New Zealand is unable to do major servicing of its new maritime patrol and submarine-hunting planes so is sending the work to Australia.

Australia is building up its sovereign defence industry capabilities that have been run down over the years.

But the New Zealand Defence Force (NZDF) knew when it spent $2.3 billion on its four Poseidons - a match for Australia's dozen - that servicing their high-tech complexity was beyond it.

"New Zealand does not have - and has never had - the organic capability to conduct depot-level maintenance on the P-8A," Defence told RNZ on Thursday.

It also did not help when Poseidon routine maintenance staff numbers fell to half what was needed, in late 2023.

The gulf in servicing capability is likely to grow as AI algorithms for hunting subs, along with extra torpedoes, are added to Poseidons flown by New Zealand's main partners.

However, Defence said sharing a fixit depot with Australia was a bonus of buying the same plane as them, and of the two forces' very close ties.

Australia for its part is counting the benefits of beginning to tool up.

"The servicing will inject up to $160 million into the local economy; and create and sustain 80 highly skilled jobs across Adelaide, supporting local businesses and fostering innovation within defence industry," said its defence force.

The work includes also newly servicing US Navy Triton drones.

The new contracts lined up with the 2024 sovereign strategy, it said.

The strategy states that being able to maintain and overhaul planes was "critical to optimising aircraft availability and ensuring it is not compromised, especially during times of conflict".

Interoperability with Australia and the US is a touchstone for the NZDF, but one that is increasingly stressed by the speed and scale of the rush towards advanced and emerging military technology.

Canberra said the federal Budget this week was putting billions into "cutting edge" defence capabilities.

Here, the Poseidons were called a "once in a generation investment" that form one of just three core high-end capabilities at Defence.

But their delivery since 2022 has coincided with what Defence called the hollowing out of forces as up to 30 percent of staff left in a year.

By late 2023, Poseidon maintenace staff were at just half what was needed long term, and internal reports warned, "Supervisors are the key limiting factor, with contracted civilians temporarily in place. Avionics supervisors are critical."

RNZ is seeking an update on worker numbers.

Defence is now moving to cut over 300 civilian roles.

The Ohakea air base near Bulls is in the middle of an upgrade, and it would do the regular Poseidon maintenance, but extensive inspections, and the overhaul of equipment or systems, required specialised skills and facilities, a spokesperson told RNZ on Thursday.

Australia moved in 2022 to upgrade the air base near Adelaide, under a $70m deal with Boeing.

This would allow Poseidon work to be completed "locally and more efficiently ... that would otherwise have been performed in the United States", it said.

Yet the overall Australian defence workforce actually contracted by 10 percent in 2023 alone.

One means the government was using to try to turn that around is to [https://www.australiandefence.com.au/news/news/losing-the-defence-industry-workforce

do deals with the US and UK under AUKUS], to supplement American weapons-making.

The NZDF's strategy for 2019-25 and 2019 capability plan stressed encouraging big international contractors to use local companies, and forming partnerships "to support the full capability life-cycle" of its planes, ships and other assets.

"To effectively operate and support the new capabilities to the desired potential, the Air Force must enhance its enabling personnel and base infrastructure," the strategy said.

Boeing said three years ago it would build a New Zealand team to support the four planes. RNZ has asked Boeing what work the team is doing.

The NZDF said it was able to share training and personnel with Australia: "The synergies and economies of scale afforded by utilising the same depot-level maintenance facilities" was another bonus.

The old maritime patrol Orion planes, and old Hercules, were easier to service in New Zealand.

The new Poseidons have as many as seven operator consoles and are getting ever-more complex: Australia, the US and UK have already added a common AI algorithm so the three can process data from each others' sonar buoys, allowing for faster target identification.

Next up could be adding Sting Ray light torpedoes, alongside existing torpedoes of another type.

The suite of electronic detection can include radar, and digital electro-optical and infrared multi-spectral sensor. There are so many systems that a plane has its own customised cooling gear.

Boeing is now looking at adding more powerful satellite communications, alongside connections to the US's Wideband Global satellite (WGS) system that New Zealand has helped pay for.