Twenty-four firearms and thousands of rounds of ammunition have been seized in a joint operation between the National Crime Agency and the Police Service of Northern Ireland.
The investigation commenced following the interception of an AR-15 semi-automatic rifle and two hand guns by Border Force officers at an international parcel hub in the Midlands earlier this month.
Officers recovered the firearms and ammunition haul during a raid at a house in Ardkeen, Newtownards, on Friday morning.
The 61 year old man, who lived at the property and is a registered firearms holder, was arrested and released under investigation.
NCA Branch Commander David Cunningham said: “This operation is an excellent example of the cooperation between the NCA, PSNI and our Border Force colleagues. Together we have identified and recovered a significant quantity of illegal firearms and ammunition that could have been used to commit serious violence or other criminality.”