THE U.S. NAVY is by far the most powerful naval force in the world, perhaps equal in combat power to all the rest of the world's navies combined. The U.S. Navy alone operates large deck, nuclear-powered aircraft carriers, their air groups (each more potent than most of the world's air forces) and their associated battle groups on a routine basis--and possesses no fewer than ten of these. The U.S. Navy alone operates a large force of nuclear-powered attack and ballistic missile submarines (the Soviet submarine force being but a shade of its former glory, while the Chinese submarine force is two or three technology generations behind). The U.S. Navy alone possesses the wherewithal to launch large amphibious assault operations. Most important of all, the U.S. Navy alone has the ability to project and sustain naval power at any point on the globe for weeks and months on end, thanks to its unsung but essential "fleet train" of oilers and underway replenishment vessels (In 1982, the British task force sent to the Falklands was literally falling apart for lack of maintenance by the end of that war).
The United States Navy today suffers from only one glaring shortcoming: a perceived lack of relevance. Navies traditionally exist to fight other navies, to preserve freedom of the seas, to control sea lanes, or at worst, deny them to other navies. But today the U.S. Navy is unchallenged. The Soviet Navy has trouble sending a relatively small task force into the Mediterranean after a year of preparation. The Chinese Navy seldom ventures beyond its bastion in the South China Sea. The rest of the world's navies are slouching into glorified coast guards. So why do we need a navy, and how does the Navy justify its shipbuilding budget?
The broad answer is deterrence. The existence of the Navy serves to inhibit potential aggressors from going to war by allowing the U.S. to project military power anywhere in the world, even where we do not have allies or bases in the theater. Thus, in any given crisis, every president since Eisenhower has always asked first, "Where are the carriers?" The size and power of the U.S. Navy inhibits most other countries from even attempting to match us at sea (even the USSR settled for a "sea denial" strategy intended to disrupt U.S. reinforcement of Europe for a limited period, rather than trying to wrest permanent control of the Atlantic from us), and so their options are immediately constrained by the existence of U.S. seapower.
In the Cold War, the U.S. Navy exercised this deterrent function in two ways: first, by maintaining the nuclear ballistic missile submarine force as one (and the most secure) leg of the nuclear triad; second, by developing and retaining the combat power to defeat the Soviet navy's aim of disrupting the Atlantic sea lanes. At a secondary level, the Navy also had the ability to strike along the periphery of the Soviet empire, and to intervene in secondary theaters or regional wars through airpower and amphibious assaults.
Today, these missions are gone, but the need for the Navy to act as a deterrent to aggression remains. The question is how.
The U.S. Navy recently tried to answer that question through a new policy document entitled "A Cooperative Strategy For 21st Century Sea Power." Produced and endorsed by the Navy, the Coast Guard, and the Marine Corps, it recognizes that the days of fleet actions are most likely over (barring a major conflict involving China), and that the future will be dominated by low intensity conflicts, humanitarian assistance, stabilization and reconstruction operations, and counter-terrorism operations. How does the Navy make itself relevant in that context?
The short answer is by continuing to be the United States Navy. With its large, general-purpose forces, the Navy is capable of a wide range of contingency operations without making substantial alterations to its force structure or its operational methods. The capabilities that support the Navy's primary military missions allow it to perform these low-intensity missions as well. This will become increasingly important given the rapid "littoralization" of the world's population--already a majority of people live within 60 miles of the ocean, and the shift from hinterlands to coast is accelerating.