Under the AUKUS deal signed to great fanfare in 2021, Washington, London and Canberra are cooperating on the joint development of cyber warfare tools, artificial intelligence and hypersonic missiles.

The agreement commits the United States to building cutting-edge submarines for Australia, an investment with an estimated cost of up to $235 billion over 30 years.

Australia plans to acquire at least three Virginia Class submarines from the United States within the next 15 years, eventually manufacturing its own nuclear-powered subs.

The US navy has 24 Virginia-class vessels, which can carry cruise missiles, but American shipyards are struggling to meet production targets set at two new boats each year.

Critics question why the United States would sell nuclear-powered submarines to Australia without stocking its own military first.

Questioned by members of the US House of Representatives, Hegseth said his team was talking "every day" to US shipbuilders Electric Boat and Huntington Ingalls to ensure that "their needs not only are being met, but their shortfalls are being addressed."

The former Fox News host, one of President Donald Trump's most divisive cabinet appointments, acknowledged a "gap" between current supply and future demand, but added that submarine building is "crucial" to US security.

He blamed Trump's Democratic predecessor Joe Biden for having "neglected" the industrial base for submarine construction.

While the stealthy Virginia class is an attack and intelligence gathering submarine designed for a wide range of missions, the Columbia class is a ballistic missile carrier built for nuclear deterrence that will be the largest submarine ever built by the United States.

Democrat Rosa DeLauro -- whose home state of Connecticut builds Navy submarines -- berated Hegseth over the Pentagon's decision to move $3.1 billion earmarked in 2026 for Columbia-class construction to 2027 and 2028.

"Is that going to raise alarm bells across the defense industrial base by signaling a lack of commitment to the program?" she asked.

Hegseth committed to the "on-time" delivery of the vessels.