"Guys, wait! Look out for the barrier!"
The Diesel Headquarters is an old shed..
The Diesel Headquarters was seen as some sort of run down shed with broken machinery and pieces of scrap. One was a blue truck that was eventually modified into the Road-Rail Transporter. There is an oil derrick there as well, but is isn't seen being used. There is a small turntable in front of the sheds, to small for engines like D199 and Connor to use, implying it was made for the smaller troops of The Diesel Army. Although not the best fortress, it survived it's purpose all the way up until the point where Connor seized control of it.
Connor and his friends lead an attack on the fortress, but they were all defeated, accept for Connor, who battled Diesel. The diesels were kicked out and Connor seized control of it. The latter and Charlie had a machine constructed from the scrap and machines to make a lorry that would transport engines on road. Later, a letter arrived at the fortress, sent from 089, and gave instructions on how to find him.
- It is unknown what happened to the fortress after the ninth episode, Connor could have had it destroyed, or he could have just left it.