The captain and first officer of tugboat MV Hamal were yesterday found guilty of drug trafficking.
It had left Turkey for Guyana in South America where drugs were loaded.
In April 2015, after a tip by French authorities, Royal Navy and Border Force vessels boarded the Hamal 100 miles off Aberdeen.
In port it took three days to find all the drugs.
Charges at Glasgow high court against four crew were not proven. Three others were cleared earlier. Mumin Sahin and Emin Ozmen will be sentenced next month.
The Border Force said: “We are protecting communities from harm these drugs could have caused.”
Two men have been found guilty of smuggling more than three tonnes of cocaine - the biggest Class A drug haul in British history.
A captain and first officer were found guilty of drug trafficking after cocaine with an estimated street value of £512 million was seized from their tugboat.
The class A drugs were found hidden in a secret hatch on board the Tanzanian flagged MV Hamal in April last year.
The vessel was intercepted by Royal Navy destroyer HMS Somerset and Border Force cutter HMC Valiant in the North Sea around 100 miles off the coast of Aberdeen.
After getting a tip-off from French authorities, National Crime Agency (NCA) officers boarded the MV Hamal and escorted it into the Port of Aberdeen.
It was the biggest ever seizure of class A drugs in the UK.
When the MV Hamal arrived in port, cutter crew, specialist Border Force deep rummage teams and NCA and Police Authority forensic teams started a search.
Ballast tanks were pumped out for access, and after drilling through a metal panel inside a tank they found a white powder on the drill bit which later tested positive for cocaine.
Investigators soon found an area of floor that had been cemented over in crew quarters, under a medical cabinet.
Inside, there was a sealed metal hatch holding 128 bales of cocaine each weighing 25kg.
The total weight of cocaine on the boat was 3.2 tonnes and its purity was between 58 and 74 per cent.
Investigators believe it had been cut three times over before being sold, meaning it had the potential to create almost ten tonnes of adulterated street level purity cocaine, valued at around £512 million.
Nine Turkish crew members were detained and formally questioned in Aberdeen.
The boat had sailed from Turkey via Tenerife in the Canary Islands and then across the Atlantic to Guyana in South America.
It is believed the drugs were loaded onto the boat when the vessel paused for 12 to 15 hours after leaving Georgetown, Guyana.
Following a 12 week trial at the High Court in Glasgow, chip captain Mumin Sahin and first mate Emin Ozmen were found guilty of two counts of drug trafficking.
Charges against four crew members were found not proven, while three others were acquitted earlier in proceedings.
Sentencing will take place on August 12.
NCA senior investigating officer John McGowan said: “This seizure was unprecedented in scale, the biggest ever class A haul in the UK, and we believe the biggest ever maritime seizure of cocaine in Europe.
“While we suspect that the end destination for this load would have initially been mainland Europe, there is no doubt given the size of the seizure that a good percentage would have ended up being sold in the UK and fuelling further criminality.
“Our investigation has been truly international and we have relied on support of law enforcement colleagues across the globe, including France, Turkey, Guyana and Tanzania.
“I would like to pay tribute to the assistance we have received from the Royal Navy, Border Force, Police Scotland, the SPA and the Crown Office in making this seizure and putting those responsible before the courts.”
Tony McMullin, Regional Director, Border Force North Region said: “The skill and expertise of Border Force search teams are world-leading and this was one of the most intricate concealments we’ve ever encountered.
“Once discovered, it took nearly three days for the team to remove all the cocaine bales from Hamal - demonstrating the scale of the this operation and the ability and dedication of our officers.
“We work closely with law enforcement colleagues in the UK and around the world to protect the security of our border.
“By preventing drug trafficking and putting those responsible behind bars, we are also protecting our communities from the harm these drugs could have caused.”