Defence Chief Mark Binskin will today hand command of Australia's armed forces to Army Chief Angus Campbell, ending a 40-year military career.

Air Chief Marshal Binskin, and Vice Chief of Defence Ray Griggs, will formally hand over command to the next generation of defence leaders, ending a combined 80 years of military experience.

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In his final hours commanding Australia's 80,000 strong Defence Force, Air Chief Marshal Binskin was feeling relaxed.

"One thing I've learnt over the many years in the Defence Force is you can trust the people, the command and control, the processes that are in place and the checks and balances," he told AM.

But he conceded the next defence chief, Lieutenant General Angus Campbell, would have much to juggle.

"The security environment's not getting less complex," he said.

South China Sea concerns

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As tensions rise in the South China Sea, Air Chief Marshal Binskin said there was concern about reports of the militarisation of the area.

He would not rule out Australia taking a more assertive approach in the future to challenge Beijing's claims in the contested waters.

"I won't talk about the specifics of what we will do operationally in the future, or may do operationally — it will depend on the situation," he said.

"But we will always ensure that freedom of navigation is available."

And the outgoing Defence Chief said with regard to North Korea, "we need to go into this eyes wide open".

"We have a leader in the DPRK [Democratic People's Republic of Korea] that mortgaged his country to develop a nuclear capability," Air Chief Marshal Binskin.

"I don't think that is something that he would give up lightly."

Don't put timeline on Afghan mission: Defence Chief

During his time at the top, Air Chief Marshal Binskin has watched Australia's operations in Afghanistan transition from combat to an advise and assist mission.

While he said he was now more optimistic about the war-torn country's future, he believed it was too early for coalition forces to leave.

"The Government's got some good programs in place, they just need support," he said.

He said he expected Australia and its allies would need to remain in Afghanistan for some time.

"And it's important not to put a fixed timeline on it because the Taliban sits there and watches that," he said.