NEW YORK -- U.S. Deputy Secretary of Defense Kathleen Hicks has kicked off a multistate trip in New England -- a hub of military installations vital to taking on a rising China, including sites for building and maintaining submarines and destroyers.

Hicks visited two shipyards in Maine on Wednesday, one federally owned and the other private.

The Portsmouth Naval Shipyard in Kittery, Maine, is one of the U.S. Navy's four remaining public shipyards. It handles maintenance and modernization work for Los Angeles- and Virginia-class nuclear-powered fast attack submarines.

The U.S. had nine active public naval shipyards until the mid-1990s but shut many down as the Cold War ended and the defense budget shrank. The four survivors are more than a century old, and lawmakers have raised concerns that the outdated dry docks cannot handle the newer vessels that will be crucial in the great-power competition.

In Kittery, Hicks received a briefing on one of the modernization efforts known as the "super flood basin." This project will allow the seawater level to be raised and lowered so that submarines can enter and leave Dry Dock No. 1 independent of the Piscataqua River tides.

"Dry Dock No. 1 is the shallowest of the three dry docks at the shipyard and required a buoyancy assist system comprised of large floodable air-filled tanks in order to dock and undock submarines," Portsmouth Naval Shipyard public affairs officer Danna Eddy told Nikkei Asia. "The basin, similar to a navigational lock, is being constructed at the entrance of the dry dock and enables submarines to be docked 365 days per year without buoyancy assistance."

Workers at Portsmouth Naval Shipyard successfully undock the Los Angeles-class submarine USS San Juan from a routine engineered overhaul. (Photo courtesy of the U.S. Navy)

Currently, submarines can make entry on only a handful of days per month, owing to tidal conditions, and the bottleneck in repairs has held down the number of available subs in the fleet.

The upgrade will be especially important as the Navy introduces the longer "Block V" type of Virginia-class submarines, which will be fitted with an extra section in the middle to serve as a vertical launcher for Tomahawk missiles.

China is the world's top ship-producing nation by tonnage and is "increasing its shipbuilding capacity and capability for all naval classes," according to the Pentagon's annual report to Congress on Chinese military and security developments.

A bipartisan group of U.S. lawmakers has proposed a $25 billion infusion into outdated public and private naval shipyards, and upgrades are underway at all four of the public sites. The other public shipyards are the Norfolk Naval Shipyard in Virginia, the Puget Sound Naval Shipyard in Washington, and the Pearl Harbor Naval Shipyard in Hawaii.

U.S. Deputy Defense Secretary Kathleen Hicks visits the Bath Iron Works shipyard in Bath, Maine, on July 7. (Photo courtesy of the Department of Defense)

Also on Wednesday, Hicks went to the privately owned Bath Iron Works in Brunswick, Maine, where General Dynamics builds Arleigh Burke-class and Zumwalt-class destroyers. She visited the future USS Daniel Inouye -- an Arleigh Burke-class destroyer named after the late Japanese American senator -- and met troops assigned to the ship.

The Arleigh Burke class is the current mainstay destroyer of the U.S. Navy but has been the target of restructuring in Pentagon's latest budget request as the Navy prioritizes assets more fitted to a potential conflict with China, such as submarines.

How to plan for the future of the Arleigh Burke class will be a major point of discussion as the Pentagon and Congress work on the defense budget.

For Thursday, Hicks' itinerary included discussions at Harvard University and the Massachusetts Institute of Technology on "the importance of academic partnerships to the Department's modernization priorities, including rapid experimentation and the adoption of artificial intelligence," according to a Pentagon announcement.

The trip takes Hicks through Maine, New Hampshire, Rhode Island, Connecticut and Massachusetts. It includes a visit to General Dynamics Electric Boat -- the builder of the new Columbia-class ballistic missile submarines, which will be constructed in Rhode Island to replace the current Ohio class starting around 2031 and form one leg of the U.S. nuclear triad.