The US Navy has abruptly suspended submarine repair work at four West Coast dry docks, prompting fresh concerns about the AUKUS agreement just weeks before Australia, the United Kingdom and the United States announce an "optimal pathway" for Australia to develop nuclear-powered submarines.
The Navy announced over the weekend that it would "temporarily suspend" operations at three docks at the Puget Sound Naval Shipyard near Seattle in the state of Washington, as well as at a fourth dock at the nearby Trident Refit Facility, citing the need to strengthen them to deal with potential future earthquakes.
"The recently conducted seismic assessment, executed as part of the Navy's long-range Shipyard Infrastructure Optimization Program (SIOP), identified potential issues associated with the remote possibility of a large-scale earthquake occurring simultaneously with a submarine maintenance availability," the statement said.
"With this new information, the Navy is taking additional measures to further ensure the safety of the shipyard workforce, Sailors, the local public, the environment, and the submarines."
The US Navy statement does not explain exactly what the "potential issues" are, what work is required to fix them, or the likely cost.
Vice Admiral Bill Galinis, commander of Naval Sea Systems Command, said the Navy would "begin implementing these mitigations immediately and safely return our dry docks to full capacity as soon as possible" but did not say how long operations might be suspended for.
The Navy stressed that the decision "does not affect the nation's strategic deterrent capability or the ability of the fleet to continue its overall mission."
But the closure will still make it harder for the US Navy to field, maintain and then decommission nuclear-powered submarines, and could stir renewed concerns about the constraints which the US industrial base is grappling with ahead of the AUKUS announcement in March.
The United States is already struggling to meet its own Navy's requirements to build two new nuclear-powered submarines every year, while more than one in three submarines in its existing fleet is currently in maintenance or waiting to undergo maintenance.
While the three AUKUS nations have not yet laid out how they will develop nuclear-powered submarines for Australia, there has been speculation that the United States will potentially sell or transfer or sell Virginia-class submarines to Australia to help it bridge the "capability gap" which will emerge when the current fleet of eight conventional-powered Collins-class submarines are progressively retired.
Late last year two high-profile US Senators wrote to President Joe Biden warning that taking that step could push the US industrial base to "breaking point" – drawing a forceful response from a bipartisan Washington lawmakers who threw their weight behind Australia and AUKUS.
In August last year a senior US Navy officer also said that building extra submarines could place an unsustainable burden on American shipyards.
And in recent days a report from the Congressional watchdog has also highlighted problems with the Navy's future Columbia-class submarine program, finding it "lacks essential schedule insight" amid construction challenges.
The latest development comes as Foreign Minister Penny Wong and Defence Minister Richard Marles prepare to meet their British counterparts in the UK for annual talks which are likely to focus heavily on the AUKUS pact and the approaching nuclear submarine announcement.
After that Mr Marles will head to the United States to meet with Defence Secretary Lloyd Austin for high level discussions ahead of the March joint announcement.
Former Senator and submariner Rex Patrick told the ABC that the US Navy's decision to suspend operations at the West Coast dry docks highlighted the strains facing the US system and the vast risks inherent in Australia's ambitious push to build nuclear-powered submarines.
"The US Navy have made no secret of the fact that its submarine build capacity is not meeting US Navy's demand. This news just makes things worse," he said.
"No matter how much talking US Congressmen and Australian MPs do, their words won't change the mounting risks that are building in US and Australian submarine construction yards."
