Thirty years after France's deadly bomb attack on the Rainbow Warrior in New Zealand, anger still crackles in Pete Willcox's voice when he discusses the sinking of the Greenpeace flagship.

Willcox was captain of the environmental group's converted trawler when frogmen working for French intelligence slipped into Auckland Harbour late on July 10, 1985, and fixed two large limpet mines to its hull.

Portuguese photographer Fernando Pereira died in the subsequent blasts, which New Zealand's then-prime minister David Lange described as "a sordid act of international state-backed terrorism".

"Fernando had two children and his murder blew a hole in their lives that can never be patched up," Willcox told AFP ahead of the anniversary.

"And as a captain, the worst thing you can do is lose a crew member. It was hard."

The Rainbow Warrior had docked in Auckland on its way to protest French nuclear testing at Mururoa Atoll, about 1,200 kilometres (750 miles) southeast of Tahiti.

But France's spy agency, the DGSE, had other ideas, launching the ominously titled "Operation Satanique" to stop it.

The mission was unprecedented -- bombing a peaceful protest vessel without warning in the territory of a friendly nation.

A former top French intelligence official described it as a "fiasco".

"This type of action against an opponent like Greenpeace would be unimaginable today," he told AFP, speaking on condition of anonymity.

New Zealand journalist David Robie said Paris -- spurred by Cold War paranoia -- believed Greenpeace must be stopped to save the nuclear programme and curb calls for independence from France's Pacific territories, which were being fuelled by the controversial testing.

"It reflected the militarised mindset that prevailed at the time," said Robie, whose book about the incident, "Eyes of Fire", has been updated for the anniversary.

- 'A trail so Gallic...' -

New Zealand police initially dismissed the idea of French involvement as a conspiracy theory, while officials in Paris denounced the very suggestion as a national slur.

They were forced to backtrack two months later as evidence mounted, exposing embarrassing blunders by the DGSE team.

A French-made inflatable boat and diving gear were abandoned in Auckland waters, while investigations into suspects uncovered records of calls to the defence ministry in Paris.

"They left a trail so Gallic that the only missing clues were a baguette, a black beret and a bottle of Beaujolais," a DGSE source told the Washington Post at the time.

Most damningly, two agents posing as a Swiss couple were arrested in the days after the explosion as they attempted to return a rental campervan.

The pair -- Alain Mafart and Dominique Prieur -- were only captured because they were reluctant to flee New Zealand without collecting the NZ$130 ($90) deposit on the vehicle.

The scandal rocked the French government, leading to defence minister Charles Hernu's resignation and the sacking of DGSE chief Pierre Lacoste.

The fallout could have been worse, with Lacoste releasing a memo in 2005 that stated the then-president Francois Mitterrand personally authorised the operation.

- 'They set out to murder us'-

Mafart and Prieur were charged with murder, eventually pleading guilty to manslaughter and receiving 10-year jail terms.

But they were free within three years under a deal that caused almost as much angst in New Zealand as the bombing, involving France threatening to block trade access to European markets unless Wellington handed over the agents.

No one else in the 13-strong DGSE team ever faced justice over Pereira's death.

Robie said the bombing "utterly backfired", outraging New Zealanders, galvanising anti-nuclear sentiment in the Pacific and trashing Paris' reputation in the region for decades.

Public sympathy resulted in an upsurge of donations and members for Greenpeace -- helping it go mainstream -- and Willcox said the attack remained a defining moment in the organisation's history.

"We never believed that a bunch of hippies in an old steel boat would scare the government of France so badly they would set out to murder us," he said.

"Yet they did, and we took it as a sign that we must be doing something right."