They were the workhorses of World War II in the Pacific, with fighter planes roaring off their pitching decks to pummel Japanese ships and soldiers.
Ever since, aircraft carriers have been a worldwide mainstay of American military might, moving into position whenever American forces, or those loyal to the United States, have been threatened.
But now, serious questions are being raised about their vulnerability in the 21st century. Has the age of the carriers ended? Or are they now invulnerable to destruction?
The question about this one class of ships is a pivotal one for White House and Pentagon officials as they craft a long-term vision for America's armed forces. They want to maintain US superiority in the skies, but tight budgets will likely mean tough choices.
The gray giants remain an important platform for projecting US power to the far reaches of the globe.
But even by Washington standards, carriers don't come cheap. A new, improved flat-top would run about $6 billion.
Moreover, in an era of smart bombs and unmanned surveillance planes, an aircraft carrier in combat puts roughly 3,000 US men and women at risk.
Although they are vulnerable to detection and attack, carriers at present "are also the most difficult warships to detect and attack," says longtime defense consultant Norman Polmar, the author of a coming book on the ships. For now, potential enemies lack sophisticated systems to track or seriously attack them.
"The real debate isn't whether vulnerability will occur. It's when it will occur," says Loren Thompson, the main author of a study on carrier vulnerability, yet to be released, by the Lexington Institute in Arlington, Va.
It's important that defense planners do their best to figure out the "when" of vulnerability as Secretary of Defense Donald Rumsfeld tries to identify what the future shape of the military should be. Among other things, he's trying to decide whether more big carriers should be built, or smaller ones instead. Or whether some other types of weapons should be phased in soon to replace some existing carriers.
For many, it may seem hard to think of today's gargantuan carriers as vulnerable. Each is as long as three football fields, as high as a 20-floor building, and carries a crew of 3,000. Most weigh 100,000 tons, much of it armor.
Several US carriers were sunk in the early years of World War II, but they had far less armor and defensive protection. Today's carriers "are so huge, and so sophisticated, that the entire Japanese fleet couldn't have sunk one," Mr. Thompson says.
Despite their bulk, they're relatively fast, churning through waters for months at their top speed of about 34 miles an hour, on a single supply of nuclear fuel. Being fast makes them hard for any current potential adversary to find, size notwithstanding, or to zero in on with attacking missiles.
Having lots of armor makes them hard to damage seriously . Various defensive systems, including a new communications system, are able to ward off attacks today by ballistic missiles, submarines, and mines, many experts say, and the Navy is working to thwart cruise-missile attacks.
"People exaggerate [carriers'] vulnerability and overestimate an enemy's capabilities," Thompson says. Potential foes who have missiles or nuclear weapons currently lack the sophisticated satellite tracking systems to hit a fast-moving target.
With future advances in protective weapons, today's carriers may be even less vulnerable in 10 or 20 years, Thompson adds.
But how vulnerable a carrier is in the years ahead may depend on where it sails. For instance, China is trying to develop systems that could be used to track and attack ships. Trying to sail an aircraft carrier off China's coast in 15 years, if that nation were an adversary, "could be difficult," says Robert Martinage, a specialist in future weapons at the Center for Strategic and Budgetary Assessments. Still, carriers will remain useful off the coasts of militarily weaker nations.
Still, some experts urge new concepts for replacing a few of today's carriers in 10 or more years. Mr. Martinage suggests developing smaller carriers that fire missiles rather than launching planes. And he recommends converting some submarines to fire a greater number of more-sophisticated missiles.
In the future, carriers will also likely face new threats. Already, cruise missiles are harder to see, and faster. Subs are quieter, can cruise undersea longer, and carry more lethal weapons.
"The big question," says Martinage, is "how fast are those ... going to mature, versus countermeasures we're working on?"
For now, carrier proponents point to the 1969 accident aboard the USS Enterprise, in which nine of its 500-pound bombs detonated. The force equalled half a dozen Russian cruise missiles, yet "the Enterprise could have resumed strike operations within hours," says the Lexington Institute's forthcoming study.
(c) Copyright 2001. The Christian Science Monitor