Three hundred fifty ships is the answer. Now, what was the question?

President-elect Donald Trump has thrown his support behind calls from naval proponents to boost the U.S. Navy’s inventory of combat vessels from today’s 272 to 350. What purposes he has in mind for a brawnier navy are less clear. Will he pursue a strategy similar to President Barack Obama’s but more forcefully, will he scale back overseas commitments, or what?

The answer to that will determine whether 350 ships is the optimal size for the fleet.

Enunciated in 2014, the navy’s officially stated goal is 308 hulls. Three independent “fleet architecture” studies are revisiting that number, however. The Navy Staff, the Washington-based Center for Strategic and Budgetary Assessments, and the Mitre Corporation are surveying the strategic environment—the rise of China’s navy, an increasingly troublesome Russia, and on and on—and gauging how large a fleet it takes to handle such challenges.

It’s almost a foregone conclusion that the studies’ framers will conclude it takes more than 308 ships. The navy leadership agrees. On Friday the service released its much-anticipated “Force Structure Assessment,” espousing a 355-ship fleet. The leadership will review the fleet-architecture studies and, if necessary, refine the official tally for recommended ship numbers.

But what will the Trump administration do with a bulked-up U.S. Navy? Much has to do with the president-elect’s temperament and outlook on world affairs. On the campaign trail Donald Trump vowed to “make America great again” while putting “America first.” Good slogans, but not terribly actionable. The trick is to figure out what they mean for the navy in practical terms.

Acting on them could mean drawing down or reconfiguring the U.S. military’s peacetime presence overseas. Putting America first apparently involves convincing allies to assume more of the burden for their own defense. Trump has taken Europe to task in particular. In April, for instance, Trump reminded the Center for the National Interest, the publisher of this magazine, that only a small minority of NATO members spend 2 percent of GDP on defense.

There rest fall short of the alliance standard while the United States spends far more—and bears most of the load of allied defense. Why, asks the president-elect, should America care more about Western allies’ defense than the allies themselves do?

At the same time, though, Trump has pledged to rebuild the foundations of U.S. economic might, and thus the capacity to fund unrivaled armed forces. “Our military dominance,” he proclaimed, “must be unquestioned, and I mean unquestioned, by anybody and everybody.”

Taken together, such statements imply that the president-elect is sympathetic to “offshore balancing.” That’s the idea, commonplace on university campuses, that the United States should disentangle itself from power politics in the “rimlands” of Western Europe and East Asia as much as possible. America, say advocates of such strategies, should return in force only in times of dire peril—say, if a domineering power or alliance tries to conquer the rimlands and thence poses a threat to the Western Hemisphere.

Short of such mortal threats, offshore-balancing proponents would leave rimland nations to tend to their own defense. Let them balance the Chinas and Russias of the world so Americans don’t have to.

What does this imply about prospects for a 350-ship U.S. Navy? First consider the peacetime navy. There are many forms of offshore balancing, some less offshore than others. Trump’s words suggest that he may prove amenable to restoring a standing U.S. fleet presence in the Mediterranean Sea. Europeanists have been clamoring for Washington to return to the middle sea—and cancel the Obama administration’s “pivot” to the Western Pacific and Indian Ocean—almost since the administration announced the pivot in 2011. President Trump may heed their calls, and a 350-ship navy would furnish enough ships to do it.

That would constitute a sea change. Since the Cold War, the Mediterranean-based U.S. Sixth Fleet has shrunk from a serious fighting force centered on an aircraft-carrier task force to a command ship homeported in Gaeta, Italy, and four guided-missile destroyers at Rota, Spain. The destroyers, however, are assigned there as sentries to ward off ballistic-missile attack, presumably from Iran. This is not a force configured to do battle with the Russian Navy or other mischief-makers.

In a sense, then, the new administration’s maritime strategy could resemble a throwback to the Cold War. Restoring the Sixth Fleet to something resembling its former size and shape would reaffirm U.S. military supremacy. Yet guarding Europe from offshore would preserve Washington’s flexibility should NATO countries refuse American pleas to contribute more to the common defense.

After all, deployments can be canceled. Ships can be sent elsewhere or kept at home. Vigor would coexist with standoffishness in U.S. maritime strategy.

It’s also likely, given Trump’s America-first leanings, that ships would rotate through the Sixth Fleet from U.S. East Coast seaports rather than making the Mediterranean Sea their permanent home. Here too, the incoming administration could sustain America’s defense commitments for now—while signaling it will no longer tolerate free-riding from allies.

This would not be cheap. Shuttling vessels from North America rather than basing them in remote theaters is resource-intensive. Consider the arithmetic of forward deployment. It takes a bare minimum of three hulls—more for certain ship types—to keep one on foreign station. Such are the rigors of training, upkeep, and extended overhauls. Rotating ships from North America to the Mediterranean, then, would demand a substantial buildup of U.S. naval power.

