The Sodor & Mainland Railway owned two engines alongside Neil who, like him, had square tanks and open cabs. They operated on the railway until the line went bankrupt later on.
It is currently unknown what happened to the box tanks after the North Western Railway was formed, though they were most likely withdrawn from service and scrapped.
The Sodor & Mainland engines are based on the Neilson 0-4-0 box tank, which was a simple yet robust little tank engine with an unusual box-like shape and an open cab. Two of these engines used to work on the West Somerset Mineral Railway, but none survive to this day.
The Sodor & Mainland engines are believed to be painted green with red bufferbeams and gold sanding gear and safety valves. They had "S&M" as well as their numbers painted on the sides of their tanks in yellow and red lining.