Defence Minister Marise Payne has been unable to say whether she or Defence Industry Minister Christopher Pyne is considered the "senior" minister in the portfolio.

Senator Payne was questioned in Senate Estimates by Labor's Kim Carr about who held ultimate seniority in the portfolio.

The questions follow the ABC's report that there's been angst within the Defence department and the military about the current ministerial arrangement and confusion over who ranks highest between Senator Payne and Mr Pyne.

"Who is the senior minister?" Senator Carr probed.

"I am indicating that both ministers are Cabinet ministers and it's not a question of seniority," the minister replied.

"Are you the senior minister?" he went on to ask.

"Both of us are members of the Cabinet," she said.

Senator Carr asked further whether the minister was trying to suggest the pair were of "equal rank".

"I am, senator," Senator Payne replied.

Ministerial responsibilities 'to be advised'

Senator Payne has promised to reveal her precise portfolio responsibilities and those of her frontbench colleagues Mr Pyne and Defence Personnel Minister Dan Tehan.

At the moment the Defence website has the responsibilities of each minister listed as "to be advised".

Defence Department Secretary Dennis Richardson has conceded there have been some "hiccups" as a result of the Turnbull Government's ministerial arrangements for the large portfolio, but insists having three frontbenchers share duties is working.

"By and large it's been relatively smooth, there's been the odd hiccup which you would expect in any new arrangement but it has worked pretty well," Mr Richardson told the committee.

Senator Payne has confirmed she and her frontbench Defence colleagues last month received Charter Letters from the Prime Minister outlining their precise responsibilities.

"I can provide a list if you like for myself, for the Minister for Defence Industry (Christopher Pyne), the Minister for Defence Personnel (Dan Tehan)," Senator Payne told the Estimates hearing.

"I don't have it here with me but I'll provide that to the committee in due course."

Earlier, the Defence Minister insisted she and Mr Pyne were handling the large portfolio well.

"When you look across the vastness of the portfolio and you pay some attention to the historical splits that have been made in defence by governments of both hues, I think it's a very logical arrangement and one which is working beautifully," Senator Payne said.

Currently the Defence website says all individual portfolio responsibilities are "to be advised". ( Supplied: Commonwealth of Australia )

Mr Pyne was also pressed on the matter in Question Time, with Shadow Defence Minister Richard Marles directing the chamber to the Department of Defence website.

Mr Marles asked who was the senior minister in the defence portfolio, a question that remained unanswered.

Amid a shout of "who's the boss", Mr Pyne responded that the matter was "trivial" compared to what the Department was dealing with.

"Our Defence Force is serving in combat in Syria and in Iraq," he said.

"We have troops in the Middle East, in Afghanistan taking part in serious operations, members of the air force, members of our command who are putting their lives at risk. The only question that the Shadow Minister for Defence can think of to ask me, the first question ever he can think of to ask me is such a trivial matter."