The USS Bowfin Submarine Museum and Park, the most visited submarine museum in the world, is adding a modern update to its storied namesake’s World War II past.

Officials broke ground Monday on a $20 million revitalization and expansion at the sub museum’s Pearl Harbor location next to the USS Arizona Memorial visitor center.

The updated museum will include three exhibit galleries that span the history and future of submarine warfare: the submarine force of World War II, the Cold War and today’s force and into the future.

When the changes are completed in April 2020, it will get a new name: the Pacific Fleet Submarine Museum.

Executive Director Chuck Merkel said the groundbreaking “is a significant milestone as we take a major step toward achieving our vision of revitalizing our campus to better honor the past and inspire the future.”

The lawn ceremony was set against a busy Pearl Harbor backdrop of hundreds of visitors milling around the Bowfin and Arizona Memorial visitor center grounds.

The latter has remained open since the partial government shutdown on Dec. 22 due to ongoing donations of hundreds of thousands of dollars from the Bowfin and other nonprofits that operate in Pearl Harbor, the state of Hawaii and the tourism industry.

Patience is wearing thin with the lengthening cutoff in funding to attractions like the Arizona Memorial.

“It needs to end. It’s a mess,” Marc Zimmerman, 39, said of the shutdown. He and his wife, Cheryl, who are from San Francisco, were at the Bowfin and earlier visited the Arizona Memorial.

“I’m in the restaurant business, and I know a lot of brewers that are having trouble getting anything from (Alcohol Beverage Control) or anything from any kind of government agencies,” Marc Zimmerman said.

The couple didn’t even think about the furloughs until they got to Oahu.

“Our concierge said get over here fast (to the Arizona Memorial) because they didn’t know how long it was (going to be open),” he said.

Pacific Historic Parks, a nonprofit that supports the Arizona Memorial, announced Friday it had received pledges of more than $200,000 from Hawaii’s tourism industry to keep the memorial open through this month.

During the Bowfin’s renovation, portions of its campus will be closed to the public during construction, but its centerpiece submarine will remain open throughout the project.

In the aftermath of Dec. 7, 1941, much of the U.S. Pacific Fleet surface force at Pearl Harbor was in shambles. Twenty-one ships, including eight battleships, were sunk or damaged.

But the Navy still had another weapon to which it could turn: Pacific submarines immediately began war patrols.

The USS Bowfin was launched a year after the attack, on Dec. 7, 1942 — receiving the nickname the “Pearl Harbor Avenger.” Between 1943 and 1945 the Bowfin went on nine war patrols, claiming a total of 44 vessels sunk.

Eighty men lived and worked for 60 days at a time inside the cramped steel tube, which is 16 feet in diameter.

The museum is enlarging to 12,000 from 9,000 feet, and a new entry will blend better with a 2010 renovation of the Arizona Memorial campus, Merkel said.

“It’s going to really inspire more people to come over and take a look,” Merkel said. The museum, meanwhile, “is going to be completely redone,” he said.

The groundbreaking took place next to a big “Kaiten” Japanese suicide torpedo with a cramped space for a pilot. The weapon was mounted with a 3,000-pound warhead.

In the museum is a C-3 Poseidon nuclear ballistic missile mock-up that’s 74 inches in diameter and 32 feet long.

Merkel said he’s working with the Navy to get a full-size modern torpedo replica and pieces of Los Angeles-­class subs that are being decommissioned.

The year 2017 saw record attendance for the Bowfin with 420,000 paid admissions, he said. That was after 390,000 came through in 2016.

The museum had its challenges in 2018, including being closed for five or six days during two hurricanes.

A halt to walk-on access to the Arizona Memorial in March due to a failing dock — which still hasn’t been fixed — has taken a toll on attendance for all the nonprofit museums in the harbor, including the Battleship Missouri Memorial and Pearl Harbor Aviation Museum.

For 2018 the Bowfin had just over 400,000 visitors, “so slightly down but still our second-best year,” Merkel said.