Operation Beech kicked off in November after Drug Enforcement Administration agents seized a record 2.4 tonnes of cocaine allegedly bound for Australia off the South American coast.
Police say the shipment was linked to a Mexican cartel and traffickers had no idea of the seizure, believing the drugs were still on their way to Australia.
Police learned the alleged Australian arm of the group was waiting to receive the haul about December 28, prompting Western Australia officers to put together a dummy package using an inert substance.
They dropped the parcel off about 40 nautical miles west of Perth's coast and over three days to December 30, a shore party allegedly made three trips out to retrieve the package because they couldn't find it.
The party rode out in "uncomfortable conditions" in two vessels, Catalina and Cool Runnings - both of which ran into trouble.
Cool Runnings had issues with steering and washed ashore south of Moore River.
The Catalina crew towed Cool Runnings out to sea and allegedly transferred the inert package over to their vessel. Then, the Catalina sank.
Officers watched their moves from the air and a tactical response group arrested three people aboard Cool Runnings allegedly with about 1.2 tonnes of the inert substance.
Detectives executed search warrants in Perth on New Year's Eve and charged nine men with attempting to possess 1.2 tonnes of cocaine.
Even after the arrests, police say the syndicate still believed the cocaine was available to buy and on January 9 officers raided a property at Carlisle in Perth and arrested a 28-year-old NSW man.
He was charged with attempting to possess 200 kilograms of cocaine.
Then on January 13 police stopped a vehicle on the Great Eastern Highway near Coolgardie, more than 550km east of Perth, and found more than $2 million in cash.
They charged a 39-year-old man and a 37-year-old woman they say are connected to the syndicate.
The covert operation was a joint effort between the Western Australia Police Force's transnational serious and organised crime squad, officers from other states and the enforcement administration.
"This operation has enabled us to draw out those members of the syndicate who were equipped and prepared to receive and distribute a significant amount of illicit drugs within the community, who may have otherwise gone undetected and waited for the next consignment," WA police commissioner Col Blanch said on Saturday.
"The operation sends a message to international drug traffickers: 'Your deadly drugs are not welcome here and we will work closely and innovatively with our on-shore and off-shore law enforcement partners to dismantle your operations.'"
WA police are working with their overseas partners to track down the people who organised the shipment.
The dozen alleged offenders already arrested come from the US, NSW and the Northern Territory.
They are progressing through Western Australia's courts.
