The Navy says it wants to spend $5 billion over 20 years to improve Pearl Harbor shipyard’s aged infrastructure and to accommodate an expected increase in Virginia-class attack submarine work.

Among the changes, the Navy plans to extend Dry Dock 3 inland and improve its ocean access, as well as modify Dry Dock 4 — used for surface-ship work — to better support submarine maintenance.

The improvements are planned, in part, to accommodate new Virginia-class submarines that will be 84 feet longer than the current 377-foot subs due to the inclusion of a “Virginia Payload Module” capable of firing an additional 28 Tomahawk or anti-ship missiles.

“Much of Pearl Harbor Naval Shipyard &Intermediate Maintenance Facility was constructed before and during World War II. In the intervening 75-plus years there has been little change to the four dry docks and major facilities,” said Cmdr. Scott Shea, the shipyard’s deputy commander, in an email. “Given innovations in ship and submarine design, upgrading our facilities is critical to keep pace with evolving technologies and improve the effectiveness and efficiency of our maintenance efforts.”

That evolving submarine work has the surface-ship repair industry in Hawaii worried it will be forced out of Dry Dock 4 and eventually sail away to San Diego, along with the economic impacts it brings.

The Pearl Harbor shipyard is the largest industrial employer in Hawaii, with a workforce of approximately 5,200 civilians and 600 military members who primarily support submarine work. An additional 1,000 or so civilian employees repair Navy surface ships at Dry Dock 4 through an ongoing contract with BAE Systems’ Hawaii Shipyards.

“By 2022 there will be so many Virginia-class (submarines) home-ported at Pearl Harbor that the Navy will have to use Dry Dock 4 to accomplish their dry-docking availabilities,” the Ship Repair Association of Hawaii said in a state grant request early this year.

The association asked for $234,600 to study the Navy’s dry-docking needs at Pearl Harbor, and in particular the economic consequences of removing surface-ship work from Dry Dock 4.

The 497-foot-long Dry Dock 3, completed in 1942, will “require significant modifications to accommodate the (new) Virginia-class submarines,” the association said in its grant request. “Estimates are as high as $400 million and approximately eight to 10 years to program the money and obtain the extensive regulatory permits anticipated for this environmentally sensitive project.”

Six of the shorter-version Virginia subs are based at Pearl Harbor now, along with older 360-foot Los Angeles-class vessels.

The Navy’s most immediate solution for the 10 surface ships home-ported at Pearl Harbor would be to move them to the West Coast for dry-docking and major maintenance work, the association said, resulting in layoffs and a loss of “core knowledge of these complex ships” in Hawaii.

The association suggested the Navy construct a floating dry dock to accommodate all sizes of surface ships and submarines in Pearl Harbor.

Naval Sea Systems Command, which oversees the Navy’s four public shipyards, provided some information about the shipyard improvement plan but said it had no comment on the Ship Repair Association’s proposal.

The Navy will start procuring the longer, more capable $3.2 billion Virginia submarines starting this fiscal year, and plans for all Virginia subs built after that to have the 84-foot payload module, according to the Congressional Research Service.

A 2017 Government Accountability Office report noted that a dry-docking shortfall for the newer subs is exacerbated at Pearl Harbor because Dry Dock 2 can be divided in two length-wise to support two current Virginia subs, but it can accommodate only one of the longer versions, further reducing maintenance space.

The Navy said planned improvements to Dry Dock 3 include enlarging it on the inland side and building a flood basin at the seaside entrance to eliminate the need for “buoyancy-assisted modules” to assist subs getting into the dry dock.

Officials also said there is no plan to make Dry Dock 4 a submarine repair dock only.

A September Navy report on the overall $21 billion plan to overhaul all four shipyards noted the requirement is “well beyond the Navy’s historical facilities investment funding” and would require special budget attention.