By MARK HELPRIN
WSJ.com

Last week, pirates attacked and executed four Americans in the Indian Ocean. We and the Europeans have endured literally thousands of attacks by the Somali pirates without taking the initiative against their vulnerable boats and bases even once. Such paralysis is but a symptom of a sickness that started some time ago.

The 1968 film, "2001: A Space Odyssey," suggested that in another 30 years commercial flights to the moon, extraterrestrial mining, and interplanetary voyages would be routine. Soon the United States would send multiple missions to the lunar surface, across which astronauts would speed in vehicles. If someone born before Kitty Hawk's first flight would shortly after retirement see men riding around the moon in an automobile, it was reasonable to assume that half again as much time would bring progress at a similarly dazzling rate.

It didn't work out that way. In his 1962 speech at Rice University, perhaps the high-water mark of both the American Century and recorded presidential eloquence, President Kennedy framed the challenge not only of going to the moon but of sustaining American exceptionalism and this country's leading position in the world. He was assassinated a little more than a year later, and in subsequent decades American confidence went south.

Not only have we lost our enthusiasm for the exploration of space, we have retreated on the seas. Up to 30 ships, the largest ever constructed, each capable of carrying 18,000 containers, will soon come off the ways in South Korea. Not only will we neither build, own, nor man them, they won't even call at our ports, which are not large enough to receive them. We are no longer exactly the gem of the ocean. Next in line for gratuitous abdication is our naval position.

Separated by the oceans from sources of raw materials in the Middle East, Africa, Australia and South America, and from markets and manufacture in Europe, East Asia and India, we are in effect an island nation. Because 95% and 90% respectively of U.S. and world foreign trade moves by sea, maritime interdiction is the quickest route to both the strangulation of any given nation and chaos in the international system. First Britain and then the U.S. have been the guarantors of the open oceans. The nature of this task demands a large blue-water fleet that simply cannot be abridged.

With the loss of a large number of important bases world-wide, if and when the U.S. projects military power it must do so most of the time from its own territory or the sea. Immune to political cross-currents, economically able to cover multiple areas, hypoallergenic to restive populations, and safe from insurgencies, the fleets are instruments of undeniable utility in support of allies and response to aggression. Forty percent of the world's population lives within range of modern naval gunfire, and more than two-thirds within easy reach of carrier aircraft. Nothing is better or safer than naval power and presence to preserve the often fragile reticence among nations, to protect American interests and those of our allies, and to prevent the wars attendant to imbalances of power and unrestrained adventurism.

And yet the fleet has been made to wither even in time of war. We have the smallest navy in almost a century, declining in the past 50 years to 286 from 1,000 principal combatants. Apologists may cite typical postwar diminutions, but the ongoing 17% reduction from 1998 to the present applies to a navy that unlike its wartime predecessors was not previously built up. These are reductions upon reductions. Nor can there be comfort in the fact that modern ships are more capable, for so are the ships of potential opponents. And even if the capacity of a whole navy could be packed into a small number of super ships, they could be in only a limited number of places at a time, and the loss of just a few of them would be catastrophic.

The overall effect of recent erosions is illustrated by the fact that 60 ships were commonly underway in America's seaward approaches in 1998, but today—despite opportunities for the infiltration of terrorists, the potential of weapons of mass destruction, and the ability of rogue nations to sea-launch intermediate and short-range ballistic missiles—there are only 20.

As China's navy rises and ours declines, not that far in the future the trajectories will cross. Rather than face this, we seduce ourselves with redefinitions such as the vogue concept that we can block with relative ease the straits through which the strategic materials upon which China depends must transit. But in one blink this would move us from the canonical British/American control of the sea to the insurgent model of lesser navies such as Germany's in World Wars I and II and the Soviet Union's in the Cold War. If we cast ourselves as insurgents, China will be driven even faster to construct a navy that can dominate the oceans, a complete reversal of fortune.

The United Sates Navy need not follow the Royal Navy into near oblivion. We have five times the population and almost six times the GDP of the U.K., and unlike Britain we were not exhausted by the great wars and their debt, and we neither depended upon an empire for our sway nor did we lose one.

Despite its necessity, deficit reduction is not the only or even the most important thing. Abdicating our more than half-century stabilizing role on the oceans, neglecting the military balance, and relinquishing a position we are fully capable of holding will bring tectonic realignments among nations—and ultimately more expense, bloodletting, and heartbreak than the most furious deficit hawk is capable of imagining. A technological nation with a GDP of $14 trillion can afford to build a fleet worthy of its past and sufficient to its future. Pity it if it does not.

Mr. Helprin, a senior fellow at the Claremont Institute, is the author of, among other works, "Winter's Tale" (Harcourt), "A Soldier of the Great War" (Harcourt) and, most recently, "Digital Barbarism" (HarperCollins).