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.