The World's Strongest Engine is the eleventh episode ever made in Season 6.
Henry needs to go to the works after being derailed, and unfortunately Diesel is the only engine available. The next day, the trucks tease Diesel at the Docks, so he boasts he can pull twenty of them at once. Diesel soon finds he is unable to move them (unbeknownst to him, a shunter has put the brakes on) and pulls so hard he breaks loose and falls onto a barge. Diesel is sent home in disgrace, while Henry, who is now repaired, pulls the trucks away.
- The term "trucks" is used in the American narration.