'EWA BEACH — An underwater explosion that was part of the ongoing Rim of the Pacific exercises rattled homes along 'Ewa Beach Road yesterday, but no one was injured.

The explosion at about 3:30 p.m. shook the walls of her home, said 'Ewa Beach Road resident Mary Jay. "It was a loud boom, like the depth charge (fireworks) on New Year's Eve and it rattled all the pictures on my walls," Jay said.

Capt. Steve Barrett of the HFD's Rescue 2 unit said divers searching murky waters for the cause of the explosion "pulled up a bunch of fiberglass containers and yellow floater" with Rimpac written on it.

"As part of the Rimpac exercise, EOD (explosive ordinance disposal) was conducting scheduled underwater demolition training in their designated training area at Pu'uloa Underwater Training Range," said Rimpac spokeswoman Cmdr. Dora Lockwood.

Lockwood said inert dummy mines were "located and detonated by small explosive charges." She added that a series of six charges were exploded.

However, the explosion may also have involved the detonation of a 16-inch round, officials said. It was unclear whether a 16-inch round was old ordnance discovered on the ocean floor or was transported to the training area.

"I don't have any details on the explosives that were used," Lockwood said, adding that information was not available last night. But she did say that "any charge that goes into the water will cause some type of plume. It's hard for me to say how big the plume was that people saw."

The training area just west of Pearl Harbor is on maritime charts and is 1,000 yards by 1,000 yards, an official said.

Residents reported hearing one loud explosion and seeing a plume of water about a mile offshore, not a series of small explosions.

Jeff Lono, 31, who lives in a beachfront house at 91-173 'Ewa Beach Road, had set up his fishing poles on the sand when he heard the explosion, moments after seeing a splash in the water.

"I saw the splash. It was 100 or 200 feet high and then the sound," Lono said. "I ran into the house to get my binoculars and saw two boats leaving the area."

Lono's friend, 23-year-old Joshua Shin, was body-boarding when he saw the splash. "There was this big splash and big black smoke," Shin said. "I had no idea what it was. I thought to myself kiddingly Kim (Jong-il of North Korea) almost made it this time."

HFD spokesman Capt. Terry Seelig said HFD and Coast Guard personnel searched for 90 minutes and did not find any evidence of anyone in trouble in the water or debris from damaged aircraft or watercraft.

Naval Special Clearance Team One out of San Diego has been conducting training off Hawai'i and was the unit training yesterday, Lockwood said. Hawai'i, Australian and British divers participated in explosive ordnance disposal training earlier this month.

Atlantic bottlenose dolphins were brought in from San Diego for earlier mine countermeasure exercises, but Navy officials said no marine mammals were being used in yesterday's training.

Lockwood said the Coast Guard was notified in advance of yesterday's exercise.

"I can't tell you the exact date that they were notified," she said, "... but I can tell you that yes, indeed, the Coast Guard was notified and they were supposed to release a notice to mariners. Whether that happened or not, I'm not able to tell you."

Coast Guard spokesman Petty Officer Michael De Nyse said one or more notices went out to mariners before yesterday, and right after the explosion, a call went out that everything went "according to protocol."

A helicopter and 41-foot vessel were dispatched after a false report came in that a helicopter had crashed, he said.

"We kind of thought that it was ... just the explosion that was going to happen, but of course, we get our assets out there," he said.

De Nyse said the Coast Guard transmitted radio warnings to mariners repeatedly throughout yesterday's eight-hour time window the Navy said it would be conducting the training.

Asked about notification to people on shore, De Nyse said "our protocol is notice to mariners."

Lockwood said the Navy had a boat on scene to ensure mariners didn't get close to the site.

Eight nations, more than 40 ships, six submarines, 160 aircraft and almost 19,000 service members are participating in the 20th Rimpac exercise.

Reach William Cole at wcole@honoluluadvertiser.com and Rod Ohira at rohira@honoluluadvertiser.com.