They were originally planned for use on the Mullingar to Sligo mail trains, however they were poor steamers and proved to be underpowered for this work being transferred soon afterwards to the Westport – Achill branch line in western County Mayo — a highly scenic line which passed through the small town of Newport and the village of Mallaranny before reaching the western seaboard at Achill Sound.

Following the absorption of the MGWR into the Great Southern Railways in 1925, they were renumbered 534, 535, 531, 532, 530 and 533, in the same order as the original numbers shown above.

It was the intention that these conversions would replace the Class K, 2-4-0 [citation needed] locomotives but with their steaming problems the Ks were still in service long after the last D had been relegated to minor duties or even the scrapheap.

Following the closure of the Achill line in 1937, there was little work for them to do, but one served on the Claremorris to Ballina branch for a time, another was occasionally used between Portarlington and Athlone and a third member of the class ended its days as a stationary boiler at Broadstone depot.

[1] Redesignated as the Class 530 or Class D16 by the Great Southern Railways, and repainted overall dull battleship grey instead of the lined green livery they carried in MGWR days, they served the Achill line reliably to the last.