U.S. aircraft carriers are equipped with extensive active and passive defenses for defeating threats such as low-flying cruise missiles and hostile submarines. These include an array of high-performance sensors, radar-guided missiles and 20 mm Gatling guns that shoot 50 rounds per second. The carrier air wing of 60+ aircraft includes a squadron of early-warning radar planes that can detect approaching threats (including radar periscopes) over vast distances and helicopters equipped for anti-submarine, anti-surface and counter-mine warfare. All of the carrier's defensive sensors and weapons are netted together through an on-board command center for coordinated action against adversaries.

Large-deck, nuclear-powered aircraft carriers are the signature expression of American military power. No other combat system available to U.S. warfighters comes close to delivering so much offensive punch for months at a time without requiring land bases near the action. As a result, the ten carriers in the current fleet are in continuous demand from regional commanders -- so much so that extended overseas combat tours are becoming the norm.

Nobody really doubts the utility of large-deck carriers. There's nothing else like them, and the United States is the only nation that operates a fleet big enough to keep three or more carriers continuously deployed at all times. However, two issues have come up over and over again since the Cold War ended that have led at least some observers to question why carriers are the centerpiece of America's naval fleet. One concern is that they cost too much. The other is that they are vulnerable to attack.

The cost issue is a canard. It only costs a fraction of one-percent of the federal budget to build, operate and sustain all of the Navy's carriers -- and nobody has offered a credible alternative for accomplishing U.S. military objectives in their absence. Critics say carriers are more expensive than they seem because an accurate accounting would include the cost of their escort vessels, but the truth of the matter is that the Navy would need a lot more of those warships if it had to fight conflicts without carriers.

The vulnerability issue is harder to address because putting 5,000 sailors and six dozen high-performance aircraft on a $10 billion warship creates what military experts refer to as a very "lucrative" target. Taking one out would be a big achievement for America's enemies, and a big setback for America's military. However, the likelihood of any adversary actually achieving that without using nuclear weapons is pretty close to zero. It isn't going to happen, and here are five big reasons why.

Large-deck carriers are fast and resilient. Nimitz-class carriers of the type that dominate the current fleet, like the Ford-class carriers that will replace them, are the biggest warships ever built. They have 25 decks standing 250 feet in height, and displace 100,000 tons of water. With hundreds of watertight compartments and thousands of tons of armor, no conventional torpedo or mine is likely to cause serious damage. And because carriers are constantly moving when deployed at up to 35 miles per hour -- fast enough to outrun submarines -- finding and tracking them is difficult. Within 30 minutes after a sighting by enemies, the area within which a carrier might be operating has grown to 700 square miles; after 90 minutes, it has expanded to 6,000 square miles.

Carrier defenses are formidable. U.S. aircraft carriers are equipped with extensive active and passive defenses for defeating threats such as low-flying cruise missiles and hostile submarines. These include an array of high-performance sensors, radar-guided missiles and 20 mm Gatling guns that shoot 50 rounds per second. The carrier air wing of 60+ aircraft includes a squadron of early-warning radar planes that can detect approaching threats (including radar periscopes) over vast distances and helicopters equipped for anti-submarine, anti-surface and counter-mine warfare. All of the carrier's defensive sensors and weapons are netted together through an on-board command center for coordinated action against adversaries.

Carriers do not operate alone. Carriers typically deploy as part of a "carrier strike group" that includes multiple guided-missile warships equipped with the Aegis combat system. Aegis is the most advanced air and missile defense system in the world, capable of defeating every potential overhead threat including ballistic missiles. It is linked to other offensive and defensive systems on board U.S. surface combatants that can defeat submarines, surface ships and floating mines, or attack enemy sensors needed to guide attacking missiles. In combination with the carrier air wing, these warships can quickly degrade enemy systems used to track the strike group. Carrier strike groups often include one or more stealthy attack subs capable of defeating undersea and surface threats.

Navy tactics maximize survivability. Although U.S. aircraft carriers are protected by the most potent, multi-layered defensive shield ever conceived, they do not take chances when deployed near potential adversaries. Their operational tactics have evolved to minimize risk while still delivering the offensive punch that is their main reason for existing. For instance, a carrier will generally not operate in areas where mines might have been laid until the area has been thoroughly cleared. It will tend to stay in the open ocean rather than entering confined areas where approaching threats are hard to sort out from other local traffic. It will keep moving to complicate the targeting challenge for enemies. It will also use links to other joint assets from the seabed to low-earth orbit to achieve detailed situational awareness.

New technology is bolstering carrier defense. Although there has been much speculation about emerging threats to aircraft carriers, the Navy invests heavily in new offensive and defensive technologies aimed at countering such dangers. The most important advance of recent years has been the netting together of all naval assets in an area so that sensors and weapons can be used to maximum effect. Initiatives like the Naval Integrated Fire Control - Counter Air program link together every available combat system in a seamless, fast-reacting defensive screen that few adversaries can penetrate. Numerous other advances are being introduced, from the penetrating recon capabilities of stealthy fighters to shipboard jamming systems to advanced obscurants that confuse the guidance systems of homing missiles.

The bottom line on aircraft carrier survivability is that only a handful of countries can credibly pose a threat to America's most valuable warships, and short of using nuclear weapons none of those is likely to sink one. Although the Navy has changed it tactics to deal with the proliferation of fast anti-ship missiles and the growing military power of China in the Western Pacific, large-deck aircraft carriers remain among the most secure and useful combat systems in America's arsenal. With the unlimited range and flexibility afforded by nuclear propulsion, there are few places they can't go to enforce U.S. interests. And at the rate the Navy is investing in new warfighting technologies, that is likely to remain true for many decades to come.

Loren B. Thompson is Chief Operating Officer of the non-profit Lexington Institute and Chief Executive Officer of Source Associates, a for-profit consultancy. Prior to holding his present positions, he was Deputy Director of the Security Studies Program at Georgetown University and taught graduate-level courses in strategy, technology and media affairs at Georgetown. He has also taught at Harvard University’s Kennedy School of Government.

This first appeared in August of last year and is being reposted due to reader interest.