ABOARD THE USS PELELIU — The diesel submarine lurks somewhere south of O'ahu, and the Peleliu, with thousands of U.S. sailors and Marines aboard, is the "high value" target it is hunting.

The cat-and-mouse game pits the quiet of a relatively inexpensive foreign sub against the high-tech listening capabilities of Expeditionary Strike Group 3 and its five ships, as well as two Hawai'i-based destroyers and a Canadian frigate.

The USS Port Royal, a Pearl Harbor-based guided missile cruiser that's part of the strike group, has a powerful sonar that protrudes underwater from the keel of the ship, and a towed array that can trail 2,600 feet behind and listen at varying depths.

Sonar technician Erin Guzman, 24, from Albuquerque, N.M., would push the button to launch a torpedo from the Port Royal in the case of an actual hostile encounter.

The exercise has its own adrenalin-filled moments.

"We had a possible contact (and) I was asking what bearing it was at," she said yesterday. "It can get real intense. If we have contact out there, we have a lot of things going on at once with all our sensors."

With all those figurative ears listening, eyes scanning for periscopes, and P-3 Orion sub hunting aircraft from Kane'ohe Bay flying overhead, it's still a good match-up.

"It's hard. They (diesel subs) are very quiet. That's why we do so many exercises," said Capt. Dave Matawitz, the Port Royal's commanding officer.

Such exercises in Hawai'i's waters are on the rise.

With the proliferation of diesel submarines in the Pacific, Adm. Gary Roughead, who commands U.S. Pacific Fleet from Pearl Harbor, has made anti-submarine warfare the fleet's top maritime war-fighting priority.

"The challenges that I see at the high end are anti-submarine warfare. There are about 140 diesel submarines that operate in the Pacific," Roughead said recently at an Asia Society gathering in Washington. "We, as a Navy, are good at anti-submarine warfare. We can always get better, and that's what we're doing because we have to be able to dominate that growing submarine capability."

Roughead has mandated that all aircraft carriers and expeditionary strike groups deploying from the West Coast conduct several days of anti-submarine warfare, or ASW, training, in Hawai'i waters.

The USS Ronald Reagan aircraft carrier strike group was the first in mid-January. Expeditionary Strike Group 3, which today wraps up a three-day exercise, is the second.

The new requirement means more port calls for the multi-ship strike groups in Pearl Harbor, and the amphibious assault ship Peleliu, the amphibious transport dock ship Ogden, and the dock landing ship Germantown — all out of San Diego — will be in Hawai'i for a brief stay before deploying to the Persian Gulf region.

There has always been some degree of anti-submarine warfare practice for the deploying strike groups.

What's different now is "the intensity, location (near Hawai'i), and we're acting as one battle group" for the training, Matawitz said.

Capt. Peter Morford, the commodore of Amphibious Squadron 3, which includes the flagship Peleliu, said submarine hunting is a complex and changing art.

"It's kind of the ultimate in perishable knowledge," he said yesterday, "and this is just a mission area where we need to train, train and train some more."

Gone is the "Cold War, Soviet submarine threat, 'Hunt for Red October,' " Morford said.

The Heritage Foundation previously reported that China's roughly 70 submarines included one ballistic missile submarine and five attack subs, that North Korea had the fourth largest submarine fleet with 26 diesel subs, and Iran had six subs.

Experts say that China lags far behind the U.S. militarily, but one day may have more subs than the U.S.

A recently released 20-year roadmap for the U.S. military called the Quadrennial Defense Review states that the Navy will have a "greater presence" in the Pacific because of the shift in trade and transport to that region and China's growing power.

"Accordingly, the Navy plans to adjust its force posture and basing to provide at least six operationally available and sustainable carriers and 60 percent of its submarines in the Pacific," the plan says.

About 35 attack and ballistic missile submarines are based in the Pacific and an equal number in the Atlantic, the Navy said. Sixteen attack submarines are based at Pearl Harbor.

In the meantime, the Navy practices off San Diego against diesel submarines like the Gotland, an advanced Swedish sub.

The three-day exercise concluding today had the contingent of eight ships spread out, in some cases miles apart, some 30 to 50 miles south of O'ahu.

An unidentified Los Angeles-class nuclear attack submarine from Pearl Harbor played the aggressor, periodically surfacing to replicate a diesel sub.

"The submarine is out here to go against us, and we against them," Morford said. "They are trying to find us and attack us, and we're trying to prevent that from happening."

Morford declined to say how the sub hunt was going because it gets into an operational area he didn't feel at liberty to discuss.

Capt. Matt Brown, a U.S. Pacific Fleet spokesman, said Hawai'i's waters represent a "unique confluence of factors" for anti-submarine warfare training.

Attack subs and sub-hunting aircraft like the P-3 Orion are based here and can take part in exercises. The archipelagic island chain produces sound profiles very different from the West Coast.

"This replicates in some ways situations in Southeast Asia, the West Pacific and Indian Ocean," Brown said.

Matawitz, the commander of the Port Royal, sometimes takes part in anti-submarine warfare exercises with other strike groups.

"I've done more ASW in the last year than the previous 22 years in the Navy," he said. "We have done a lot of ASW."

The guided-missile frigate Reuben James also is part of Expeditionary Strike Group 3 and is deploying to the Persian Gulf.

P-3 Orion aircraft with Patrol Squadrons 4 and 9 from Kane'ohe Bay were taking part in the three-day exercise. The aircraft drop 4-foot sonobuoys that blanket an area and can listen passively or with sonar for submarines.

Lt. j.g. Warren Keierleber, with Patrol Squadron 4, was on board the Peleliu as a liaison for the exercise. These days, a lot more ships and aircraft are involved in anti-submarine warfare, he said.

"It's really good to work with the ships because on today's battlefield, you are working a lot closer with friendly units," he said.

Reach William Cole at wcole@honoluluadvertiser.com.