There were three locomotives used in the film: one as “The General”, one as “The Texas” and one for a spare. The spare engine had been originally intended to play The Texas, but the engine that ultimately got that role was found to be in better condition. The spare engine played the role of the Union engine up to the bridge scene, where it played The Texas as it crossed the bridge.
For the scene in which The Texas crashes through the bridge, Keaton spared no expense, using six cameras and thousands of local extras. It cost nearly $50,000 at the time and was the most expensive single shot of the entire silent movie era. The Texas itself remained in the river until WWII, when it was salvaged for scrap iron.
In the train crash a dummy was used as the engineer. The looks of shock on the faces of the Union officers were real, because the actors who played them were not told what was going to happen to that train.
The General (1926) dir. Buster Keaton & Clyde Bruckman