Wildcat Infrastructure - a US company backed by a family of private investors - had made an offer between $US1.3 billion and $US1.4 billion to buy Austal's shipyard in the US state of Alabama, the Perth-based company said.
"The board and its advisors will consider the transaction made by Wildcat," chief executive Paddy Gregg said on Wednesday.
His message came after Austal paused trading in its shares, minutes before the market opened.
The halt was in response to a report published in The Australian speculating on a Wildcat's offer.
It's the second approach in a month for Austal's US security-critical arm, which is its biggest revenue generator.
The shipyard builds combat vessels and Virginia-class submarines for the US Navy and was responsible for more than three-quarters of Austal's 2025 revenue of $1.8 billion.
The South Korean multinational Hanwha put a non-binding offer between $US1.1 billion and $US1.2 billion on the table in August.
At the time, Austal's board told shareholders - including Hanwha, which holds 19 per cent - that the proposal required further evaluation.
It is unclear if a formal bidding war will ensue after Wildcat's non-binding proposal.
However, Austal's shares spiked by more than six per cent after it resumed trading on Wednesday.
The stock was up more than five per cent at $4.60 in early afternoon trading.
In August, Austal reported a 2025/26 net loss of $53.6 million, after booking a large item related to an "onerous contract" at the US business, which was denied relief by the US war department.
The Wildcat offer also comes amid a rift between Washington and Seoul.
US President Donald Trump took to social media and lashed out at South Korea for not providing military assistance with the ongoing Middle East conflict on August 17.
Joint military exercises between the two countries' naval forces were then cut short days later.
Austal may not reveal its verdict on Wildcat for another four weeks after the would-be predator asked for that time to conduct further due diligence. Hanwha is doing the same.
Austal is Australia's largest defence exporter and its first ASX-listed shipbuilder.
With shipyards in Australia, the US, Philippines and Vietnam, it has delivered both defence and commercial vessels to about 60 countries.
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