AK-47 assault rifles, revolvers and explosives were among a significant terror arsenal uncovered by Gardai targeting dissident republicans.
The weapons cache was found in a shed and buried on land at Jenkinstown, outside Dundalk, Co Louth.
The search was called off last night, but Gardai will resume the operation this morning and it could last several days.
The search area is less than five miles from the Lordship Credit Union where Det Garda Adrian Donohoe was shot dead by a hold-up gang in January 2013.
More than half a dozen guns were discovered, including a number of AK 47 assault rifles, revolvers and what appeared to be a machine gun.
Officers also seized component parts for mortars and several hundred rounds of assorted ammunition.
The search followed weeks of surveillance and intelligence gathering on suspected members of the Real IRA.
Some of the cache was discovered in a shed adjacent to an occupied house at Jenkinstown, close to Gyles Quay, while part of the arsenal was also found buried in hedges and on surrounding land.
No arrests have yet been made in connection with the finds.
It is the second major cache discovered in less than three weeks in the on-going crackdown on dissidents in the Border region.
Late last month gardai recovered weapons that were believed to have been stolen from the Provisional IRA several years ago.
That cache was found outside Scotstown, Co Monaghan and included eight AK-47 assault rifles, mortars and component for improvised explosive devices.
It's almost three years since Gda Donohoe was gunned down in cold-blood by raiders believed to have links to republicans. No-one has been brought to justice for the brutal murder that took place as he guarded a cash delivery from the credit union.
The five-member gang suspected of murdering Gda Donohoe were identified within days of the killing on January 25, 2013 - yet all remain free, with some having fled the jurisdiction.
Gardai believe that there are several witnesses that could provide evidence but no one has come forward.