BCDR 4-6-4T

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.[2] 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 19 in × 26 in (483 mm × 660 mm) cylinders and 5 ft 9 in[lower-alpha 1] driving wheels compared to 22 in × 28 in (559 mm × 711 mm) cylinders and 6 ft 9 in driving wheels.[2] Despite this, at over 81 tons the locomotives were noted for being very heavy.[2]

Numbered 22 to 25, they were allocated to heavy commuter trains on the 12+1⁄4 miles (19.7 km) Belfast Queen's Quay to Bangor line.[5][lower-alpha 2] In service, the class was reliable but performance was mediocre and coal consumption was very high.[2] 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.[7]

The BCDR was absorbed into the Ulster Transport Authority (UTA) on 3 September 1948, and the class was renumbered 222 to 225.[8][3] Class WT 2-6-4T 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.[9] With the introduction of UTA MED diesel railcars, the Bangor line lost all steam working by 1953.[10] Only one worked past 1952,[3] with No. 222 surviving[lower-alpha 3] on the former Northern Counties Committee network with the remainder being withdrawn at Queen's Quay sidings.[9] All were ultimately scrapped in 1956.[9]