When Prime Minister Malcolm Turnbull announced the creation of the massive new Home Affairs portfolio in July last year, he called it "the most significant reform of Australia's national intelligence and domestic security arrangements — and their oversight — in more than forty years".

The announcement of the new portfolio — destined to have Coalition hard man Peter Dutton as its first minister — was greeted with lots of debate about whether the new agency would more closely replicate the United States' Homeland Security Department or the British Home Office.

And there was lots of focus on what the changes meant for Mr Dutton's influence within the Government.

But there was not so much on what the department would do.

Super-department accumulates from across government

It had been announced as part of the Government's response to a review of its intelligence operations.

But the new department was not a recommendation of the review, which was focused on the intelligence agencies rather than operational departments which included border security and other aspects of the Government's operations.

Home Affairs has now been operating for just over five months and it says something about the sheer size of the new department that it took a record two-and-a-half days last week for a Senate Estimates Committee to scrutinise the empire.

The new Department of Home Affairs swallowed up the Department of Immigration and Border Protection. From the Attorney-General's Department, it has taken carriage of national security, emergency management and criminal justice functions.

The Office of Transport Security has been plucked from the Infrastructure Department.

Multicultural affairs has been absorbed from the Department of Social Services.

And from the Department of Prime Minister and Cabinet, Home Affairs has taken control of counter-terrorism coordination and cybersecurity.

The super-department also assumes responsibility for key agencies including ASIO, the Australian Federal Police, Australian Border Force, the Australian Criminal Intelligence Commission and AUSTRAC.

Department head aims for 'third pillar' of security

To understand what drives Home Affairs, it is as important to understand the head of the department, Michael Pezzullo, as it is to understand the political role of Mr Dutton.

The assertive secretary of the mammoth new bureaucracy has a very clear world view and a great capacity to build an empire.

Department head Mike Pezzullo has previously played key roles in Operation Sovereign Borders and Australian Border Force. ( AAP: Lukas Coch )

Mr Pezzullo speaks of creating a "third pillar" in Australia's security apparatus, along with defence and the "soft power" of foreign affairs.

In a speech last year, the widely-read secretary conjured up everything from AC/DC's late frontman Bon Scott to the Hobbits in Tolkien's Lord of the Rings to paint a picture of an emerging "dark universe" which he said is the downside of globalisation.

A former Defence Department official, Mr Pezzullo had been central to the Coalition's Operation Sovereign Borders, which played hard on the military approach it was taking to asylum seekers when the Coalition came into office in 2013.

There were briefings by ministers flanked by Defence brass and talk of "On Water Operations".

The military approach again came to the fore in 2015, when the Australian Border Force was established after the merging of the old Immigration Department and Customs Service under the direction of Mr Pezzullo.

Bureaucrats who had sat behind desks all their careers now had to don paramilitary uniforms.

A stronger centre and a clearer picture

Mr Dutton says the advantage of the new structure is that "I think it gives better vision across each of areas that wasn't there before".

Previously, he says, "there was the ability for agencies to work together on particular issues or jobs on cases, but strategically across the organisation, the heads of those organisations now have a much clearer picture about the opportunities and some of the ways in which they can work and align more closely".

Peter Dutton became Australia's first Home Affairs minister five months ago. ( ABC News: Ian Cutmore )

One of the authors of last year's Intelligence Review, Michael L'Estrange, says that, for he and his fellow author Steve Merchant: "There was one galvanising theme that inspired all of our recommendations, and that was the need for Australian intelligence to become a more genuine national enterprise."

"That is, better linked up and better coordinated to meet successfully the evolving challenges of the 21st century.

"We recommended that goal of a genuinely national enterprise be achieved in two ways: one was a stronger centre which would make the whole, greater than the sum of the parts."

Mr L'Estrange said the Home Affairs Department "was not a product of our review, but it was an extension of the principle that was expounded about a stronger centre, building on proven strengths".

"It is one of the biggest machinery of government changes we've seen in Australia in many decades," he says.

"It will take some time to bed down, but I think those principles of a stronger centre and building on proven strengths within a federated system, is actually a sensible way to go."

Concerns around reduced contestability and 'securitising' policy

Peter Jennings from the Australian Strategic Policy Institute says he was initially cautious about the idea of redesigning the Canberra public service "from a series of entities that had worked pretty well".

"I think where I've changed my position a bit since that time has been to see the identified new areas of work that the Home Affairs Department is going to deal with in terms of cyber security, in terms of protection of critical infrastructure", he says.

However, John Blaxland from the ANU Strategic & Defence Studies Centre says: "I would put to you that it's about reduced contestability, and while there are very good people doing the good work, the system will not encourage them to think outside the box and to challenge a view that they may not agree to."

The ANU's John Blaxland says the super-department is "securitising a space that is about more than security". ( ABC News )

The question is over the long run, will this have a corrosive effect, and that's open to debate.

Mr Dutton says, "we've deliberately kept the agencies with their own autonomy but brought them under the umbrella of Home Affairs, so they still have their policy formulation, they still have the ability to test ideas, to almost in some cases have a competitive tension against each other, which is a positive thing".

The department also has a hand in cultural issues, such as "defining Australian values" through citizenship tests, and the economics of population policy.

Analysts have concerns about the "securitising" of areas of policy outside the immediate national security space.

Professor Blaxland says that "one of the concerns that pundits have about the Home Affairs construct is that it is securitising a space that is about more than security".

"It's about how we live, how we identify ourselves, what we see as our future," he says.

But Mr Dutton says: "Our priority in terms of trying to address cultural issues and at the same time making sure that we're running our immigration program in our country's best interest, in our national security's best interest — I don't think they're incompatible."