Australia has charged nine men over an alleged conspiracy to bring in 3.5 tonnes of cocaine and methamphetamine by sea and distribute the drugs nationwide, concluding an almost 10-month investigation by federal and state authorities.

The alleged smuggling operation came to light last May when a commercial trawler sank off the Victorian coast at Port Albert. Police officers monitoring the crew’s movements noted they had travelled out to sea in bad weather without standard fishing equipment, raising suspicion about the purpose of the voyage. In the following months, police conducted surveillance of several boat crews suspected to be linked to the syndicate.

The group allegedly made multiple attempts to reach a drop zone in Bass Strait where smaller vessels would have collected large quantities of drugs from a “mother ship” travelling through Australian waters. All attempts failed and no drugs were brought onshore.

The nine men, aged between 31 and 72, were arrested following raids in Victoria and Sydney.

They face charges including conspiracy to import cocaine and trafficking methamphetamine as well as firearms offences. Seven face the possibility of life in prison if convicted. The eight Victorian men are due in court on 28 July and the Sydney man on 20 May.

Four men were also charged in connection with a separate seizure of 30kg of methamphetamine in Perth last August and 41kg of cocaine in Victoria days later.

The syndicate allegedly used their connections in the trucking industry to move drugs between states.

AFP detective superintendent Ray Imbriano said at-sea drug transfers were dangerous and put both criminals and emergency workers at risk.

“At-sea transfers are dangerous, and criminals using this smuggling method risk both their freedom and their lives,” he said. “It also risks the lives of first responders who too often have had to save the lives of crew involved in drug retrieval.”

He said organised criminals were targeting Australia because of an “insatiable” demand for illicit drugs and the community’s willingness to pay high prices, warning that drug importations fuelled gang violence that left “innocent Australians caught in the crosshairs”.

Victoria Police superintendent Dave Cowan said Australia had become a “favourable location” for organised crime syndicates.

“The damage caused by the use of illicit substances ripples throughout the community, and it does not just affect those using the drug,” he said. Victoria Police said the investigation was ongoing and further arrests had not been ruled out.