Four pipe bombs, a sawn-off shotgun and heroin has been found hidden down a manhole beside a derelict house.
Gardai involved in targeting organised crime in Co Louth made the discovery during searches of land around the property near Castlebellingham on Thursday evening.
The shotgun had been buried with several cartridges while the pipe bombs have been described as viable.
Some 45,000 euro of heroin, packaged and wrapped for sale on the street, was also hidden in the underground cache on land in the Kilsaran area.
Gardai said that other material used to make pipe bombs was also recovered from the manhole.
The Army bomb squad was called in and spent several hours making the pipe bombs safe. A technical examination was carried out and the devices have been removed for technical and further forensic examination.
The investigation is ongoing, gardai said.