- 4 - 4 T ▁steam ▁locomot ive . ▁ ▁It ▁was ▁a ▁development ▁of ▁earlier ▁C aled onian ▁Railway ▁ 0 - 4 - 4 T ▁locomot ives , ▁including ▁the ▁ 1 9 ▁Class ▁and ▁ 9 2 ▁Class , ▁and ▁prede cess or ▁of ▁the ▁ 4 3 1 ▁Class . ▁ ▁The ▁ 4 3 9 ▁Class ▁was ▁introduced ▁by ▁John ▁F . ▁Mc Int osh ▁in ▁ 1 9 0 0 ▁and ▁a ▁modified ▁version ▁was ▁introduced ▁by ▁William ▁Pick ers g ill ▁in ▁ 1 9 1 5 . ▁ ▁Introduction ▁ ▁Nin ety - two ▁engines ▁of ▁the ▁class ▁were ▁built ▁between ▁ 1 9 0 0 ▁and ▁ 1 9 2 5 , ▁a ▁few ▁under ▁L MS ▁aus p ices . ▁ ▁Se vent y - four ▁Class ▁ 4 3 9 s ▁passed ▁into ▁British ▁Rail ways ▁ownership ▁in ▁ 1 9 4 8 ▁and ▁they ▁were ▁number ed ▁ 5 5 1 5 9 - 5 5 2 3 6 ▁( with ▁g aps ). ▁ ▁Ear lier ▁versions ▁▁▁ 1 9 ▁Class ▁Int rodu ced ▁ 1 8 9 5 ▁▁▁ 9 2 ▁Class ▁Int rodu ced ▁ 1 8 9 7 , ▁developed ▁from ▁ 2 9 ▁Class ▁ 0 - 6 - 0 T ▁ ▁The ▁ 1 9 ▁and ▁ 9 2 ▁Class es ▁were ▁originally ▁fitted ▁with ▁cond ens ing ▁appar atus ▁for ▁use ▁on ▁Glasgow ▁Central ▁Low ▁Level ▁lines . ▁ ▁Tw enty - four ▁of