As the Newcastle Herald reported yesterday, Prime Minister Scott Morrison has been accused by the SA Independent senator and former submariner of "politicising" the Defence Department's planning process by naming Port Kembla, Newcastle and Brisbane as the three short-listed candidates for a new base.

Defence documents from 2011 to 2017 - obtained by Senator Patrick under Freedom of Information, and referred to by Mr Morrison on Monday, repeatedly put Sydney Harbour at the head of its lists, followed by Jervis Bay on the NSW South Coast.

The 2011 planning study considered more than 15 sites, including four in Sydney Harbour, and ranked the various Sydney sites ahead of two at Jervis Bay, followed by Newcastle, Westernport Bay in Melbourne and with Brisbane last of nine.

The other sites were considered but dismissed, with the apparent favourite now, Port Kembla, described as "small and congested with little space for substantial expansion".

"It would be impractical therefore to develop an FSM (future submarine) basing capability at Port Kembla," the 2011 report by Commander D.L. Stevens.

However on Tuesday, Navy responded to Newcastle Herald questions, saying: "Changes in commercial activity at Port Kembla has realised a large pocket of land which is now potentially suitable for creation of a new naval base."

Port Stephens - which as Mike Scanlon has recently reported was considered for a major base a century ago before the navy opted for Jervis Bay - was also looked at briefly, but rejected.

The 2011 report said Port Stephens had been considered but ruled out in a 1992 review of naval locations.

This followed a Hawke government push to move the Navy out of Sydney to Jervis Bay, which was eventually abandoned after sustained opposition.

Although the former BHP steelworks site has been vacant for 20 years, the 2011 report (written before the port was privatised in 2014) described the Eastern Basin wharves as the "primary area of interest", with the adjacent Western Basin of "secondary interest".

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The 11.6m depth was sufficient, as was the land area, and submarine movements would be "manageable" with shipping movements predicted to rise from 3000 annually in 2011 to 5500 in 2020. (Port of Newcastle reported 4600 last year).

The old Carrington pump house stands between the Basin wharves, and Honeysuckle Drive apartment blocks with views to the Basin would "limit the visual security and privacy" of any base.

Cruise ships berthed nearby at the Dyke wharves posed another "visual security" problem but the Hunter had established Defence contractors who could "readily support" a Newcastle base - although in 2011 the intention was for conventional rather than nuclear subs.

Information from the Defence Department responding to Newcastle Herald questions was used in yesterday's reporting.

However further questions, including the apparent differences between Mr Morrison's short-list and the Navy's preferred options among the 19 seats considered have received no response.

Labor defence spokesperson Brendan O'Connor said the opposition had been kept in the dark about the announcement despite the ALP supporting AUKUS and despite the government having to enter caretaker mode in the coming weeks because of the election due by May 21.

"Despite claiming they would keep Labor updated, we haven't had a single update from the Morrison-Joyce Government on this strategically important decision, which is, quite frankly, appalling," Mr O'Connor, MP for Gorton in Victoria, said.

"Labor calls on the Government to provide a detailed plan in the national interest, not Scott Morrison's political interest as to how it will rectify delayed and over-budget defence contracts."