What would a U.S. Navy dream surface combatant look like? As with any tool, the answer depends on the job you have in mind for it. Will it fight for command of the sea, project power inland once the seas and skies are cleared of foes, or harass adversary fleets into impotence? Differently configured ships excel at different functions. The sizes, shapes and numbers of surface combatants, accordingly, should vary by the missions assigned. And unlike a handyman making repairs around your house, naval commanders have to worry not just about devising the right tool for the job, but also about opponents bent on foiling their plans. Try making household repairs under constant sniper fire.

Welcome to the sea fighter’s world. Now, naval enthusiasts and practitioners, including yours truly, tend to try to reduce ship design to whizbangs. We integrate the latest hardware into our ships and aircraft and assume it can cope with the threat. And there’s no gainsaying the importance of the technical dimension. Think about the mental games warlike youths play. My pals and I whiled away after-school hours dreaming up the ultimate warship, fighter aircraft, space cruiser, what have you. We stuffed weaponry, engines and armor into imaginary hulls and airframes with abandon—and no sense of limits.

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Girls? Fuggedaboutit. We were about martial glory! Kids have the luxury of inhabiting a dream world where resources are limitless and new technologies are improvised with ease. Indeed, the battlestar Galactica would represent the zenith of warship design in a world where money is no object and technical compromise is unnecessary.

Think about it. This spacefaring battleship/aircraft carrier was thickly armored. Her hull was rugged enough to withstand a nuclear blast—as it did. Nor were her defenses merely passive. Gunnery festooned her hull. Secondary batteries bristled around her flanks to pummel enemy fighters that came within reach. Main guns mounted in her prow blasted away during slugfests with rival dreadnoughts. And Galactica boasted a fighter air wing that could fan out, carrying the fight to foes of humanity.

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And if those aren’t virtues enough, she was quick. Equipped with faster-than-light drive, Galactica could slip out of a losing fight, reappearing light years away in an eyeblink, or mount a raid along an axis of her commanders’ choosing. So formidable were these capital ships that it took treachery—a computer virus insinuated into humanity’s defense network—to undo the battlestar fleet.

Why the excursion into sci-fi? Because Galactica illustrates what naval architects and shipwrights could accomplish if freed from limits on finances and technology—and thus shows how immutable these limits are in less carefree times. Like other ideals, then, the ultimate warship is an abstraction. It’s an ideal type that can be approached, but never reached.

All warships are products of compromise. The least suboptimal warship is the greatest warship. The three basic attributes of any man-of-war are speed, protection and armament. If naval leaders want lots of one attribute—say, hard-hitting armament—they typically have to forego part of the other two. Guns and ammunition weigh a lot, for instance. So does armor for withstanding enemy fire. That could set up a zero-sum competition between firepower and protection. Options narrow for fighting ships unable to take a pounding. You can be sunk or be crippled, or you can stay out of range.

That’s the lesson of the battlecruiser, a World War I ship type. Navies wanted both speed and firepower in a single hull, so they skimped on armor plating. That made sense for independent operations. The battlecruiser could rampage across the wine-dark sea, outgunning lighter craft or fleeing should it encounter an enemy task force. But commanders started using the battlecruiser like a battleship, a ship-of-the-line that boasted the same armament, but was sheathed in thicker armor. Using the battlecruiser with the battle fleet slowed her down, nullifying her chief advantage, while exposing her to battleship gunfire that could pierce her sides. This was a formula for failure.

And if you want firepower and protection—a ship that’s a heavy hitter, yet can take the best the opponent can dish out—it may cost you dearly in terms of speed. It takes a powerful, and pricey, engineering plant to drive a heavy hull through the water at high speed. Nuclear propulsion, anyone? Or you can satisfice, making do with adequate but less-than-optimal horsepower. Ships outfitted with cheaper plants can lumber along, perhaps getting the job done at slower speeds. That saves on up-front costs. But these savings hamper tactical and operational mobility. After all, a fleet advances only as fast as the slowest unit steaming in company.

