The New Zealand Defence Force has helped in the seizure of 400kg of heroin, worth about $220 million.
A New Zealand Air Force Orion surveillance plane was on patrol as part of the Combined Maritime Forces (CMF), when it spotted two ships believed to be bound for Africa and Europe.
The French ship FS Surcouf tracked down the ships and found 200kg of heroin stashed on each.
Commander Joint Forces New Zealand Major General Tim Gall said the crew provided vital information that led the French to the heroin, believed to be heading to Africa or Europe.
"This operation has dealt a serious blow to organised crime and terrorist organisations that rely on illegal drugs to fund their activities," he said.
Acting on information provided by the Orion, the Surcouf boarded the first vessel on April 28 and, during a four-day search, found 200kg of heroin stashed in several areas of the vessel.
Surcouf then tracked down the second vessel and boarded it on May 3. Another 200kg of heroin was found.
The New Zealand Orion helps comb more than 6.4 million sq km of ocean, including the Red Sea, Gulf of Aden, Indian Ocean and Gulf of Oman.