From the 1926 movie "The General"
The scene in which the locomotive crashes through the bridge was the single most expensive shot of the entire silent movie era. The locomotive itself remained in the river until WWII, when it was salvaged for scrap iron.
Based on a true incident during the Civil War. In April 1862, Union agent James J. Andrews led a squad of 21 soldiers on a daring secret raid. Dressed in civilian clothes, Andrews and his men traveled by rail into the Southern states. Their mission was to sabotage rail lines and disrupt the Confederate army's supply chain. At the town of Little Shanty, GA, the raiders stole a locomotive known as "The General." They headed north, tearing up track, burning covered bridges and cutting telegraph lines along the way. William Fuller and Jeff Cain, the conductor and engineer of "The General," pursued the stolen train by rail and foot. They first used a hand-cart (as Buster Keaton does in the film), then a small work locomotive called "The Yonah," which they borrowed from a railroad work crew, and finally a full-sized Confederate army locomotive called "The Texas," which pursued "The General" for 51 miles - in reverse. During the chase, Confederate soldiers were able to repair the sabotaged telegraph wires and send messages ahead of the raiders. Andrews and his men were intercepted and captured near Chattanooga, TN, by a squad of Confederate troops led by Gen. Nathan Bedford Forrest (who, after the war, was one of the founders of the Ku Klux Klan). Tried as spies, Andrews and seven of his raiders were hanged (a special gallows was built to hold all eight men). The rest of the raiders were traded in a prisoner exchange. In 1863 the survivors of the mission were awarded the first Medals of Honor (Andrews and the raiders who had been hanged later received the MoH posthumously).
Buster Keaton shot most of this film outdoors in Oregon because the narrow-gauge railroad tracks that could accommodate antique locomotives were still in use at the time.
When the Texas goes over the burning bridge and plummets into the river, 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.