▁West ▁Coast ▁until ▁the ▁ 1 9 4 0 s . ▁In ▁the ▁late ▁ 1 9 2 0 s ▁and ▁ 1 9 3 0 s ▁seven ▁locomot ives ▁were ▁fitted ▁with ▁narrow ▁fire box ▁super he ated ▁bo ilers ▁ ▁and ▁lever ▁type ▁reverse ▁controls ▁in ▁place ▁of ▁the ▁original ▁wheel ▁and ▁sc rew ▁type . ▁Other ▁alter ations ▁included ▁fitting ▁sand ▁dom es ▁and ▁a ▁new ▁type ▁of ▁fun nel . ▁The ▁remaining ▁three ▁locomot ives ▁were ▁with dra wn ▁by ▁ 1 9 3 7 . ▁ ▁The ▁super he ated ▁bo ilers ▁on ▁the ▁U C s ▁provided ▁better ▁performance ▁and ▁from ▁the ▁mid ▁ 1 9 3 0 s ▁they ▁saw ▁consider ably ▁greater ▁use ▁than ▁the ▁Bald win ▁built ▁U B ▁class ▁locomot ives . ▁They ▁were ▁still ▁being ▁used ▁on ▁passenger ▁services ▁as ▁well ▁as ▁coal ▁trains ▁in ▁the ▁mid ▁ 1 9 5 0 s , ▁however ▁the ▁arrival ▁of ▁more ▁A ▁Class ▁locomot ives ▁in ▁the ▁ 1 9 5 0 s ▁( dis pla ced ▁by ▁dies el isation ▁in ▁the ▁North ▁Island ) ▁allowed ▁their ▁withdraw al ▁by ▁ 1 9 5 9 . ▁Although ▁none ▁were ▁initially ▁preserved ▁a ▁number ▁were ▁dump ed ▁in ▁rivers ▁as ▁er os ion ▁prevent ion ▁measures , ▁and ▁two ▁have ▁been ▁recovered ▁for ▁potential ▁rest oration . ▁ ▁Pres ervation ▁In ▁March ▁ 2 0 0 5 , ▁the ▁newly ▁formed ▁Mid land ▁Rail ▁Heritage ▁Trust ▁in ▁conj unction ▁with ▁a ▁family ▁of ▁private