Lincoln limits sonar in war games

ABOARD THE USS ABRAHAM LINCOLN — A sonar technician listening through his headset caught the trail of an enemy submarine just before a line of warships cruised through waters between Catalina and San Clemente Island off the California coast.

The whooshing sound of bubbles created by the submarine’s propeller had been picked up by passive acoustic monitoring. The detection — part of a sophisticated naval training exercise over the weekend— popped up on green and red-lighted screens in command centers aboard the aircraft carrier and its support ships.

If not for a recent federal court order, the accompanying destroyers would have begun to track the submarine by activating a powerful sonar that issues a loud ping and then waits for the echo to reveal the target’s location.

But at times last weekend, the sonar had to be turned off. A judge concerned about the potential harm to whales and dolphins forbade its use in the narrow strait between the islands, waters known for their rich abundance of marine mammals. The submarine soon got away in the murky depths.

And so began the war games that continue this week, a final exam after months of training to determine if the carrier strike group led by the Everett-based Abraham Lincoln is prepared to met threats of all kinds — including submarine attack — before it heads for the Persian Gulf in March.

“This is a game of cat and mouse,” said Navy Secretary Donald Winte. “Any time we have to shut down our sonar creates huge problems for us. We want to do everything we can to protect the whales, but not risk compromising our training.”

Testing for weaknesses

The 6,500 sailors on six ships aren’t tuned in to the legal and constitutional challenges happening on shore. Each is focused on individual tasks in an elaborate choreography masterminded by Vice Admiral Samuel Locklear III, commander of the U.S. 3rd Fleet.

Locklear said he is working from a secret playbook that will test sailors’ mettle, distract them, spread the ships thin and probe for weaknesses. “They don’t know what’s coming,” he said.

Throughout the weekend, fighter jets catapulted off the aircraft carrier and then returned at night to make tail-hook landings on deck in stormy seas. Meanwhile, destroyers were maneuvering to sweep the horizon for hostile boats and scan beneath the waves for submarines.

As soon as the strike group moved south of the islands, the destroyers were allowed under the terms of the court order to turn on the midfrequency active sonar. The powerful sonar is used to hunt for the type of quiet diesel-electric submarines now operated by Iran and three dozen other countries.

By midafternoon Saturday, the strike group located the enemy submarine with the ship-based sonar. Helicopters were dispatched with a special dipping sonar that was lowered by cable into the water. The ships tracked the enemy sub for awhile, but it managed once again to elude them.

At 2 a.m. Sunday, the target submarine — a U.S. sub playing the role of the enemy — surfaced near the carrier and radioed to announce its location.

“It’s very embarrassing that the submarine got in on us,” said one Navy captain. “But it shows how a submarine can hide among pinnacles and sea mounts and we’ll have to learn from it.”

Tracking submarines isn’t easy even with the powerful sonar. One problem is that the ocean creates is layers of water with different temperatures. Sonar can bounce off lower, colder layers, and clever submarine crews learn to mask their whereabouts by hovering beneath them. Another challenge is submarines can find hiding places in the nooks and crannies around islands and undersea mountains.

Strategy to protect whales

But these places also attract whales, dolphins and other marine mammals. So conservation groups and the California Coastal Commission have been pushing the Navy to be extra careful when using sonar in these areas to avoid harming marine mammals.

Although the Navy maintains that there’s no evidence that these training mission have killed marine mammals in Southern California, other naval exercises using midfrequency sonar have been linked to whale and dolphin deaths in the Bahamas, the Canary Islands and elsewhere.

On Sunday, the crew aboard the destroyer Momsen showed Winter its multilayered strategy to protect whales. The efforts included reducing the power of midfrequency sonar by 75 percent any time a marine mammal was spotted within 1,000 yards. Sailors trained as lookouts scanned the horizon through powerful binoculars for whales and dolphins as sonar technicians listened for the great mammals.

Winter said he was impressed with how the crew responded to an imagined whale sighting. Technicians quickly turned down the sonar power and then shut it off when the whale ventured within 200 yards.