BCDR 4-6-4T
The Belfast and County Down (BCDR) 4-6-4 T were a class of four 6-coupled tank locomotives build by Beyer, Peacock & Company in 1920. Generally reliable and well-liked but with mediocre performance, they spent their lives on the , Belfast to  until withdrawal in the early 1950s. These were the only class of  wheel arrangement to work in Ireland. History
At the end of World War I, the BCDR needed more powerful locomotives, and the directors were impressed by the LB&SCR L class express tank engines used on the London to Brighton line. Petterson thus ordered locomotive superintendent R. G. Miller to construct a class of similar engines. When the locomotives arrived in 1920 from Beyer, Peacock & Company they were inherited by Miller's successor Crossthwait. The BCDR locomotives were smaller than their English basis, with  cylinders and 5 ft 9 in driving wheels compared to  cylinders and 6 ft 9 in driving wheels. Despite this, at over 81 tons the locomotives were noted for being very heavy. Numbered 22 to 25, they were allocated to heavy commuter trains on the   to Bangor line. In service, the class was reliable but performance was mediocre and coal consumption was very high. Boocock has described them as "handsome" and "well-liked" and suggests the problem may have been due to short-travel piston valves rather than drafting. The BCDR was absorbed into the Ulster Transport Authority (UTA) on 3 September 1948, and the class was renumbered 222 to 225. Class WT  tank engines were transferred to the Bangor line from summer 1949 and their performance was substantially better, after which they began to replace the BCDR engines. With the introduction of UTA MED diesel railcars, the Bangor line lost all steam working by 1953. Only one worked past 1952, with No. 222 surviving on the former Northern Counties Committee network with the remainder being withdrawn at  sidings. All were ultimately scrapped in 1956. References

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Beyer, Peacock locomotives
Steam locomotives of Ireland
Steam locomotives of Northern Ireland
Railway locomotives introduced in 1920
4-6-4T locomotives
5 ft 3 in gauge locomotives