How substantial? Congressional Research Service analyst Ron O’Rourke estimates that it would take about 42 U.S.-based vessels to reestablish a Mediterranean naval “hub.” That’s precisely the difference between the U.S. Navy’s 308-ship goal and the 350-ship figure cited by the Trump transition team. (The navy, notes O’Rourke, could accomplish the same thing with 14 extra ships if those ships were “forward-homeported” in Europe.) The Force Structure Assessment would allow for a larger Sixth Fleet, or provide surplus hulls to move around on the map as circumstances warrant. More options for statesmen and commanders is a good thing.

The geographic and fleet-allocation dimensions of peacetime strategy are worth monitoring as the new administration takes shape. Where forces go will reveal much about Washington’s priorities and worldview.

What about wartime strategy? Here the classics of strategy supply some guidance. Fin de siècle naval historian Alfred Thayer Mahan, for instance, explains how to size a fleet for combat: “a broad formula is that it 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....”

Take that Mahanian formula in reverse order. How can U.S. naval leaders estimate the largest force a prospective enemy is likely to send against the U.S. Navy in a particular theater? By asking what that foe wants at a given place and time, and how much it wants it. A rational adversary invests resources—ships, planes, armaments, seafarers’ lives—in an endeavor in proportion to the value it attaches to the political aims it hope to fulfill by undertaking that endeavor.

Less-than-crucial political aims, then, merit a partial investment of forces. No sane leader dispatches the entire military for a trifle. Sane leaders send detachments unless the mission is so critical that it warrants limitless expenditure of lives, hardware, and treasure—unless, say, national survival is at stake. Mahan urges strategists to undertake that political calculation, projecting what fraction of its naval power an antagonist may dispatch to a theater Americans care about.

That fraction becomes the yardstick for sizing a U.S. fleet. Wise strategists plan against the largest fleet an enemy may send—not against the enemy’s navy as a whole. Writing in the 1890s, Mahan calculated that the U.S. Navy could make itself supreme in the waters he cared about most—the Caribbean Sea and Gulf of Mexico—by constructing a modest fleet. It only needed to outmatch that part of Britain’s Royal Navy or Germany’s High Seas Fleet that London or Berlin would deploy to the Americas.

No open-ended naval arms race was necessary during Mahan’s lifetime to achieve local American supremacy. Nor is one necessary today.

Which leads to the second element in Mahan’s “broad formula”: a reasonable chance of success in battle. Martial strength is a product of material capability and human resolve and skill. The strong are both resolute and materially powerful. Fall short along either axis and strength suffers. Wise strategists take the measure of an opponent’s navy and their own. If the contending navies are comparable along the hardware and human axes, then superior numbers will make the difference in combat.

Asymmetries could skew the calculus one way or the other. A weaker but more numerous contender, for instance, might overcome a stronger yet outnumbered foe. It’s also worth recalling that we inhabit an age of land-based sea power. Land-based anti-ship and anti-air missiles, or missile-toting warplanes, can shape encounters that take place within their firing range as surely as shipboard weaponry can. Blithely excluding shore-based firepower from Mahanian calculations courts disaster—if the battle may take place under the shadow of enemy coasts.

And then there’s the final element in Mahan’s formula: making a force big enough to take to the sea and duel the most lethal foe likely to appear on the scene. In its imperial heyday, Great Britain sought to field a Royal Navy equal in numbers to its deadliest likely opponent. In Britain’s case, that meant constructing a fleet able to defeat the combined fleets of Bourbon powers Spain and France. Meet that numerical standard, and London could count on seamanship, tactical virtuosity, and élan—traits at which Jack Tar excelled—to tip the balance in action. British statesmen viewed the human factor as a difference-maker favoring the Royal Navy.

That’s one way to define a force strong enough to take to the high seas and fight with reasonable prospects of success. The Trump administration must devise its own. I would add a coda to Mahan’s formula: if in doubt, it’s better to deploy a surplus of power than risk having an enemy expose a deficit at a very bad time. Calculations can be wrong, an enemy more determined or skillful than prewar projections indicate. Trying to calibrate a battle force with just enough ships, planes, and seafarers to win risks a dismal showing.

So, Washington, refuse to yield to just-in-time thinking. Better an excess than a deficiency of force when death is on the line.

Administration officials can apply Mahan’s fleet-sizing formula to likely trouble spots around the world. One hopes they will. For example, what does Russia want in the Eastern Mediterranean, how much does it want it, and how large a fraction of the Russian Navy is it prepared to send to get it? There’s a rough-and-ready benchmark for the numbers and capability of a rejuvenated U.S. Sixth Fleet.

