The report from the Government Audit Office said: "Performance on VCS [Virginia-0class submarines] construction continues to degrade. The program now estimates construction of each Block V submarine will take an average of over two years longer than reported last year. The delays are due to problems meeting original staffing and work efficiency estimates.

Block V is the most recent version of the nuclear-powered, attack submarines capable of performing multiple missions and including enhanced undersea acoustic improvements.

"Due to delays, program officials are developing a new, more realistic schedule for Block V. They said that they expect to complete this process in early 2023," the audit, the 21st annual review of the Department of Defence's weapon system acquisition, said.

"Program officials stated that the shipbuilders do not have sufficient workforce to complete VCS while also constructing the Columbia-class submarines and overhauling several Los Angeles-class submarines. They noted VCS construction is about 25% below staffing needs as of September 2022."  

Australia announced a plan in September 2021 to buy two or three nuclear-powered Virginia-class submarines from the US by the early part of the 2023s and then build 10 or 12 submarines along with the UK, with the latter to form the bulk of the country's submarine fleet.

The Virginia-class submarines are needed to fill the void between the retiring of the Collins class submarines and the arrival of the new fleet, with the latter expected to be delivered only in the 2050s or even later.

But the US has been barely able to provide VCS submarines to meet its own needs. It needs new boats in order that it can sell second-hand boats to Austraila.

Additionally, the price of these defence assets may increase, according to the audit report.

It said: "In an effort to improve VCS construction, shipbuilders are outsourcing certain work that they would have otherwise completed in their shipyards, noted program officials. The officials told us that the shipbuilders implemented these changes due to shipbuilders’ workforce constraints and the limited physical capacity of some facilities.

"The same factors that delayed the schedule also contributed to cost increases. While the fixed price incentive contract set target and ceiling prices for each submarine, program officials reported that the VCS shipbuilders have not met the work efficiency and material cost estimates that informed the target pricing.

"Consequently, the Navy plans to request more funds to complete Block V, as its prior budget requests covered the target prices, but not up to the ceiling prices."

In an introduction to the audit, the GAO said: "The Department of Defence continues to face challenges quickly developing innovative new weapons. These challenges persist even with recent reforms to its acquisition process intended to help deliver systems to the warfighter in a timelier manner."