The USS Belleau Wood, an aircraft carrier-like ship and the largest to be sunk in Rim of the Pacific naval exercises, was putting up one last fight yesterday 50 miles northwest of O'ahu.

So was the 511-foot ammunition ship USS Mauna Kea, named after the Big Island landmark and the tallest mountain in the Hawaiian chain.

Both decommissioned ships were pummeled with missiles and bombs from other ships and aircraft yesterday as the monthlong multi-country naval exercise continued. And both were still afloat in the late afternoon.

"They are going to keep shooting at them until we run out of whatever ordnance we brought," said Capt. Jill Votaw, a Rimpac spokeswoman.

The endurance of the vessels is testimony to their design and a rare opportunity to test weapons like missiles at sea. In the case of Belleau Wood, an amphibious assault ship, the resilience also is a reflection of its sheer size: 833 feet and displacement of 39,300 tons.

Commodore Bruce Donaldson, commander of the Canadian Fleet Pacific and the Rimpac deputy commander, said that while computer modeling is an important and cost-effective tool, personnel only really can be evaluated under live-fire conditions.

"Live missile firings also give the ship's technicians and combat teams confidence in their equipment, a critical factor and a morale booster for those who may be called upon to sail into harm's way," Donaldson said in a release.

Eight nations, more than 40 ships including the aircraft carrier USS Abraham Lincoln, six submarines, 160 aircraft and almost 19,000 service members are participating in the 20th Rimpac exercise, conducted since 1971 off Hawai'i.

Canadian ships Algonquin and Vancouver fired SM-2 anti-air and long-range Harpoon missiles in the "sink exercise" involving the Belleau Wood and Mauna Kea.

An 80-foot sludge removal barge was sunk on Sunday, the Navy said, and the combat stores ship USNS Mars is expected to be sent to the bottom — in this case more than a mile deep — next week.

At least eight decommissioned Navy ships — most of them frigates and destroyers — have been sunk northwest of Kaua'i since 2000 during Rimpac exercises.

The USS Mobile Bay, South Korean and Canadian P-3C Orion aircraft, and U.S. Navy aircraft were expected to shoot at the Belleau Wood and Mauna Kea.

Submarine torpedoes were being reserved "unless nothing else will make it go down," Votaw said. "One well-placed torpedo will take it out."

Votaw said a ship like the Belleau Wood isn't used for an artificial reef because of the depth in the target area and because "it's not going down in one piece. It's going down, hopefully, in a lot of little pieces."

To meet environmental standards, all fuel, oil and other fluids are removed and the lines are flushed before sinking. The Navy said its policy is not to release photos of the sink exercises.

Scott Watson, 41, of Lakeland, Fla., who served on the Belleau Wood from 1986 to 1990, attended the decommissioning in October in San Diego.

"It's such a big part of your life. It's almost like you grow up on a ship," he said. "You make a lot of good friends."

In 1992, landing craft and helicopters from the ship delivered trucks, bulldozers, portable toilets, water purification equipment and food to victims of Hurricane Iniki on Kaua'i.

In 2004, it deployed to the Persian Gulf with helicopters and AV-8B Harrier jump jets. More than 60 combat sorties were flown off its flight deck. Watson went on two Western Pacific deployments.

Watson is glad the ship is being sunk and not scrapped.

"It's doing its last duty," he said. "I'd rather see her on the bottom than turned into a bunch of Buicks. It's a more fitting resting place."

Reach William Cole at wcole@honoluluadvertiser.com.