower at decisive places rather than assembling large numbers of ships at point-blank range from one another. Accordingly, the firing ranges and accuracy of shipboard weaponry are crucial determinants of combat effectiveness. A submarine outfitted only with torpedoes must get much closer to targets than a missile-armed boat. Extreme firing range for a U.S. Navy Mark 48 heavyweight torpedo, for instance, is about twenty-seven nautical miles. (Effective firing range, at which the shooter stands an excellent chance of a hit, is shorter than this figure—in all likelihood much shorter.) By comparison, the navy’s Harpoon antiship missile—a missile of very modest reach by today’s standards—lets American SSNs engage targets over sixty nautical miles away. Doubling the combat radius quadruples the area covered by a weapon system. Simple geometry determines how far vessels can disperse while still bringing combat power to bear. Long-range precision ordnance thus helps fleets meet the demands of elastic concentration.

Third, it would be a mistake to draw too sharp a distinction between offense and defense, or between conventional and nuclear-powered submarines. Depending on the circumstances, any submarine can act either defensively or offensively. Indeed, Corbett observes that even offensive warfare has a pronounced defensive component. No force is strong enough to take the offensive everywhere, so offensive-minded strategists must mount an effective defense of weaker areas. Even defensive forces, moreover, should maintain an attitude of “alert expectation” in case the chance arises to strike an offensive tactical blow.

Both conventional and nuclear-powered boats, then, have parts to play in hybrid offensive-defensive warfare. If the maritime terrain permits, mixed fleets of diesel and nuclear-powered subs could prove ideal for seizing and holding critical sea areas. An apt division of labor would assign diesel boats the primarily defensive functions and nuclear attack boats the offensive ones. Conventional attack submarines (SSKs), for instance, can guard rear areas, shielding the homeland against seaborne assault while freeing SSNs to pursue operations in distant seas. As undersea capital ships, SSNs can help bottle up or defeat opponents close to their coasts—evening the balance before winning partial or complete control of the sea. If usable bases are among the fruits of victory, in turn, SSKs could forward-deploy to hold zones cleared by the battle fleet. Nearby logistical support would let them stage a forward tactical defense of gains won through strategic offense. Commanders should stay on the lookout for such inventive options.

 

EXPLOITING SEA control is the function to which submarines are least suited. Nevertheless, they have some part to play. Generally speaking, a navy must win command before exercising command. But what happens if an enemy navy refuses to fight? Or what if circumstances demand that a navy land troops or execute other missions before it controls the sea? Corbett observes that, in these cases, commanders may have to do things out of logical sequence. War, he says, is

not conducted by logic, and the order of proceeding which logic prescribes cannot always be adhered to in practice. We have seen how, owing to the special conditions of naval warfare, extraneous necessities intrude themselves, which make it inevitable that operations for exercising command should accompany as well as follow operations for securing command.

Navies, in other words, may have to use the sea before they control it. So long as an adversary declines to risk his fleet, he poses little menace. That allows cruisers—ships incapable of fighting capital ships but optimal for controlling permissive waters—to assume their central role in maritime strategy. They can raid enemy shipping from day one of a conflict, inflicting economic harm. Submarines are a natural platform for such guerre de course operations. Depending on logistics, SSKs may be able to hover off enemy ports or at focal points such as straits, intercepting enemy shipping. SSNs can do the same, or they can pursue merchantmen or warships. Subs of all types can distort enemy shipping patterns simply by making their presence known. Few mariners will approach a narrow sea knowing enemies skulk below. But detouring around undersea dangers costs time, fuel, and wear-and-tear on machinery and hulls.

Nor must submarines confine their efforts solely to enemy shipping. Cruise missile–armed subs, particularly SSNs, can use their armament to project power directly onto enemy shores. U.S. Navy SSNs were fitted with Tomahawk land-attack cruise missiles during the 1980s and fired on ground targets in Operation Desert Storm and ensuing campaigns. During the 1990s, the navy converted four Ohio-class submarines to carry Tomahawks. Redesignated SSGNs, or nuclear-powered guided-missile submarines, these boats number among the navy’s principal platforms for direct power projection. Or SSNs and SSGNs can act together. In Operation Odyssey Dawn in 2011, the SSNs USS Providence and Scranton joined the SSGN USS Florida in lofting cruise missiles against targets within Libya. And some SSNs and SSGNs are equipped to land special-operations forces along enemy coasts, supplementing power projection through covert means.

Submarines, then, offer potent capabilities both during and after the fight for sea control. When fitted with systems enabling them to project force onto land, they become truly maritime platforms. “Naval,” explains Corbett, is a subset of “maritime.” Why? Because “men live upon the land and not upon the sea.” Land is where great matters are decided. Accordingly, maritime strategy is the art of determining “the mutual relations of your army and navy in a plan of war.” It’s about dominating the land-sea interface, the natural preserve of sea power.

So maritime strategy isn’t all about navies. To be sure, winning, denying and exploiting command are about stifling enemy commerce and naval operations. But these functions also open avenues into coastal zones through which joint land/sea forces can shape terrestrial events. No longer can navies be partitioned cleanly into a battle fleet, a swarm of cruisers and the flotilla. SSKs fit most closely into the flotilla, SSNs into the battle fleet. But submarines defy easy classification. Their capabilities span all three domains while adding missions of which previous sea-power theorists could never have dreamed.

All this only adds to the need for commanders to use sea-power theory to unlock the full potential of structureless fleets—including their silent services. Imagine what a Lucky Fluckey versed in sea-power theory could accomplish today.

 

James Holmes is a professor of strategy at the Naval War College. The views presented here are his alone.