Ministry of Defence Engine

According to The Island of Sodor: Its People, History and Railways, after the slate quarries on the Skarloey Railway closed, they were taken over by the Ministry of Defence for the storage of ammunition. The MOD used their own engine to shunt the sidings in the quarry, a black, electrically-powered engine described as being "beetle-like". This engine was never seen by any of the Skarloey Railway engines, due to the secret nature of its work.