This would be strictly conjecture, but I wonder if the diesel engine at the back of the short train was there to provide some braking power and some resistance so that the steam engine could be tested under load conditions not feasible with a few empties on level track. The German Federal railroad had engines specially modified as "Bremsloks" (braking locomotives) for testing new or modified locomotives under varying load conditions. Some members of otherwise extinct locomotive types such as the 45 class 2-10-2s survived years longer as braking engines. Just an idea.
Edited 1 time(s). Last edit at 02/08/2019 09:08PM by Olaf Rasmussen.