As locomotive designs developed, the difficult route of the Portpatrick an Wigtownshire line was unable to take advantage of large locomotive traction. Smith records that "At the end of March 1939 there came momentous news—official sanction for a 60 ft [18 m]; 4-6-0s to work to Stranraer". On 23 March 1939 a trial run was made with a 4-6-0, with the locomotive and tender separated at Stranraer to turn them. "There was no prospect of the 60 ft turntable being ready before late summer, so they laid longer rails, projecting at each end, on the existing 50 ft turntable. This allowed them to turn a Class 5 4-6-0. The class 5s began to work from Glasgow to Stranraer on 16 April 1939.