The CIÉ 121 Class locomotives (or yanks as railfans called them) were built in LaGrange, Illinois by EMD in 1960. They drastically improved CIÉ's rail services as they were far more reliable and far more economical than their Metropolitan Vickers 001[A] and the 201[C] class locomotives. These single cabbed "Road-Switchers" were a lightweight version of the SW900 with road trucks.
Unlike their American equivalents these locomotives were not permitted to run bonnet first as the driver's view was poor in this direction.
They were mechanically similar to the later 141 class locomotives, the main difference between the two was that the 141 class locos had two cabs. they used different traction motors and lacked multiple working capability(later fitted).
They were capable of 77 m.p.h. They were shipped with EMD 567 engines but these were later upgraded with 645 power packs retaining the same engine blocks. Their original 567s were capable of 960 b.h.p, the 645s fitted later were capable of 1100 b.h.p.
The last two locomotives, 124 and 134, are owned by the Irish Traction Group and the Railway Preservation Society of Ireland respectively.
124 is stored under a tarpaulin in Moyasta Junction, and 134 is stored at Inchicore works In Dublin.