The Córas Iompair Éireann 121 Class was a railway locomotive which was manufactured by General Motors Electro-Motive Division. These locomotives were in regular service on the Irish railway network until 2002, with the last two remaining in service until 2008. History The poor availability of the A and C class locomotives in the late 1950s together with the split of the cross-border Great Northern Railway in 1958 and the target to eliminate Steam Locomotives led CIÉ to urgently seek more diesel locomotives, turning to an American-style single cab road switcher design from General Motors. The 121 Class were manufactured from December 1960 to January 1961 and numbered B121 to B135 inclusive. The locomotives proved an immediate success, with low maintenance and high availability, and led to further orders from the same supplier starting with the 141 class. From the early 1970s onwards several locomotives of this class dropped the "B" prefix from their fleet number when re-liveried. The last two locomotives that survived in traffic (124 and B134) were both withdrawn from service on 3 May 2008. Prior to 1961, almost all Irish diesel locomotives were built in Great Britain, but from the 1960s onwards, GM became the sole supplier of locomotives to CIÉ, which eventually also extended to Northern Ireland Railways locomotives at a later stage. These were EMD's first ever fully American-built locomotives delivered to Europe. The layout of the cab was quite different from the other conventional CIÉ diesel models of the time, with the controls to the side of the driver, rather than the front. Due to apparent driver complaints of reduced visibility when operating with cab trailing, it was ultimately decided that these locomotives should only operate in a cab-leading formation. Later conversion for multiple-unit working allowed two 121 class locomotives to be coupled hood-end to hood-end, removing the need to turn them around for their return journey. Although originally fitted with an EMD 8-567CR engine of , all were later fitted with 645 type "power packs" (piston & liner assemblies) for parts standardisation, while at the same time keeping their original power output for reliability reasons. They weighed and had a maximum speed of . Numbers B126-B129 were later rebuilt with an EMD 8-645E engine of ; as used in the 181 Class locomotives. The engine blocks were originally recycled from withdrawn rebuilt class B201s, but in their later years much swapping of engines