Or look at the China seas. What does China want in, say, the South China Sea, how much does it covet its goals, and how large a share of the People’s Liberation Army Navy is Beijing prepared to commit to obtain those goals? And there’s another wrinkle in China’s case: “anti-access/area-denial” weaponry. PLA commanders can back up the fleet with an array of shore-based firepower.

A Fortress China able to lob missiles scores if not hundreds offshore or dispatch warplanes from coastal airfields could skew the Trump administration’s Mahanian calculus toward greater numbers in the Western Pacific. China’s navy, then, is not the sole benchmark for U.S. naval adequacy vis-à-vis China. The benchmark is China’s navy—plus whatever land-based implements of Chinese sea power sport enough range to reach the scene of combat.

These are the sorts of calculations the incoming leadership must venture as it makes maritime strategy and constructs a navy to execute that strategy. Is 350 ships the right number? Is it enough to fend off challenges to freedom of the sea, succor allies when war looms, and scour the seven seas of brigands and gunrunners—all missions entrusted to the naval services?

The answer probably depends on which 350—or 355 if the navy gets its way—ships the administration opts to build. Congress and the administration could simply scale up the existing fleet proportionally, yielding a U.S. Navy that’s a larger version of its current self. In other words, aircraft carriers, cruisers, destroyers, submarines, and other ship types would make up about the same shares of the fleet as at present.

Or, the administration could redirect shipbuilding to favor certain ship types over others. It could bulk up the submarine fleet, for instance. It could fill out the inventory with small surface combatants to save money—albeit at the cost of thinning out the fleet’s aggregate fighting power. And on and on.

Combat power constitutes the common denominator between wartime and peacetime maritime strategy. A basic insight should inform fleet design in the coming years—namely that a fleet needs to make an impression. Ships are political implements as well as engines of war. The U.S. Navy’s ability to sway important audiences in peacetime, amplifying U.S. political influence, depends on how these audiences see the navy’s prospects for winning in wartime.

The U.S. Navy burnishes its good name, consequently, by burnishing its martial prowess. Only by making important audiences believers in its prowess can the navy deter prospective foes, reassure wavering allies and friends, attract new partners, and hearten constituents back home. Numbers and capability sufficient to win in battle are just as important in peacetime—when whoever most observers estimate would have won in action “wins” a peacetime showdown.

A final caution. As the Trump administration comes into being, it will be natural to look back to the United States’ last Republican-led naval buildup as the gold standard. The Reagan administration committed itself to a 600-ship U.S. Navy during the late Cold War, and devised a maritime strategy that instructed the navy to carry the fight to the Soviet Union all around the Soviet maritime periphery.

A triumphal afterglow still surrounds that age for American mariners. That’s the danger. We remember the 600-ship navy as some omnipresent, world-beating force that could sweep the sea clear of all comers. But bear in mind that the 600-ship fleet was the middling option—not the ideal one from a strategic standpoint.

The Reagan administration, that is, split the difference between a smaller navy predestined to lose and a bigger navy musclebound enough to engage the Soviet Navy, confident of victory, in all likely contingencies. Navy leaders wanted an 800-ship navy to guarantee success. They settled for a 600-ship navy that, in Mahanian parlance, enjoyed reasonable chances of success in most contingencies. Success, then, was not foreordained even had the navy reached that 600-ship plateau. (It didn’t, quite.)

The 600-ship navy, consequently, comprises a cautionary tale as much as an example to strive toward.

That’s the trouble with magic numbers in strategy: they obscure as much as they reveal. Let’s not make 350 or 355 a magic number. Indeed, a 350-ship fleet remains on the lean side considering the slate of missions entrusted to the U.S. Navy, and considering that the navy’s theater of operations spans the entire globe. Trump’s figure could be too high, too low, or about right.

Once again, it depends on what he expects the navy to do.

Setting and enforcing priorities is central to the art of strategy. It keeps ambitious ends in sync with the means available to fulfill them. A U.S. Navy with more hulls in the inventory could stage more robust forces in far-flung regions in peacetime. Extra numbers, moreover, would let the fleet prosecute its current slate of operations at a slower tempo, easing wear-and-tear on hardware and crews.

Better yet, more ships confers greater reserve strength should war erupt. A bigger force is a more resilient force. It can afford to lose ships in combat and fight on. Greater numbers of hulls, then, will pay dividends in war as well as peace.

More ships? Bring ’em on.

James Holmes is Professor of Strategy at the Naval War College, coauthor of Red Star over the Pacific, and a recent recipient of the Navy Meritorious Civilian Service Medal. The views voiced here are his alone.

Image: The guided-missile destroyer USS Zumwalt arrives at its new homeport in San Diego. Flickr/U.S. Navy