A professor of politics and international relations has explained how previous governments made decisions that led to New Zealand's military force struggling to retain staff and losing droves of planes and ships.

Documents released under the Official Information Act have revealed workers with critical skills have been departing the force, which means ships are tied up and aircraft can’t fly. Big money payments have been made to keep critical staff in place but one briefing called it “too little, too late".

Talking to Newstalk ZB's Summer Breakfast this morning, University of Auckland professor Stephen Hoadley was asked what, alongside poor pay, was adding to the challenge of keeping staff on board.

"We've got to go back to history and find out why this has all happened," said Hoadley.

"This is not new, this has been coming on for the last two decades at least."

Hoadley said that, back in the early 2000s, the Labour administration in power at the time was provided with a large number of new platforms which had recently been acquired and which required a lot of new personnel, new training and a lot of upgrading.

Among the platforms were seven new ships for the Navy and 105 light armoured vehicles for the Army as well as upgrades for the Air Force. This was the beginning, according to Hoadley, of this personnel crunch.

"It's not a crisis at the moment, it's a difficulty, but it's been building gradually over the years as the tempo of exercises has increased," he said.

Hoadley pointed to the fact New Zealand's relationship with the United States had been restored over the decades and there were more opportunities for soldiers to work abroad, in some cases it was requested by some of New Zealand's allies.

"Then of course came [the Covid-19] pandemic, which reduced training time and a lot of what should have taken place did not take place," he said.

"Then there was the general neo-liberal economic policies of the Roger Douglas era that separated the private sector and accelerated their salaries above those of the public sector including the [armed forces]."

Asked what New Zealand's allies would make of the country's military challenges, Hoadley indicated it was likely they were already well aware of the issues at hand.

He said that, under Prime Minister Helen Clark, her chief of defence force had been continuing to report the growing problem from 20 years back and had shared their views with their counterparts abroad.

"Many other governments are facing very similar problems of retention as their private sectors under the more globalisation, liberalisation policies," said Hoadley.

"They have increased their salaries and outrun the salaries for the public service ... New Zealand isn't entirely alone, I think there will be some forbearance among New Zealand's partners to say 'well it's too bad we're facing a similar problem, and we'll have to somehow work around this'."

Hoadley was pessimistic about the current Government's actions to tackle the staffing issues given there were no defence policies listed in its 100-day plan.

He said by looking at the Cabinet, you could see every minister clamouring for funding in a limited budget for their priorities and Minister of Defence Judith Collins alone has a number of competing priorities, including in her roles as attorney general and her other portfolios.

There is also an advancing challenge with China, Hoadley said, which requires New Zealand to be more vigilant and to increase its patrolling and assistance to Pacific Island nations to strengthen ties.

"This requires more resources, disaster relief of course - in cyclones and tsunamis, that sort of training and other kinds of assistance," he said.

Hoadley pointed to the rising crisis in the Gulf of Aden in the Bab el-Mandeb Strait. Australia had been asked to send a ship but wasn't able to and had instead decided to send diplomatic support.

"This is how New Zealand will respond as well," he said.

"They'll say 'look we may not be able to send the Canterbury, but we can send the Manawanui'. We may not be able to send an aircraft but we can use commercial aircraft or ask Australians to transport us to a troubled spot.

"So, there are ways to work around this personnel shortage."