Mario Habulin pleaded guilty to six charges, and was the only man involved in all three cocaine importations, described as the principal operative on the ground in New Zealand.

Four members of an international drugs syndicate that attempted to smuggle $20m worth of cocaine into New Zealand have been sentenced to prison terms ranging from 27 to 14 years.

​The men, a Serbian, a Croat and two Australians, were sentenced at the High Court in Rotorua on Tuesday for the audacious plot that involved submersible scooters, gym bags stuffed with cash and the use of container ships as unwitting drug mules.

It remains the biggest seizure of cocaine in New Zealand history and, it was revealed in court, was the syndicate's third importation into the country.

Croatian Mario Habulin was sentenced to 27 years and six months, Serbian Deni Cavallo was sentenced to 23 years and Australians Matthew John Scott and Benjamin Northway received sentences of 24 years and eight months and 14 years and nine months respectively.

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Sentencing judge Justice Grant Powell declined to set any minimum periods of imprisonment when the four appeared in the High Court in Rotorua on Tuesday, meaning each defendant will be eligible for parole after serving one third of their sentence.

That will see Habulin eligible for parole in nine years and two months, Scott in eight years, Cavallo in just under eight years and Northway in just under five years.

MATT SHAND/STUFF Police found 46 kilograms of cocaine at a Mount Maunganui property rented by Matthew John Scott, who the judge described as key player trusted to look after drugs and money.

At an earlier hearing Habulin, 48, and represented by Maryanne McCarty, pleaded guilty to six charges including importing a class A drug, supplying a class A controlled drug, money laundering and participating in an organised criminal group.

Cavallo, 47, plead guilty to importing a class A drug and participating in an organised criminal group.

Scott pleaded guilty to two charges of supplying class A drugs, one charge of money laundering, one charge of importing a class A drug, one charge of participating in a criminal group, one charge of possession of a class A drug.

Northway pleaded guilty to three charges of possession of a class A drug for supply, one charge of participating in a criminal group, one charge of importing a class A drug.

A cultural report cited by Justice Powell revealed Habulin "took a dim view of the New Zealand prison system compared to the French prison system".

Powell, however, dismissed Habulin's concerns cited in the report, including that he would not be able to access education while in prison and run ultra-marathons, as he had in the French system.

MATT SHAND/STUFF Deni Cavallo, pictured at an earlier hearing, played a "significant" role in the offending and traveled to South America ahead of the importations.

"All four have come to New Zealand for the sole purpose, by their actions, to inflict harm on the state and the community," he said.

"It seems almost arrogant to say once they are caught on that endeavour they are entitled to a discount because they don't want to be in prison in New Zealand."

Ron Mansfield, acting for Scott, then addressed Powell and sought to limit his client's involvement.

"He was just holding it at his property. . . that's what the evidence establishes," he said.

"Do you have the leaders and kingpins before you, no you don't."

When Mansfield suggested a starting point of 20 to 22 years imprisonment, Scott sunk his head into his hands.

MATT SHAND/STUFF John Northway (right) was described as the least culpable of the group, providing encrypted phones and security assistance.

Lawyers for both Cavallo and Northway both mooted similar defences, arguing their clients were small players who had no leadership roles in the syndicate.

"A lackey, essentially there as a helping hand," is how Bruce Hesketh, Northway's lawyer described his client.

In his summing up Powell said New Zealand was a desirable market for cocaine suppliers, "and it is important New Zealand not be seen by international syndicates as a soft touch".

He also described the offending as "large scale, wholly commercial, well planned and extremely sophisticated. . . and intended to continue on an ongoing basis."

"This was drug offending at the highest level."

MATT SHAND/STUFF The $20 million operation involved using Maersk Line ships travelling the South Pacific Express service in which underwater caches would be stashed and later retrieved by divers under the cover of darkness.

In a statement issued after the sentencing, Police and Customs said the cocaine seized was intended for New Zealand users and would have caused significant harm.

"The arrests of these four men dismantled a trans-national crime syndicate that was seeking to profit from that harm," said Police Assistant Commissioner for Investigations Richard Chambers.

The operation - in which the syndicate retrieved cocaine from a hidden compartment on the outside of the hull - was sophisticated, Customs Investigations Manager Bruce Berry said.

Police and Customs uncovered the plan with perseverance, he said, sharing knowledge and piecing together information, starting from a simple lead.

Cocaine, container ships and covert surveillance

The men's plot came undone in November 2017 when 46 kilograms of cocaine, with a street value of around $20 million, was seized in a dawn raid in Tauranga.

The 25-page police summary of facts also shines a light on the global nature of the cocaine underworld, with the plot to target New Zealand involving South American cocaine, Vietnamese money launderers and smugglers from Europe and Australia.

The summary also revealed the men were under Police surveillance from August 2017, with electronic devices recording conversations in cars and apartments across New Zealand as part of the Organised Crime Group's Operation Heracles.

In one bugged conversation Scott and Habulin discussed options for sourcing cocaine from South America, noting "Venezuela and Columbia were too dangerous, and that Peru, Panama and Ecuador were all options".

123RF.COM Police seized 46 kilograms of cocaine, worth $20 million.

Their operation involved using Maersk Line ships travelling the South Pacific Express service carrying the drugs in underwater caches that would be stashed and later retrieved by divers under the cover of darkness.

The ships would travel through Mexico, Panama, Colombia, Peru, with the last stop before Tauranga being San Vicente, Chile.

Shortly after each ship left San Vicente, Habulin and Cavallo would travel to New Zealand.

They would pose as theme park owners and theme park engineers when giving their reason for visiting New Zealand to customs.

Habulin is said to have used scuba diving equipment to swim up to the container ships, climb up the rudder and into a cavity to retrieve the drugs before being picked up by Scott and Northway who were waiting on a rented boat posing as fishermen.

Police followed the group while they conducted the operation and the next morning searched a Mount Maunganui address where 46 kilograms of cocaine wrapped in green, silver and brown tape was located. Scott's Auckland residence was also searched which uncovered cocaine and $623,627 in cash.

Police say Scott spent the month of October in negotiation with an Australian company to purchase a "Seabob", a high-end electric underwater scooter designed to explore seabeds to use in the drug collection process.

"He [Scott] was insistent the colour be resprayed to be black," the summary of facts revealed.

CHRISTEL YARDLEY/STUFF Donna Grant was sentenced at the High Court in Rotorua on Friday.

Scott paid an additional $2000 to ensure delivery was on time and discussions were intercepted that revealed the Seabob was to collect cocaine from the Maersk Antares which was due to arrive in Tauranga on October 31.

Money was being laundered through a a Vietnamese money laundering service with Habulin said to be seen taking hundreds of thousands in cash stashed in a gym bag for laundering.

On one occasion he is said to have entered an Auckland gym carrying a large blue canvas bag containing $398,000, which he handed to a woman.

"Police observed the bag was very heavy and the woman struggled to carry it," the summary of facts said.

On another occasion, Habulin was said to have entered the gym with a large duffle bag containing $500,000 in cash.

*This story has been corrected to reflect that Habulin's cultural report was cited by Justice Powell at sentencing, not Habulin's lawyer Maryanne McCarty. Stuff apologises to Ms McCarty for the error.