Rainbow Warrior saboteurs carried out practice missions before bombing Greenpeace's flagship in Auckland 30 years ago, according to sources in France.
It is also claimed that the second in command of France's spy service, the DGSE, personally visited New Zealand before two explosions sank the ship at Marsden Wharf, killing photographer Fernando Pereira.
Autobiographies by Alain Mafart and Dominique Prieur, by veteran French DGSE operative Bob Maloubier, who died this year, investigations by journalist Jean Guisnel and other sources have exposed details of the mission and its run-up and helped to put real names to aliases. Among the revelations is that DGSE's combat divers carried out sabotage operations that helped provide a blueprint for the attack.
One was on August 14, 1980, knocking out a transmitter on Monte Capane, on the Italian island of Elba, that was used by Radio Corse Internationale, a pirate radio station challenging French policy over Corsica.
It honed skills in infiltrating agents into a friendly country and extricating them by sea.
A second was in 1982 when DGSE combat divers disabled a ship carrying a Libyan arms shipment off the coast of Genoa, Italy.
French sources also say that General Roger Emin, the chef du service de la recherch and number two at the DGSE, went on a reconnaissance mission to New Zealand, on the orders of his boss, Admiral Pierre Lacoste.
Lacoste had grave doubts about the scale and distance of the operation, which had been ordered by the autocratic defence minister of the time, Charles Hernu.
Lacoste trusted Emin, who had witnessed French military debacles in Indochina and Algeria, to see if the scheme was feasible.
The plan changed from placing a small charge on the ship's propeller shaft rather than on the hull, given the risk that shrapnel and flooding posed to anyone inside the ship.
Seeking to find the most effective spot that posed least danger, the DGSE acquired the drawings of the Rainbow Warrior and even carried out tests in the Mediterranean to ensure that the crew cabins in the aft of the ship would not be hit by shards.
But things changed in mid-April, when the order came that the ship was to be sunk in a spectacular but still non-lethal message to the nuclear protest movement. A second bomb was to be placed on the hull.
Many in environmental groups regard French claims that the saboteurs tried to avoid causing death as propaganda and point to factors such as that no warning was given, the blasts were at night and the bombs were designed to rapidly sink the ship.
"No one will believe that a bomb placed on the side of our ship, in the middle of a cold winter night, while most people were sleeping on board was a warning," outgoing Greenpeace New Zealand executive director Bunny McDiarmid told the Weekend Herald. "The bomb blew a hole the size of a truck at our waterline and sank the Warrior in four minutes. A bomb is not a warning. The French agents were certainly incompetent but the suggestion that the first bomb was supposed to be a warning is cowardly and insulting and doesn't change the fact that they remain guilty of murder."