Hong Kong (CNN) The US Navy on Monday awarded its most expensive shipbuilding contract ever, more than $22.2 billion worth of the world's most advanced submarines.

The massive contract for nine nuclear-powered, Virginia class attack submarines comes just months after the head of the US Navy in the Pacific warned of a massive Chinese naval buildup and his trouble in getting enough submarines to counter it.

The deal "marks the US Navy's latest response to China's growing military power and aggressive actions in the Western Pacific," said Carl Schuster, a former director of operations at the US Pacific Command's Joint Intelligence Center.

"The PLAN (Chinese Navy) is getting better and larger so the US Navy has to respond," he said. "It doesn't make China an enemy, but China's actions do bear watching."

Virginia class submarines are the US Navy's key multi-mission undersea platform. They are capable of fighting other submarines, surface ships and land targets, as well as conducting special operations including intelligence gathering and reconnaissance.

Eighteen of the subs are already in the Navy's fleet with another 10 in various stages of construction.

But the nine new subs will represent a substantial upgrade over their predecessors in the class. The Navy also has an option for a 10th sub in the contract, which would bring its value to $24 billion.

'A generational leap' in capability

Rear Adm. David Goggins, the Navy's program executive officer for submarines, called them "a generational leap in submarine capability for the Navy" in a statement on the Navy's website Monday.

They'll be bigger, displacing 10,200 tons compared to 7,800 on the current subs; they'll be longer, 460 feet compared to 377 feet; and they'll have substantial more firepower, with the ability to launch strikes with 40 Tomahawk cruise missiles, compared to just 12 on the current ships.

The subs, which can generate their own water and oxygen, can stay submerged for months at a time.

"Our submarine force is fundamental to the power and reach of our integrated naval force," said acting Secretary of the Navy Thomas B. Modly. "Today's announcement affirms our commitment to the future strength of our nation, undersea and around the world."

US Sen. Jack Reed, D-Rhode Island, the ranking member of the Senate Armed Services Committee, hailed the new contract.

"These next generation submarines provide our forces with a distinct national security advantage. They are an unmatched tool for deterrence," Reed said in a statement.

The submarines will be built by prime contractor General Dynamics Electric Boat, based in Groton, Connecticut, with subcontractor Huntington Ingallls Industries. Sen. Reed said the contract would ensure a stable workload for the 4,000 workers at an Electric Boat shipyard in Rhode Island for years to come.

While the nine new subs will be additions to the fleet -- the first of the Virginia class was delivered in 2004 -- they will be needed to replace some of the Navy's aging Los Angeles-class attack subs, which first entered the fleet in the 1970s.

The new submarines are scheduled for delivery between 2025 and 2029, the Navy said.

The naval balance in the Pacific

Experts say the US is facing unprecedented pressure in the Pacific, largely from a Chinese navy that has been making huge leaps in the numbers and quality of its submarine fleet.

The May 2019 China Military Power Report from the US Defense Department said the People's Liberation Army Navy will field 65 to 70 submarines by 2020.

JUST WATCHED U.S. aircraft carrier stalked by submarine Replay More Videos ... MUST WATCH U.S. aircraft carrier stalked by submarine 02:08

Beijing's force is expected to grow from there, with China in the next five years expected to begin churning out advanced nuclear-powered attack subs similar to the US Virginia class.

An August report from analysts in Australia questioned the US's ability to keep up with China's advances and warned that Washington is facing a crisis of "strategic insolvency."

"Put simply, as the environment above the surface becomes more deadly because of Chinese deployments of cruise missiles, hypersonic technologies and anti-air defenses, America's enduring advantage in undersea warfare will become increasingly important in the regional balance of power," the report said.

JUST WATCHED The nuclear-powered sub challenging Russia in the Arctic Replay More Videos ... MUST WATCH The nuclear-powered sub challenging Russia in the Arctic 04:58

Adm. Philip Davidson, the head of US Indo-Pacific Command in Hawaii, told Congress earlier this year the submarine activity by three US adversaries in the Pacific -- China, Russia and North Korea -- has increased threefold since 2008.

Davidson said he needed to match that increase to keep US naval superiority in the region, but he needed the boats to do it.

However, he told Congress in March that he was only getting half of the submarines needed in the Pacific on a daily basis.

And things were looking stark for the US fleet in the future, Davidson said.

"We're going to lose our quantitative edge in about the 2025 timeframe. I think that's going to be a challenge for our equities in the region," he said.