Two destroyers are returning to their homeport of Pearl Harbor today and the Bremerton, Wash.-based aircraft carrier USS John C. Stennis is visiting after exercise Valiant Shield 2007 wrapped up after eight days near Guam.

Three U.S aircraft carriers, 22,000 troops, more than 30 ships, and about 290 aircraft participated in a repeat of the big interoperability exercise that was first held last year.

The exercise, which ended last Monday, "tests the military's ability to rapidly bring together joint forces in response to any regional contingency," the Navy said.

The carriers Stennis, Kitty Hawk, and Nimitz and several Los Angeles-class attack submarines participated in the exercise, with the carrier strike groups defending against subs playing the role of enemy forces.

Anti-submarine warfare is the U.S. Pacific Fleet's top war-fighting priority with a proliferation of quiet foreign diesel-electric submarines in the Pacific.

Last October, a Chinese Song-class diesel-powered attack submarine surfaced within sight of the Kitty Hawk strike group in the East China Sea near Okinawa.

The Pearl Harbor destroyers Paul Hamilton and O'Kane are returning following the exercise and operations in the Persian Gulf region with the Eisenhower carrier strike group.

From the Persian Gulf region, Stennis' air wing flew more than 7,900 sorties in support of coalition forces on the ground in Iraq and Afghanistan, dropping 90,000 pounds of ordnance.

Exercises with three carriers off Guam later provided a host of challenges.

"Anytime you have a group of ships and an air wing working together with a carrier, it's a complex environment," said Lt. Justin Harts, the Paul Hamilton's operations officer. "With three carriers, you have three times the complexity. You're talking about trying to integrate three different common operating pictures. It's a lot to sort out."

More than 2,900 sorties were flown during the exercise, with KC-135 and KC-10 tankers offloading 2.29 million pounds of fuel to airborne aircraft.

U.S. Air Force B-52s, F-15Cs, F-16CJs, KC-135s and E-3 AWACS aircraft flew defensive counter air, electronic attack, suppression of enemy air defense, intelligence, surveillance and reconnaissance, aerial refueling, air interdiction, and anti-surface warfare missions to support the joint operations in the vicinity of Guam.

FA-18s, Hawker Hunter jets and Lear jets, along with Air Force F-16CJs and B-52s, flew more than 400 additional sorties as opposing forces during the exercise.

Thirteenth Air Force at Hickam Air Force Base was the overall lead agency for planning the joint U.S. exercise and also served as the joint force air component command under Joint Task Force-519.