Work has already begun on early stages of the Memorial's $498 million expansion project, which will allow for modern conflicts to be marked and for quiet areas of reflection.

The scale of the project and its price tag have attracted staunch opposition, as has the demolition of Anzac Hall, which will make way for new exhibition space able to house military vehicles and aircraft.

Former directors Brendon Kelson and Steve Gower have listed a series of concerns in submissions to the parliamentary Public Works Committee, including in the size of the proposed works, and the need for the spending.

Retired Major-General Gower said the proposed development would do away with the vision of the memorial's founder CEW Bean for a building that wasn't "colossal in scale, but rather a gem of its kind".

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"It is giantism that could well swamp and destroy the inherent well-recognised heritage value of the site if executed as currently proposed," he said.

"It seems heritage issues have been ignored or dismissed by those responsible for safeguarding the unique intrinsic heritage value of the overall site."

Mr Kelson has likened the proposed new underground entrance to an "upmarket shopping mall".

A collection of historians, academics and former public servants have also made a joint submission against the development, saying it will destroy its character and affect its heritage status. They said a feed of current Defence Department activities would be "totally inappropriate".

However, the memorial's former assistant director, Tim Sullivan, made the case for the changes, arguing the current design of the institution makes it difficult for the public to engage with its spaces, and that a third of visitors do not even visit Anzac Hall as they can't find it.

Mr Sullivan said the proposed expansion would be a "long-term solution to the problems the AWM has had to deal with increasingly since it opened in 1942".

The orientation of visitors at the memorial was inadequate for visitors, both those who wanted a short visit and those who want a more detailed experience, he said, with staff spending time overcoming the difficulties posed by the building's layout.

"Too much staff time is absorbed in directing visitors with research inquiries to the Research Centre or Reading Room as navigation to those places is too complex," Mr Sullivan said.

"Likewise, too many visitors do not find the temporary exhibition space which is obscured behind stairs.

"There are too many choke points where visitors are not presented with clear sight lines to exhibits or programs and so they miss them."