The 001 Class locomotive was the backbone of mainline passenger and freight train services on the Irish railway network for forty years from 1955 until the mid-1990s when they were replaced by the new 201 Class.
Initially they were fitted with eight cylinder two-stroke, port controlled Crossley engines. These were a loop scavenge type, which utilised a patented principle that recycled the normally wasted exhaust-pressure pulse to boost charge air in the cylinder. They produced 896 kW (1200 hp) at 625 rpm and could do 120km/h (75 mph). The original sandboxes, which were utilised to improve traction with the rail, were removed after a few years.
Their Crossley engines proved to be notoriously unreliable from the start. Amongst a plethora of problems were:
These problems were tackled between 1968 and 1971 through the progressive re-engining of the entire class with a 12-cylinder EMD 645E engine (a similar process was implemented for the original 201 Class) However, this power output stressed the ability of the original cooling & transmission systems and the engine output was reduced to for improved reliability. When built, these locomotives were originally numbered A1 to A60, and as locomotives were re-engined, they had the suffix 'r' added to their number. From 1972, the prefix letters were dropped and the locomotives were renumbered 001 to 060.