Australia is set to start a major overhaul of its aging Collins-class submarines later this month. The goal is to prevent a gap in undersea defense before new nuclear-powered submarines arrive through the AUKUS security pact.

Defense Minister Richard Marles confirmed Tuesday that the first submarine, HMAS Farncomb, will begin a major refurbishment program at the end of May. The submarine displaces 3,100 long tons when surfaced, and 3,353 long tons when submerged.

This project is part of an $11 billion plan to keep the diesel-electric fleet running into the 2040s, while Australia waits for U.S.-built Virginia-class nuclear submarines expected to arrive in the next decade.

The life-extension plan will extend the service life of the six Collins-class submarines by about 10 years. These submarines were originally built to last 30 years. HMAS Farncomb, which is almost 30 years old and was set to retire soon, is now expected to stay in service until 2036.

Australia pushes ahead with submarine overhaul

The refurbishment effort, officially known as the “life of type extension,” was first announced by the Albanese government in 2024. The upgrades are aimed at maintaining Australia’s naval strike capability during the long transition toward nuclear-powered submarines under AUKUS.

Speaking at the Lowy Institute in Melbourne, Marles said the work would begin immediately. “The program will reduce engineering risk by sustaining existing systems where appropriate while continuing to upgrade critical capabilities, including weapons and combat systems,” Marles told the Lowy Institute on Tuesday.

The first overhaul is expected to take around two years. During the broader program, an average of three submarines will undergo maintenance at any one time, while the rest stay with the Royal Australian Navy. Officials expect at least two submarines to be ready for operations at all times.

Engine replacement plans dropped

Australia has also reduced parts of the original modernization plan. Earlier, there were plans to replace diesel engines and generators across the fleet, but those plans have now been dropped.

Instead, the government and ASC Pty Ltd will look at each submarine separately and refurbish existing systems whenever possible. This decision comes after a secret review, reportedly led by former U.S. Navy official Gloria Valdez, found that the submarines could safely keep operating for another decade without replacing the engines. Officials think this new approach will make upgrades faster and keep more submarines available.

“This will see a pivot in our approach that reduces risk, upgrades capability, and maximizes availability for the Navy,” Marles said. The government also plans to focus on newer submarines in the fleet, such as HMAS Rankin, which is already undergoing major maintenance.

This change is another big step away from Australia’s canceled French Attack-class submarine project. Under the old French deal, Collins-class upgrades would have used systems tied to the planned French-designed submarines, but that program was dropped in favor of AUKUS in 2021.

Costs rise as AUKUS transition continues

The submarine extension project will now cost up to $11 billion over the next decade, significantly higher than earlier estimates of $4 billion to $6 billion. The government argues that the earlier numbers did not fully account for the amount of work needed.

Under the AUKUS plan, Australia expects to get its first Virginia-class nuclear submarine around 2032, a second in 2036, and a third around 2040. After that, Australia plans to build five nuclear-powered submarines at home.

“Extending the life of all six Collins class submarines is critical to maintaining that edge as we transition the navy from conventional to nuclear-powered submarines,” Marles added.

Shadow Defense Minister James Paterson criticized the government for failing to explain which upgrades had been removed from the program. “As is often the case, he’s failed to provide the details transparently to the public. Which aspects of upgrades previously planned are now being abandoned? And how much is the Albanese government cutting from the program?” Paterson said.

Marles also used the speech to raise concerns about China’s military expansion and tensions in the South China Sea. “In 2013, China had 77 warships. By 2022, it had 140. In 2013, China had around 15 long-range missiles. By 2022, it had 500,” Marles said.