In August, China launched two ballistic missiles that, according to a Chinese military expert, hit a moving target ship in the South China Sea thousands of miles from their launch sites.

If true, the test - which came a month after the US deployed two carrier strike groups to the region and a day after a US U-2 spy plane observed a Chinese navy live-fire drill - is the first known demonstration of China's long-range anti-ship ballistic missiles against a moving target.

"We are doing this because of their provocation," Wang Xiangsui, a former Chinese colonel and professor at Beijing's Beihang University, reportedly said in reference to the deployments, calling the test "a warning to the US."

Not to be outdone, the Russian navy conducted its third test launch of the Zircon hypersonic anti-ship cruise missile in the White Sea in December. Launched from a frigate, the missile reached a speed of Mach 8 before hitting a "coastal target" more than 200 miles away.

The tests are just the latest indication that American aircraft carriers, long viewed as kings of the seas, may soon face a real threat to their existence.

High-priority targets

America's carriers have always been among the biggest targets for rivals. While the Soviets publicly lambasted carriers as "the oppressor of national liberation movements," they recognized them as a dominant weapon platform.

This was especially the case after they realized US carrier air wings included aircraft carrying nuclear payloads.

Declassified CIA documents reveal that by the 1980s, the Soviets rarely criticized carriers in internal discussions and even praised them for providing "high combat stability." One document from 1979 stated that carriers would be "the highest priority in anti-ship attacks" in potential war scenarios, with amphibious assault ships probably close behind.

Plans to deal with carriers were based almost entirely on anti-ship cruise missiles fired from submarines, bombers, and surface ships - ideally all at once. To that end, the Soviet navy emphasized cruise missile technology and missile-carrying capacity on all of its vessels - even on its own aircraft carriers.

Soviet navy Tu-16, Tu-95, and Tu-22 bombers were the primary aerial delivery systems. Cruisers of the Kynda, Kresta, Slava, and nuclear-powered Kirov classes were the primary surface delivery platforms.

A host of nuclear-powered and diesel-electric submarines, like the Oscar II- and Juliett-class, would fire those missiles from underwater and on the surface.

But even this may not have been enough. US carrier defenses and air wings were deemed so strong by the Soviets that as many as 100 bombers would be sent to attack one carrier, with losses expected to be as high as 50%. Soviet pilots weren't even given detailed flight paths for their return.

It was also feared that the missiles could be shot down or intercepted, so the Soviets concluded that many had to be armed with nuclear warheads.

Waning carrier dominance

With the Cold War over and the Soviet Union gone, American carrier dominance seemed more than assured. Those carriers have played key roles in conflicts the US has been involved in since the 1990s.

But the post-Cold War order is slowly being challenged - mainly by China's meteoric rise in military power, which has implications for the carrier's dominance.

American carriers are among Beijing's biggest concerns. Their presence helped deter an invasion of Taiwan in the 1950s, and in 1996 two carrier battlegroups embarrassed China by operating freely around Taiwan during a period of heightened tensions, forcing Beijing to recognize US military power.

Since then, China has invested heavily in anti-carrier capabilities. It first bought a slew of weapons from Russia, including Su-30MKK multirole fighters, 12 Kilo-class attack submarines, and four Sovremenny-class guided-missile destroyers.

But missiles have been China's main focus. It has amassed one of the world's largest and most advanced missile arsenals, 95% of which falls outside the limits of the Intermediate-range Nuclear Forces Treaty, which prohibited the US and Russia from having missiles with ranges between 310 miles and 3,100 miles. The US recently withdrew from the treaty, and China was never party to it.

The two missiles tested in August were variants of the DF-21 and DF-26, which have ranges up to 1,300 and 2,400 miles respectively.

Flying higher, faster, and farther than Soviet cruise missiles, China's anti-ship ballistic missiles could overwhelm the anti-missile defenses of a carrier and its escorts, and force the carrier to stay far enough away to render its air wing useless.

A US Defense Department report released this year stated that China's missile development was one area in which Beijing has "achieved parity with - or even exceeded - the United States."

New threats

Able to fly at speeds over Mach 5 (over 3,800 mph), hypersonic missiles are too fast for anti-missile defenses to respond effectively. They can also change direction mid-flight, making it virtually impossible to intercept them.

China has two hypersonic weapons in service: the DF-17, and the DF-100. Russia has a number of hypersonic weapons in development, with the Zircon the most promising. Russian officials have said they hope to be able to arm all new ships in the Russian navy with hypersonic weapons.

British officials have already voiced concern about the threat that Russian hypersonic weapons could pose to their carrier.

"Hypersonic missiles are virtually unstoppable," a senior British naval source told The Daily Mirror. "With no method of protecting themselves against missiles like the Zircon the carrier would have to stay out of range, hundreds of miles out at sea."

"Its planes would be useless and the whole basis of a carrier task force would be redundant," the source said.

The true capabilities of Russia's and China's new anti-carrier weapons are still unknown, but recent tests prove that US Navy carriers may not enjoy unquestioned dominance for much longer.