In a changing world, and up until now, the Navy’s 3rd Fleet headquarters in San Diego has been underutilized in the Pacific. Its 7th Fleet in Yokosuka, Japan, has been extraordinarily busy.

For years, ships sent to Asia from the West Coast and Hawaii have fallen under operational control of the 7th Fleet once past the international date line. But Adm. Scott Swift, head of U.S. Pacific Fleet at Pearl Harbor, is changing that hard and fast rule.

Three Navy destroyers passing through Hawaii on their way to the Western Pacific will remain under the operational command of the 3rd Fleet for the duration of the seven-month deployment as part of a new initiative called “3rd Fleet Forward.”

The Momsen, Decatur and Spruance also are making history as a three-ship grouping called a “Surface Action Group” for most of the deployment — as opposed to deploying independently as a single ship or with an aircraft carrier strike group.

“I never understood from the whole time that I’ve been in the Pacific why we were so allegiant to the international date line as the separation between 3rd Fleet and 7th Fleet,” Swift told about 350 sailors from all three ships gathered on the Momsen on Tuesday in Pearl Harbor.

Both fleets are run by a three-star admiral and have depth in their staffs, the Navy said. But the 3rd Fleet until recently was seen as a force provider, “and that’s not the case,” Swift said after the “all hands call” with sailors. “3rd Fleet has all kinds of capability.”

“I saw a deficiency there that we had capacity and capability that we weren’t taking advantage of,” Swift said.

U.S. Pacific Fleet, which administratively controls the 3rd and 7th fleets, is responsible for a vast and heavily militarized region with seven of the world’s 10 largest militaries and five of the world’s declared nuclear nations, the Navy said.

Much of the U.S. focus is west of the date line, where China is increasingly at odds with the United States in the South China Sea and North Korea keeps advancing its nuclear weapons threats. The next natural disaster is always just around the corner. Engagement with allies and friends in the region is seen as key.

“We haven’t hit the capacity point with 7th Fleet,” but at some point “we could,” Swift said.

Navy news releases still use words like “demonstrate” and “concept” when describing “3rd Fleet Forward,” but Swift said he told Vice Adm. Nora Tyson when she became commander of the 3rd Fleet in July that this was what he wanted to do, and advised her to “start moving in that direction.”

It was Tyson who represented the Navy at Japan’s fleet review in October while the 7th Fleet was busy supporting an exercise in South Korea, Swift said. She also recently met with naval leaders in New Zealand and Australia, he said.

Swift said it’s not the case that more ships will be deployed to the Western Pacific under 3rd Fleet Forward, just that responsibilities will be shared.

Capt. Chuck Johnson, commander of Destroyer Squadron 31, is going along on the deployment because of its importance as a test.

“It’s going to get 3rd Fleet more operational, which really is going to be what drives more options for the Pacific Fleet commander,” Johnson said.

Each of the three West Coast destroyers has a crew of about 300, the Navy said. The Spruance will temporarily split off and head to the South Pacific for a visit to Tonga and help curb illegal fishing that runs into billions of dollars a year.

Swift said that with North Korea continuing nuclear weapons testing, “there may be a requirement to take advantage of that mobility and flexibility that we have in a three-ship (Surface Action Group)” and use the Decatur, with ballistic missile shoot-down capability, in the vicinity of Japan.

In 2017 the Marine Corps version of the F-35 Joint Strike Fighter is scheduled for its first operational deployment embarked on the amphibious assault ship USS Wasp forward in the Pacific, Swift said.

“I think it’s going to revolutionize where we are with expeditionary strike groups,” Swift added.

He said he plans to attach another three-ship surface action group with its added firepower to the Wasp.

“So that Wasp will be what I’m calling an up-gunned (expeditionary strike group),” Swift said.