The Old Mine is a mine on the Skarloey Railway.
Prior to 1945, the mine had been closed down for many years. Following the closing of the Transfer Yards, Mr. Percival saw an opportunity in the old mine, considering reopening it to make up for lost profits.
Upon reopening the mine, he put Rusty and Duncan to work there. And after Percy lost his trucks on the viaduct and having them crash into the now shut down Transfer Yards, Mr. Percival purchases a new engine named Bertram after Sir Topham Hatt in retaliation.
During the events of Hatt, Bertram was entering the mine, when a workmen discovered a rock with Mr. M written on it,the miners clear and they along with Rusty and Duncan watch as the mine collapses trapping Bertram inside for the rest of 1945.