Stolen plant machinery worth one million euro has been seized, gardai said.
Tractors, excavators and mini-cranes were among the machinery recovered near Balbriggan, north Co Dublin.
It is believed some of the equipment was stolen in England this year.
Detectives from the National Bureau of Criminal Investigation's Stolen Motor Vehicle Unit raided lands and warehouses near Balbriggan at around 8pm on Friday night.
Gardai from Laytown in Co Meath provided back up for the operation.
Fifteen plant machinery units were discovered.
A Garda spokesman said: "No arrests have been made and investigations are continuing."