"Civilian radar does not see the aircraft but rather the transponder code and if the transponder is turned off then Shannon would not be able to find the aircraft."
Only true for SSR radars - Ireland has 3 PSR radars in the three airport.
Radar coverage of the airspace, for which the Irish Aviation Authority is responsible, is provided from: seven Monopulse Secondary Surveillance Radar (MSSR) Sensors and three Primary Surveillance Radar (PSR) Sensors, located at Dublin Airport (two co-located MSSR/PSR), Cork Airport (PSR), Mount Gabriel (two MSSRs), Co. Cork, Shannon Airport (co-located MSSR/PSR), Woodcock Hill (MSSR) Co. Clare, and Dooncarton (MSSR) Co. Mayo. Each MSSR Sensor is equipped with a rotating radar antenna, and dual interrogators, receivers, extractors and trackers. I believe that all MSSR traffic is transmitted over data lines to the Air Traffic Control Centres (Shannon, Dublin, Cork).