Gardaí (Irish police) have seized cocaine worth about €2m (£1.7m) during searches in Dublin, Kilkenny, Waterford and Ashbourne, County Meath.
They also found three Glock pistols, a replica handgun, drug-mixing equipment and 1kg of cannabis worth approximately €20,000 (£17,000) during the operation.
Officers intercepted two vehicles in the Finglas area of Dublin shortly before 16:00 local time on Friday.
Four men - aged 22, 27, 32 and 55 - were arrested on suspicion of drug offences.
The equipment uncovered during the searches included a hydraulic drugs press and a quantity of mixing agent.
Officers also seized €18,000 in cash and several communications devices.
Assistant Garda Commissioner Justin Kelly said: "This significant intelligence-led operation conducted by the Garda National Drugs and Organised Crime Bureau, supported by colleagues from Dublin, Waterford, Meath and Kilkenny, demonstrates the inextricable link between illegal firearms and the drugs trade.
"We know that these type of deadly weapons are used by organised criminal groups to intimidate, maim and kill.
"Suppressing access to illegal firearms is an absolute priority for An Garda Síochána.
"I wish to compliment the officers who continue to put themselves in harm’s way, in operations such as this, to protect our communities."