Heavily armed officers swooped on the suspects as the Dublin-based gang prepared to storm a firearm dealers shop at Rahan, near Tullamore, Co Offaly, at 7pm yesterday.
Apart from the weapons, detectives also seized a stolen van -- the getaway vehicle -- and a can of petrol which they believe was to be used to set it on fire.
Balaclava, helmets, wigs and gloves were also recovered in the operation.
It is understood that some of the arrested suspects have links to a prominent dissident Republican political party that were involved in protests against Queen Elizabeth's visit last year. The suspects are being held at Tullamore, Mullingar and Lucan garda stations.
At least two members of the arrested gang have barely any previous convictions but are well known to gardai because of their links to dissident Republicanism and are understood to be "politically active".
Gardai have welcomed last night's operation as it has emerged that there were 250 shotguns and handguns in the 'The Tackle Shop', which is run by highly respected local man Jim Griffin.
"If these weapons ended up on the streets, it could have caused mayhem.
"Gardai believe the gang targeted that shop because of its very rural location," a source explained.
It is understood the dissident gang had the gunshop under surveillance for a number of weeks but they in turn were under surveillance from the Special Detective Unit.
Last night's incident is just the latest attempt by organised criminals to steal weapons from rural gunshops.
In September, two suspects who were arrested by gardai investigating a gunshop raid in Co Wicklow in which 29 firearms were robbed have been released without charge.