Thousands of New Zealand Defence Force (NZDF) personnel - across the three services of army, navy and air force, and also civilian employees - have left in recent years, chasing higher pay and better opportunities.

In the two years to January, 3228 people exited the NZDF, which had an average headcount of 11,824 at the end of 2023.

That headcount is roughly equivalent to 2015 levels.

The navy suffered the highest attrition, with 17 per cent leaving in the year to January 2023, just ahead of the army, with 16.9 per cent.

Attrition - described by former defence minister Andrew Little as "a big hollowing out" - has hurt the military's deployment capacity.

An key example of this is that four of the Kiwi navy's nine-strong fleet unable to to be staffed.

"It's a real concern that they're not able to be used," Defence Minister Judith Collins told AAP earlier this year.

"When I have questioned Defence about this, it's been attrition basically.

"What we've got to do in Defence is to get that attrition rate down, the morale up and then the mojo back on steroids."

Five months into the job, Ms Collins is seeing progress.

Figures provided to AAP show attrition nearing long-term averages and this year, and for the first time since COVID-19, growth in overall defence numbers.

The total attrition rate was at 15.5 per cent in the year to January 2023, but sits now at 10.6 per cent - just above the decade-long average of 10 per cent.

That has allowed the NZDF to replace the staff it is losing, with headcount up marginally to 11,867 at the end of February.

"But this is not enough," Ms Collins told AAP.

"The NZDF is completely dependent on suitably qualified and experienced personnel to deliver for New Zealand, so it is critical that we continue to work to build back our defence force and support our personnel.

"This is an absolute priority for me as minister of defence."

New Zealand is far from the only country suffering from high attrition rates in its military, with many developed nations including the UK, Australia and Canada all battling to keep trained servicemen and women in uniform.

The overall numbers also hide particularly shortfalls - particularly those with particular technical skills.

Departure of musicians and writers were also running at double the average attrition rates.

Documents released under the Official Information Act showed the key reasons behind departures were opportunities elsewhere and poor remuneration.

The last Labour government moved to bridge the gap between what NZDF personnel were paid and "their market rates" by lifting annual wages for many roles by up to $NZ15,000 ($A13,800).

NZ DEFENCE ATTRITION RATES

Year to January 2023 - Overall: 15.5 per cent

Navy 17 per cent, Army 16.9 per cent, Air Force 11.9 per cent, Civilian 15.2 per cent

Year to January 2024 - Overall: 11.4 per cent

Navy 12.5 per cent, Army 11.2 per cent, Air Force 10 per cent, Civilian 12 per cent

Australian Associated Press