During The Great Railway Show, these diesels were seen shunting trucks around the yard for the contestants; such as the heavy train for the Strength Competition. Three of them watched the Shunting Competition.
When James went to Bridlington to search for Thomas, he bumped into one of the diesels and asked him if he had seen the tank engine, who replied he could not remember. When James provided more details, the diesel asked another diesel, Ulli, if he had seen Thomas, who replied "Nope". The diesel then explained that Bridlington was a busy goods yard and left. After finding out from Thomas' trucks that he was at the Steelworks, James tried to ask the diesel if he knew where it was, only to be ignored.
The Mainland Diesels are based on the BR Class 08. Over seventy members of this class survive today in preservation, while around 100 remain in service on the national rail network. They were in fact the most successful shunting engines in the world, with 996 of them built. Diesel, 'Arry and Bert, Splatter and Dodge, Paxton, Sidney and the Diesel Shunter are also based off of this engine.
The diesel shunters are all painted in a livery similar to the EWS orange-red and yellow livery. They have black and yellow hazard stripes painted on their fronts, white ladders, yellow counterweights and red buffers.
- Ulli is the only known diesel shunter to be named.
- The diesel shunters all appear to have faces similar to Paxton, Sidney and Diesel (with minor modifications). One of the diesels also appears to have a face similar in appearance to Diesel's original face from the Thomas and the Stinky Cheese CGI test episode.