Such are the quandaries confronting shipbuilders. Every desirable trait in a man-of-war comes with opportunity costs. Fantasies about omnipotent, invulnerable, ultra-quick ships—about ships constructed without give-and-take among their fighting qualities—are just that: fantasies. Which is why navies seldom hire teenagers to design ships.

Built-in speed, protection and armament are critical factors, to be sure. If a navy scants on such attributes, strategists and commanders may write checks naval hardware can’t cash. Sending forth fleets unable to withstand countermeasures the enemy throws at them does little good. Nevertheless, there’s more to fielding men-of-war than balancing among the factors that determine a ship’s performance as a machine. Operations and strategy unfold not in a vacuum, but in a competitive setting.

The ideal ship, that is, is fast enough, rugged enough and heavily armed to execute its mission at the decisive place and time—riding out or overpowering the defenses hurled at it by antagonists. No enemy is a potted plant. Opponents pit their strengths against American weaknesses in hopes of defeating U.S. Navy contingents, driving up the costs of operating off their shores, or deterring intervention altogether. Small wonder, say, Chinese strategists speak in terms of “counterintervention” measures, rather than access denial.

Whereas Galactica faced a cybernetic armada, the U.S. Navy faces the Chinas, Russias and Irans of the world. Putting the ultimate warship to sea, consequently, is also a matter of surveying the tactical environment, where the vessel must survive and thrive to accomplish the navy’s goals. Wise navies devise fighting ships for the settings where they’re likely to do battle, rather than build the ships they can and hope the fleet is equal to the rigors of particular combat theaters.

Which transports us back to the real world. Surface fleets of the familiar genus dating to World War II are concentric formations centered on “high-value units,” meaning aircraft carriers, amphibious transports or major surface combatants. Because the high-value unit is where the bulk of the force’s striking power resides, enemies can be expected to concentrate their efforts on taking it down. That’s why commanders surround it with outlying escorts, creating a thicket of defenses against surface, aerial or subsurface attack. A layered defense allows for multiple engagements against incoming threats. More shots fired boosts the probability of a kill—and thus of surviving to complete the mission.

For this old surface warrior (I served on the USS Wisconsin), it remains an open question whether traditional task forces have a future in hotly contested seas around the East and South Asian rimlands—in other words, in the waters and skies that matter. Fighting an enemy battle fleet on the open sea—as navies did in the days of sail—is one thing. But in this age of long-range precision weaponry, land power is an adjunct of sea power. Shore-based missiles, missile-toting warplanes and picket ships such as patrol craft and diesel-electric submarines are some implements local defenders can deploy to contest offshore seas and airspace. Fighting an enemy battle fleet, and air force, and army may be asking too much of any nautical force.

Surface navies, it appears, are becoming forces that stand into offshore zones only when sea and sky have been more or less scoured of threats. That implies that—perhaps unbeknownst to naval officials—the U.S. surface navy is undergoing a shift of missions. What might the greats say about this? For Sir Julian Corbett, the Jedi master of maritime historians, navies were made up of the battle fleet, which dueled enemy fleets for command of the sea; a swarm of inexpensive “cruisers” that fanned out to exercise command once the enemy fleet was put out of action; and a “flotilla” of lightly armed or unarmed craft to discharge mundane administrative functions.

Under normal circumstances, these arms of sea power did their work sequentially. Incapacitating or sinking the enemy main fleet eliminated the chief threat to sea command, letting cruisers and the flotilla do their jobs in more or less safe waters. But there was a catch. Corbett saw a “revolution beyond all previous experience” transpiring before his eyes, fully a century ago. As navies made the transition from sail to steam, they also fielded working torpedoes and subs and patrol boats to deliver these new munitions. All of a sudden, the flotilla acquired combat power vis-à-vis capital ships.