The new USS Illinois is expected to become the fifth and latest Virginia-class submarine to be based in Hawaii, adding to a capability that is very much in demand in a region shared with China, North Korea and Russia.

Adm. Harry Harris, head of U.S. Pacific Command, recently bemoaned the fact that the U.S. Navy is at 52 attack submarines and headed down to 42 in coming years with the retirement of older Los Angeles-class vessels. Even now, Harris said the Navy can meet only 50 percent of his submarine requirements.

“From a joint commander perspective, I need more submarines,” Harris told the House Armed Services Committee.

Pearl Harbor has 20 nuclear attack subs now — the largest U.S. concentration in the Pacific. Harris would like to see a fifth sub in Guam.

The 377-foot Illinois, now out of Groton, Conn., is in what’s known as a post-shakedown availability, or PSA, which involves taking the submarine back to the initial delivery yard to correct any remaining deficiencies, Cmdr. Tommy Crosby, a spokesman for the Atlantic Fleet Submarine Force, said in an email.

“Upon completion of PSA, the submarine will report to its final homeport as designated by the Chief of Naval Operations where it will then begin its work-up and preparation for its maiden deployment,” Crosby said.

The Navy still isn’t confirming the Illinois’ move to the Pacific. “Nothing has been officially announced and we won’t speculate until the announcement is made,” Lt. Cmdr. Gustavo Perez, a Pacific Fleet Submarine Force spokesman, said in an email.

The arrival of the Illinois, which was christened by former first lady Michelle Obama, would bring $2.7 billion worth of additional high-tech underwater stealth to the Pacific. Former Navy Secretary Ray Mabus called the USS Illinois “one of the most technologically advanced platforms in the world” when the ship was commissioned in October.

“In this time, where you have all the uncertainty about North Korea, there really is no better, in my opinion, best defense that we could have (than) the subs,” said U.S. Rep. Colleen Hanabusa, D-Hawaii, a member of the House Armed Services Committee.

The Virginia-class subs can dive to more than 800 feet and operate at more than 29 mph submerged. The subs have been improved to operate in littoral, or nearshore, environments and can accommodate special operators in a reconfigurable torpedo room. Traditional periscopes have been replaced by two photonic masts with infrared and digital cameras atop telescoping arms.

The Illinois would be the first “Block III” Virginia-class submarine in Hawaii with two “six-shooter” 87-inch Virginia payload tubes, each capable of launching six Tomahawk cruise missiles, mounted in the bow in removable canisters. Other Virginia subs in Hawaii have 12 individual vertical- launch-system tubes.

The traditional air-based sonar sphere in the bow has been replaced with a water-backed “large aperture bow” array, which the Navy said reduces costs and enhances passive detection capabilities.

Harris told members of Congress that the submarine force deals with “the Russian submarine threat, the Chinese submarine threat, and they’re also involved in surveillance missions and other kinds of missions.”

About 230 of the world’s 400 foreign submarines are in the Indo-Asia-Pacific, with about 160 of those belonging to China, Russia and North Korea, Harris said. Potential adversary submarine activity has tripled since 2008, he said.

Harris said he supports the Navy’s 2016 force structure assessment, which calls for a 355-ship Navy, including 66 attack subs. The Pacific commander said the United States “must preserve” its asymmetric advantages in undersea and anti-submarine warfare.

“I believe that there is no submarine on the planet that can touch an American submarine — (a) Virginia-class submarine,” Harris told Congress. “That said, that gap between the next best, third best, is closing.”