The class 15A was a 4-8-2 mixed traffic locomotive designed by D.A. Hendrie as a successor of the class 15. It was the last plate frame locomotive of this wheel arrangement designed by him and had the goal to address the overly long tubes of the class 15. The solution was to fit the Belpaire firebox with a combustion chamber that decreased the length of the tubes. This also enlarged the heating surface from 155 to 192 square feet.