After the Klaww Gang's theft of the Clockwerk parts, Jean Bison used Clockwerk's Lungs and Stomach as a source of fuel for three of his trains. By outfitting each train's engine with one of the Clockwerk parts, they were able to run endlessly, which in turn increased the rate of spice shipments. Bison referred to these three trains as his "iron horses."
As the iron horse trains never stopped, the Cooper Gang was forced to board them while they were still moving. Bentley and Sly Cooper sneaked on-board iron horses no. 1 and 2, respectively, and made off with both of Clockwerk's lungs. Iron horse no. 3, however, was moving too quickly to board. So, the Gang used an old handcar to reach the back of the train, allowing Sly to jump on. He made his way through the interior and eventually reached the engine. Bison had wised up and bolted the stomach into place, so Bentley had to drop a bomb down the train's chimney to break it free.
With all three Clockwerk parts stolen, the iron horses were out of commission and spice shipment in North America was crippled.