Three aircraft carriers filled the skies with fighters as one of the largest U.S. military exercises in decades got underway Tuesday off this tiny island in the western Pacific.

For the first time ever, a Chinese delegation was sent to observe the U.S. war games. But as the show of American military power began, North Korea — one of the region's most unpredictable countries — was rattling some swords of its own.

The maneuvers, dubbed "Valiant Shield," bring three carriers together in the Pacific for the first time since the Vietnam War. Some 30 ships, 280 aircraft and 22,000 troops will be participating in the five-day war games, which end Friday.

The exercises are intended to boost the ability of the Navy, Air Force and Marines to work together and respond quickly to potential contingencies in this part of the world, U.S. military officials said. Even U.S. Coast Guard vessels were joining in the maneuvers.

"The exercises are taking place on land, sea, air, space and cyberspace," said Senior Master Sgt. Charles Ramey. "They cover the whole spectrum."

The maneuvers mark the first major operation in this remote U.S. territory about halfway between Hawaii and Japan since the announcement last month that some 8,000 Marines would be moved here from Okinawa in part of the biggest realignment of the U.S. forces in Asia in decades.

Though planned months ago, they come amid heightened concern in Asia over North Korea.

Officials in the United States, South Korea and Japan say they believe North Korea is preparing to test launch a Taepodong 2 long-range ballistic missile. The missile is believed be able to reach parts of the western United States.

Pyongyang shocked Tokyo by launching a Taepodong that flew over Japan's main island in 1998. North Korea claimed the launch successfully placed a satellite in orbit, but that claim has been widely disputed.

North Korean leader Kim Jong-il agreed on a moratorium on long-range missile launches during a summit with Japan in 1999. Pyongyang has honored that agreement since, but Tokyo has threatened to impose sanctions if it goes through with the launch this time.

Military officials here had no comment on the activity in North Korea, or on what specific tactics or scenarios are being used in the exercises.

They stress, however, that the exercises have been opened to outside observation and are not intended to provoke North Korea.

"These exercises are not aimed at any one nation," said Cmdr. Mike Brown.

The exercises are instead intended to provide training in "detecting, locating, tracking and engaging" a wide range of threats in the air, land and sea.

Representatives from China, Japan, Australia, South Korea, Russia and Singapore were invited to attend.

China's presence has been singled out as particularly significant.

Though military relations between Beijing and Washington cooled when an American spy plane was captured in 2001, senior U.S. military officials are cautiously trying to mend the rift. At the same time, the Pentagon has expressed strong concern over the secrecy that shrouds China's rapidly modernizing military.

Adm. William J. Fallon, the top U.S. commander in the Pacific, said before the exercises began that implicit in the invitation was the expectation that China would reciprocate.

China's 10-member delegation includes one top-ranking officer each from the People's Liberation Army, air force and navy, the official Xinhua News Agency said Tuesday.

"The invitation to observe the U.S. military exercises is a very important component of exchanges between the militaries of China and the United States," Xinhua quoted an unidentified Defense Ministry official as saying.

Along with the USS Kitty Hawk, Ronald Reagan and Abraham Lincoln carrier strike groups, U.S. force fighters and B-2 bombers operating out of Guam's Andersen Air Force Base will join the maneuvers.

Brown said the exercises were to be held again next year, and then become a biennial event.