CIE had a few ambulance coaches, created at various dates from at least 1950, or possibly before. They carried their original numbers for a long period, but were renumbered into a special series in the Autumn of 1965. AM10 to 13 were formerly 94M, 163M, 1097 and 1900. They were joined in early 1966 by AM14 and AM15, converted from Park Royals 1380 and 1408. The latter was the driving trailer from the Waterford & Tramore and had been in store since returned to Inchicore, following closure of that line. The extra two were probably there to allow withdrawal of some or all of the earlier coaches. Edit: I see from notes that 1097 replaced 346 about 1957, so perhaps there were other "Invalid" coaches that didn't get re-numbered as "AM".