Rebuilding the pioneer of Cab Forward
SP got the MC-1 in 1909 - they were Malets with double expansion of the steam (Compound).
SP rebuilt them in the period from 1927-37 to simple - all four cylinders now have the same dimensions and use steam directly from the boiler, steam supply to the front pair of cylinders was realized by the large steam pipes on top of the boiler. With the rebuilding the boiler was also fitted with a new super heater - the dry steam used those pipes to reach the front pair of cylinders.