Yes, three bases due to three helicopters. But the choice of the location of those three bases is up to the bidder, and (as you say), there is only a small number of suitably equipped locations to choose from. The more detailed requirements include these four (from a list of 119!)
- any one helicopter can reach any point onshore in Ireland or within 12 nm of the Irish coast in 45 minutes from becoming airborne
- any two helicopters can reach any point onshore in Ireland or within 12 nm of the Irish coast in 60 minutes from becoming airborne
- a helicopter can embark an emergency service team based in Dublin and depart with them onboard at any time of day within 60 minutes of being tasked ‘day’ or 90 minutes ‘night’.
- all bases to have an approved instrument approach available 24 hours a day for the contracted aircraft types based there, with appropriate mitigations where the approach minima is no higher than CAT 1 ILS minima