I am willing to stand corrected by those more knowledgeable on the board, but as far as I know there are currently no Air Corps assets assigned a "Rescue" callsign. Certainly in the past there were (Dauphin DH248 had been operating as Rescue 111 prior to her crash in 1999). I suspect that since the Air Corps do not provide SAR directly, and operate in a support role, that is the reason for no call sign allocation.
This may be slightly out of date, but I believe these are the current SAR assets
Rescue 115 - EINN - CHC Helicopters Sikorsky S61N EI-RCG (or EI-CZN spare)
Rescue 116 - EIDW - CHC Helicopters Sikorsky S61N EI-EMS
Rescue 117 - EIWF - CHC Helicopters Sikorsky S61N EI-SAR (or EI-CNL spare)
Rescue 118 - EISG - CHC Helicopters Sikorsky S61N EI-CSX
Charlie 252 - EIME - Irish Air Corps Casa 235 252
Charlie 253 - EIME - Irish Air Corps Casa 235 253
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